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Tra Su - Tri Ton Reservoir for Flood Storage and Fresh Water Supply in An Giang Province

Feasibility Study Integrated Coastal Management Programme (ICMP)

Tra Su – Tri Ton Reservoir for Flood Storage and Fresh Water Supply in An Giang Province

Feasibility Study Integrated Coastal Management Programme (ICMP)

Authors:Dr. Thorsten Albers (von Lieberman GmbH, Germany)

Dr. Johannes Wölcke (UNIQUE, Germany)

Maximilian Roth (UNIQUE, Viet Nam)

Dr. Miriam Vorlaufer (UNIQUE, Germany)

Dr. Anke Reichhuber (UNIQUE, Germany)

Christina Pieper (UNIQUE, Germany)

Dr. Dang Thanh Lam (SIWRP, Vietnam)

July 2018

Table of Contents

List of tables .............................................................................................................iList of figures ......................................................................................................... iiList of sources of figures .................................................................................... iiiList of abbreviations ...........................................................................................iv

1 Executive Summary .......................................................................................01

2 Introduction ....................................................................................................02

3 Description of the Consultancy .................................................................033.1 FeasibilityStudyKick-Off ............................................................................... 33.2 Desk Study ....................................................................................................... 33.3 First Mission January 2018 ............................................................................. 43.4 Mission Report ................................................................................................ 43.5 Feasibility assessment ................................................................................. 10

4 Description of the Project Area .................................................................114.1 Topography .................................................................................................... 114.2 Hydrology ....................................................................................................... 114.3 Geology and soil ............................................................................................ 13

4.3.1 Geotechnical parameters .................................................................................................. 13

4.3.2 Soil chemistry ....................................................................................................................... 14

5 Description of the Proposed Project .......................................................15

6 Feasibility Assessment of the Proposed Project ..................................176.1 Technical Feasibility ..................................................................................... 17

6.1.1 General hydrology .............................................................................................................. 17

6.1.2 Location and dimensions .................................................................................................. 18

6.1.3 Assessment of evaporation .............................................................................................. 21

6.1.4 Assessmentofinfiltration ................................................................................................. 22

6.1.5 Water inlet ............................................................................................................................ 22

6.1.6 Water discharge................................................................................................................... 23

6.1.7 Hydrological model ............................................................................................................. 25

6.1.8 Summary of structural measures ................................................................................... 27

6.1.9 Geotechnical engineering ................................................................................................. 29

6.1.10 Slope protection .................................................................................................................. 35

6.1.11Considerationofchangingloads(e.g.traffic) ............................................................... 38

6.2 Institutional Feasibility ................................................................................ 386.2.1 Stakeholder Summary ....................................................................................................... 386.2.2 Laws and Regulations ........................................................................................................ 416.2.3 Options for institutional strengthening ......................................................................... 42

6.3 Environmental Feasibility ............................................................................ 436.3.1 Soil contaminants ................................................................................................................ 436.3.2 Soilacidificationandsoilmanagement ......................................................................... 446.3.3 Biodiversity ............................................................................................................................ 456.3.4 Tra Su Melaleuca forest ..................................................................................................... 47

6.4 Socio-economic Feasibility ........................................................................... 49

6.5 Economic Feasibility ..................................................................................... 55

6.6 Environmental and social safeguards ........................................................ 57

6.7 Capacity development needs ...................................................................... 626.7.1 Capacity development options ........................................................................................ 64

7 Key Findings and Recommendations ......................................................65

8 Conclusions ......................................................................................................67

9 Reference list ...................................................................................................68

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LIST OF TABLES

Table 1: Soil parameters in the project area .............................................................................................. 13

Table 2: Characteristics of two climate change scenarios ....................................................................... 18

Table3:Volumesofdifferentdesignalternatives ..................................................................................... 20

Table4:Maximumflowthroughthesluicegatesincaseoffloodrelease ......................................... 24

Table 5: Key facts of the proposed reservoir .............................................................................................. 27

Table 6: Values of the assumed layering of the subsoil, .......................................................................... 29

Table7:Partialfactorsonactionsortheeffectofactions ...................................................................... 30

Table 8: Partial resistance factors for spread foundations ..................................................................... 30

Table 9: Partial factors for soil parameters ................................................................................................. 30

Table 10: Geotechnical calculation regarding setting and base failure ............................................... 33

Table11:Resultsofthecalculationtofindthelimitedstate .................................................................. 34

Table 12: Stakeholder Summary .................................................................................................................... 39

Table 13: Overview on laws and regulations .............................................................................................. 41

Table 14: Overview on Ecosystem services of wetlands .......................................................................... 47

Table 15: Scale of reservoir (Option 4) ......................................................................................................... 49

Table 16: Construction costs .......................................................................................................................... 49

Table 17: Seasonal calendar of double rice cropping system ................................................................ 50

Table 18: Agricultural budget for double rice cropping system ............................................................ 50

Table 19: Scaling overview alternative livelihoods (six-year scenario) .................................................. 54

Table20:Overviewofperhacashflowsforlivelihoodalternatives ..................................................... 54

Table21:Totalcashflowsoflivelihoodalternatives ................................................................................. 54

Table 22: Summary of results from economic analysis ........................................................................... 56

Table 23: Environmental and Social Safeguards assessment (based on World Bank Environmental Social Standards) ................................................................................................. 59

Table 24: Capacity SWOT analysis on central/regional as well as provincial level ............................. 62

Table 25: Overview of direct capacity development options .................................................................. 64

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LIST OF FIGURES

Figure 1: Project area and proposed reservoir .............................................................................................2Figure 2: Inlet area (left) and rubber dam (right) ..........................................................................................7Figure 3: Eastern (left) and western embankment (right) ...........................................................................8Figure 4: Main canal in Hon Dat district in Kien Giang Province ...............................................................9Figure 5: General map of the Mekong River in Vietnam .......................................................................... 11Figure6:WaterlevelinthefloodseasonatXuanTostation ................................................................. 12Figure7:FloodflowdirectionintheMekongDeltaduringfloodintheyear2000 .......................... 13Figure 8: Projected reservoir with sluice gates 1-6 ................................................................................... 16Figure 9: Overlay of the reservoir area with aerial photo ........................................................................ 16Figure10:Simplifiedhydrologicalscheme .................................................................................................. 17Figure 11: Area of the reservoir without the Tra Su forest ..................................................................... 19Figure 12: Scheme of the reservoir ............................................................................................................... 19Figure 13: Alternative reservoir area with additional area south of the excluded Tra Su forest ... 20Figure 14: Alternative reservoir area with additional area south of the excluded Tra Su forest ... 21Figure 15: Required pumping rates to balance evaporation .................................................................. 21Figure16:Infiltrationratesandrequiredpumpingtobalanceinfiltration ......................................... 22Figure17:Inletflowthroughonesluicegatewiththewidthof40mdependingon

the water level in the Vinh Te canal .......................................................................................... 23Figure 18: Discharge through the projected sluice gates ....................................................................... 24Figure 19: Absorption pool with hydraulic jump........................................................................................ 25Figure20:Waterlevelsandfreshwaterusagefordifferentalternatives ........................................... 26Figure 21: Typical cross section of the west embankment ..................................................................... 31Figure 22: Stress curve below the embankment. ...................................................................................... 32Figure 23: View of the circular slip, when the limit state is exceeded. ................................................. 34Figure 24: Maximum slope of 19.9°, with view of a possible slope slip. .............................................. 35Figure 25: Full grouting (left) and partial grouting (right) ......................................................................... 36Figure 26: placed riprap (top); dumped riprap (middle); gabions (bottom) ........................................ 36Figure 27: Plank wall ......................................................................................................................................... 37Figure28:Fascines(left)andfascinesfilledwithstones(right) ............................................................. 37Figure 29: Assumed dimensions of various vehicles ................................................................................ 38Figure30:Seasonalchangesinecologyoverthefloodcycle ................................................................. 46Figure 31: Floating gardens in Bangladesh (Source: Rahman) ............................................................... 51Figure32:Lotusfishfarm ................................................................................................................................ 53Figure 33: Sensitivity of IRR dependent on scaling of reservoir area assigned to agricultural production................................................................................................................. 56Figure 34: Sensitivity of IRR dependent on frequency of drought event ............................................. 57

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LIST OF SOURCES OF FIGURES

Figure 1: Thuy Loi University Consultant Company Limited (TLUC)Figure 2: Thorsten AlbersFigure 3: Thorsten AlbersFigure 4: Thorsten AlbersFigure 5: Thorsten AlbersFigure 6: Thuy Loi University Consultant Company Limited (TLUC)Figure 7: SIWRRFigure 8: Thuy Loi University Consultant Company Limited (TLUC)Figure 9: Google EarthFigure 10: Thorsten AlbersFigure 11: Google EarthFigure 12: Thorsten AlbersFigure 13: Google EarthFigure 14: Thorsten AlbersFigure 15: Thorsten AlbersFigure 16: Thorsten AlbersFigure 17: Thorsten AlbersFigure 18: Thorsten AlbersFigure 19: http://docplayer.org/docs-images/51/28145902/images/15-0.pngFigure 20: Thorsten AlbersFigure 21: Thuy Loi University Consultant Company Limited (TLUC)Figure 22: Thorsten AlbersFigure 23: Thorsten AlbersFigure 24: Thorsten AlbersFigure 25: Bundesanstalt für Wasserbau (BAW)Figure 26: Bundesanstalt für Wasserbau (BAW)Figure 27: Technisches HilfswerkFigure 28: Technisches HilfswerkFigure 29: Schneider BautabellenFigure 30: Coates Figure 31: RahmanFigure 32: IUCNFigure 33. UNIQUEFigure 34. UNIQUE

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LIST OF ABBREVIATIONS

CBA Cost-benefit-analysisDARD Provincial Department of Agriculture and Rural DevelopmentDoNREDWR

Department of Natural Resources and EnvironmentDirectorate of Water Resources

FS Feasibility StudyGIZ Deutsche Gesellschaft für Internationale ZusammenarbeitHCMC Ho Chi Minh CityICMP GIZ Integrated Coastal Management ProgrammeIUCN International Union for the Conservation of NatureLXQ LongXuyenQuadrangleMARD Ministry of Agriculture and Rural DevelopmentMD Mekong DeltaPoR Plain of ReedsPPC Provincial People’s Committee SEA Strategic Environmental AssessmentSIWRP Southern Institute for Water Resources PlanningSP Sub-projectToR Terms of ReferenceTLUCVNDMA

Thuy Loi University Consultant Company LimitedVietnam Disaster Management Authority

WB World Bank

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The dynamism of the Mekong Delta

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The GIZ feasibility study Tra Su – Tri Ton Reservoir for Flood Storage and Fresh Water Supply in An Giang Province provides a comprehensive technical evaluation of fresh water retention in the Mekong Delta in Vietnam.

The general idea of the reservoir was raised by An Giang Province. A national consultant prepared a draft design for the envisaged investment. It was proposed to take fresh water from the Vinh Te Canal at the end of the rainy season while water levels in the canal are still sufficient, store thewater and release it for the purpose of fresh water supply of surrounding areas in the dry season. On theonehand,thisallowsforsufficient freshwatersupply during pronounced drought periods, and on the other hand it reduces pumping costs in the surrounding areas. The proposed design uses existing structures such as embankments and canals complemented by additional sluice gates, pumping stations and embankments to be constructed as part of the project.

This feasibility assessment is supposed to assess the overall feasibility of the proposed reservoir mentioned above, present the key findings of theassessment and give recommendations concerning the implementation and further steps.

The initial phase of this consultancy consisted of the first consultation and field survey for datacollection in January 2018 followed by the actual feasibility assessment in February and March 2018. The assessment is based on information and data collected as part of an initial analysis conducted by a Vietnamese consulting firm.Additional information and data were collected during the first consultation. The various analysesand proofs, including the analysis of the socio-economic impacts, were conducted based on that combined data set. After this draft report has been submitted,asecondconsultationincludingthefinalworkshop will take place in April 2018. Results of the study will be presented to the GIZ Team and other stakeholders. Comments and recommendations will be incorporated in the presentation, and afterwards consideredinthefinalreport.

As part of this consultancy, the overall water balance, considering hydraulic and hydrological aspects, were analysed. Relevant hydrological processes such as evaporation, precipitation and infiltration were considered and implemented ina simplifiedmodel.Water input from the Vinh TeCanal was identified as a key issue. The generaloperation of the reservoir was assessed, whereas environmental impacts were considered as decisive. The proposed overall design was adapted based on the initial results and the most promising alternative

was studied in depth. The hydraulic efficiencyof the proposed structures was also assessed. Geotechnical proofs of settlement, base failure and slope failure of the projected embankments were computed. The maximum height of an embankment and the limiting slope were analysed. The results were used to derive recommendations regarding the implementation of the earth works.

Generally, the overall water balance allows the operation of the reservoir as proposed from a hydraulic and hydrological perspective. A key aspect for thecostsandbenefitsof theproposedreservoir are its dimensions. Although the draft design canbe consideredas cost-efficient since ituses existing structures, extensive earth works and further structures are required to complete the reservoir. We recommend to avoid dredging since the costs for earth works and required follow-up costs will significantly increase the project costs.Further, dredging will complicate the approval procedure due to serious environmental impacts. We also recommend to exclude the Tra Su forest from the project area. A long-lasting inundation will seriously harm the forest and ecosystem. Thus, the adapted dimension of the area due to an exclusion of the Tra Su forest and the reduced water depths due to avoided dredging, reduces the area and the maximum storage volume and as a consequence also the benefits of the project. Evaporation isconsidered to induce significant pumping effortsfor the maintenance of the water level. The computed settlement should be balanced by a super-elevation of the respective embankments. The risk of base failure limits the maximum height of the embankments. Thus, the water volume of the reservoir cannot be increased by heightening the embankments.

Compensation mechanisms for the loss of land or livelihood incomes of local communities were also identifiedasakeyissue.Theinstitutionalfeasibilityaddressed inter-provincial, cross-border and national level coordination to ensure mitigation of potentialnegativeeffectsandinclusioninintegratednational, regional and provincial planning processes. In this context, capacity development needs were identified.

The results of the economic analysis reveal that the economic profitability of planned reservoir isquestionable at this point. Only under optimistic scaling assumptions, the project would be profitable.Therefore,theeconomicsoftheprojectshould be carefully considered as part of the further preparation process. The results indicate already that the selection of the alternative livelihood models andtheimplementationwillbekeyifprofitabilityofthe interventions is an important objective.

1. EXECUTIVE SUMMARY

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Rice production in An Giang Province has an annual output of more than 3.6 million tons, including an amount of 500,000 to 600,000 tons for export. In recent years, An Giang Province has applied innovative production technologies and introduced high value rice varieties to meet the requirements of large-scale rice production. Further, this step was supposed to increase the competitiveness in the process of international economic integration. Thus, An Giang Province’s vision for the agriculture sector is a development pathway of modernization.

However, impacts of climate change and sea level rise, prolonged droughts and lack of water resources due to the construction of reservoirs upstream the Mekong River have caused serious damage to agricultural production of the province in particular and the Mekong Delta in general. For example, despiteasufficientforecastofthedroughtinwinter-spring 2015-2016 and the timely support from the government, the damage on rice production in the MekongDeltawasstillsignificant.

Consequently, a combination of non-structural measures, such as changing cropping systems and patterns or transforming production models, and structural measures, such as reservoirs, in order

to increase the capacity of fresh water storage, was proposed. In this context, the Tra Su – Tri Ton reservoir project to store flood and supply freshwater was designed. The envisaged reservoir is located in Tinh Bien District that is at the downstream side of Tha La rubber dam and Tra Su rubber dam (see Figure 1 below). The main objectives of the proposed investment are:

Flood control from Cambodia into the Gulf of Thailandandfloodcontrolofthesouthernnationalroad 91 to protect the area of the Summer-Autumn crop and increase the area of Autumn-Winter crop in the project area. Here, the Chau Doc-Tinh Bien flood drainage network, within the Long XuyenQuadranglefloodcontrolsystem,isintendedtobepro-actively operated.

y Flood storage and supply of fresh water for agricultural production.

y Promote aquaculture in the Winter-Spring and Summer-Autumn crop seasons.

y Proactively respond to climate change, in particular prolonged drought and saltwater intrusion.

2. INTRODUCTION

Figure 1: Project area and proposed reservoir

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 4

Figure 1: Project area and proposed reservoir

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3.1 Feasibility Study Kick-Off

The assignment was initiated in December 2017. An internalkick-offcallwasconductedtomobilizetheconsultantteam,finetunetheworkplanandfurtherspecify the roles and responsibilities of each expert.

Of the core tasks of this assignment especially task 1-3 (desk study, including stocktaking of existing dataandinformationandidentificationofadditionaldata/information) were discussed in the initial phase. Generally, all tasks were carried out in a logical sequence as they build on each other. The desk study consists of a thorough review of the proposal documents in order to get a deep understanding of the proposed project. Due to related previous assignments, a general understanding of the project already existed, and the schedule could be slightly adapted so that the first consultancy and fieldsurvey for data collection were planned for late January 2018.

The following documents have been available and reviewed so far:

y Executive Summary of Project Proposal Tra Su – TriTonReservoirtostorefloodandwatersupplyfresh water by South Branch Thuy Loi University Consultant Company

y Respective project presentation by South Branch Thuy Loi University Consultant Company

y Collection and assessment of background information for a Water Retention Strategy for the LXQandPoRintheVietnameseMekongDeltabyKoos Neefjes and Le Anh Tuan, November 2017

y GIZ ICMP Feasibility Study Water Management in the Upper Mekong Delta conducted by UNIQUE in 2016

y Operational regulations for Long XuyenQuadrangle irrigation system, issued by MARD on 20 December 2017

3.2 Desk Study

Thefirstevaluationoftheavailabledocumentsledto several technical questions that needed to be clarified during the first consultation. Additionally,requireddataanddocumentshavebeenidentified.Generally, the main topics of the initial evaluation of the available technical documents provided by theVietnameseconsultingfirmcanbedividedintothreedifferentmodules:

y Hydrology

y Hydraulics

y Soil management

In the Executive Summary and the presentation of the project there are some inconsistencies with respect to the calculation of the project area, the storage volume and respective water levels within the reservoir. These calculations, including the basis ofterrainelevation,neededtobeverified.Relevantshape files of the reservoir, including the digitalterrain model, are required to verify the calculations.

Further, the Executive Summary mentions technical reports about the operational regulations of the LXQ irrigation system. These information on theregulations and additional information such as plans and planning with regards to land-use, water and irrigation, flood management, agriculture,aquaculture, forest, transportation – of the Mekong Delta,theLXQ,andconcernedprovinces,especiallyAn Giang and Kien Giang were considered according to their availability.

The desk study also revealed that existing models for developing the operational regulations for the LXQirrigationsystem(partiallyfundedbyGIZ)needto be discussed and evaluated.

The water discharge from the Vinh Te canal into the reservoir is a key issue of the project. Pumps are proposed to be installed. This raises the question whether it is not feasible to use the dams for a

3. DESCRIPTION OF THE CONSULTANCY

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controlled input. In this context, it was proposed that the hydrological regime and the proposed model for managing the reservoir need to be evaluated andverified.

Further, a more detailed list of construction costs is required to evaluate the cost estimate. In this context, geo-engineering aspects such as the foundation of dams, dykes and sluice gates have beenidentifiedasonekeyissue.Additionaldetailedinformation from the conducted geological survey are crucial as they allow a more precise calculation of construction costs. For a sound technical design and a detailed cost estimate, additional information on the subsoil are also important.

Overall, the desk study came to the conclusion that the above mentioned technical questions about the hydrology, hydraulics and soil management need to beansweredbefore thecostsandbenefitsof theproject can be assessed.

3.3 First Mission July 2018

The initial phase of this consultancy consisted of the firstconsultationandfieldsurveyfordatacollection.Thisfirstconsultationincluded–amongothers–theassessment of the project location and basic design and thorough consultation with relevant authorities, agencies and stakeholders at central, regional and provinciallevel.Keyobjectiveofthefirstconsultationwas the validation of the research questions and the detailed work-plan of the feasibility study involving all relevant key stakeholders by the conducting of a small workshop. The mission plan had been discussed and developed in close cooperation with GIZ ICMP. The participants, the program and the main objectives were listed in the Inception Report.

3.4 Mission Report

On January 19th, a meeting was held at MARD Directorate of Water Resources (DWR) in Hanoi with amongst others Mr. Do Van Thanh (Deputy General Director) and Mr. Hoang Anh Tuan (Deputy Director). At first, the consultants described thegeneral concept of the reservoir, since the proposal was not known.

In the following discussion, the international relevance of the rubber dams and the Vinh Te canal

was mentioned. Thus, the proposed project must be in line with international regulations and e.g. the Mekong River Commission should be informed. So far, the reservoir is not part of any approved planning and the proposal was initiated by An Giang province with the main objective to ensure sustainable socio-economic development. An integrative participation of MARD in the planning process is essential.

The realization of the reservoir will change the entire water management system in that region. A revision of the existing operational plans for water management for An Giang and Kien Giang would be required. To assure an early inter-provincial approach, it was recommended to invite the former chairman of PPC An Giang to the workshop of the firstconsultation.

It was mentioned that the water supply in the region of An Giang, where the reservoir is planned, isstillsufficient.Theissueoflackofwaterisalargerthreat for Kien Giang than it is for An Giang. Thus, a detailedcost-benefit-analysis(CBA)isconsideredascrucial.Intheeconomicefficiencyanalysisitmustbeconsidered that not every year a drought threatens the area.

A hydraulic design, in which the Vinh Te canal is the only water input for the reservoir, is considered as risky since the water level in the Vinh Te canal can be very low in some years. The LXQ is veryimportant for flooddrainage.Anadaptedpositionof the inlet further downstream in the Vinh Te canal is considered to bemore effective for floodcontrol. In this context it was mentioned that there are approved plans to replace the rubber dams by concrete sluice gates. At the moment the rubber damsareusedtoflushthericefieldsintheprojectarea. If the reservoir is constructed this function would be limited. In addition, due to the 2 rubber dams having transboundary implications, thoughtful consideration of the position of intakes is necessary.

The size of the reservoir and the assumed water demand is considered to be too large. It was suggested to design 3 or 4 separate compartments within the reservoir that can be managed separately and that would allow a better control, especially in case of incidents.

It was pointed out that the subsoil in the entire project area consists of soft soils. The foundation of constructions including dykes and embankments is complex. Slope failure must be considered in the geotechnical design taking into account dredging

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and the construction of the embankments. Furthermore, in the entire area acid-sulphate soils exist. This must be considered in the projection of the soil management. Generally, the proposed dredging of soil is seen very critical. As a consequence, the actual capacity of the reservoir might be quite smaller than the one currently designed. Overall costs for maintenance dredging in the canals in the Mekong Delta are very high. Those costs will also apply within the reservoir. This must be considered since sedimentation is assumed to be large.

The impacts of the construction of elements such as sluice gates on fish paths must be checked.The development of the water quality must be considered since pollutants will be mobilized.

The linkage between the reservoir and the Tra Su melaleuca forest must be considered.

Generally the term reservoir is considered as not exact enough, since flow through the reservoiris possible and planned. It was recommended to suggestdifferenttermsfortheplannedproject.

Also on January 19th a meeting was held at MARD Vietnam Disaster Management Authority (VNDMA) in Hanoi with amongst others Mrs. Doan Thi Tuyet Nga (Director) and Mr. Ta Ngoc Tan. Generally, An Giang has been identified aspotential area for the storage of fresh water. There is a consensus of the provinces An Giang and Kien Giang that water storage needs exist. However, the project area is not the area with the largest water shortage and no severe damage has occurred there so far. The interest of An Giang Province to store water considers future scenarios.

It was assumed that the required cooperation between An Giang and Kien Giang will work very well. ItwasalsoconsideredthatKienGiangbenefitsfromthe reservoir. The An Giang-Kien Giang floodway,that was part of the World Bank 9 Project (WB-9), had been discussed very controversial. The actual status of that project was not clear.

It was discussed that the proposed concept is differentfromtraditionalwaterstorageinreservoirs.The concept and idea needs to be explained in depth including detailed hydraulic planning. It was mentioned that generally a reservoir keeps water inside set boundaries without significant flowthrough the reservoir and that the planned reservoir isdifferentsinceitallowssignificantflowrates.Thus,adifferentdesignationwasrecommended.

The proposal must match legislations for the construction of embankments, dykes and sluice gates. For every larger reservoir operational regulations are crucial. VDMA is interested in discussing questions of e.g. of dyke heights within this project, since water management is closely related to risk reduction.

On January 22nd an internal meeting was held at Southern Institute for Water Resources Planning (SIWRP) in HCMC with the national and international consultants and Mr. Vu from GIZ ICMP. The national consultants were informed about the meetings at MARD. It was pointed out that the status of World Bank Subproject 9 is not known and mustbeclarifiedsinceitwasplannedforthesamearea and partly contradicts the proposed reservoir. The purpose of the proposed reservoir is limited to aspects of water storage and water supply. It does not fulfil tasks of flood protection. The availableexecutive summary is based on a simplifiedhydraulic assessment. Socio-economic aspects have not been assessed in depth either. The main reasons for the construction of the reservoir are economic reasons. Thus, the economic analysis is very important. During the extreme drought in 2016 the lowest measured discharge (within an 80 year time series) in the Hau River occurred. This extreme event was assumed to have a recurrence interval of approximately 100 years. This must be considered inthecost-benefitanalysis.

On January 22nd a meeting was held at Thuy Loi University Consultant Company Limited (TLUC) in HCMC with amongst others Mr. Pham Cao Tuyen (Director). This is the technical institution which helped An Giang PPC/DARD designing the reservoir.Atfirst,apresentationoftheproposalwasgiven. It was identical with the presentation that was provided by GIZ before the consultation apart from two slides about water levels in the Vinh Te canal.

After the presentation, several open questions were discussed. A constant flow through the reservoirwas assumed in the basic hydraulic design. It will be realized by pumping for approximately 50 days per season. The according volume explains some of the inconsistencies in the calculated maximum storage volume of the reservoir. The very early planning status of the project became clear. Thus, some of the open points remained unexplained.

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On January 23rd a meeting was held at DARD An Giang inLongXuyenwithamongstothers theDirector of DARD, the Director of the Irrigation Department, representatives of the relevant DistrictsandarepresentativeofTLUC.Atfirst, thepresentation of the previous day was given by TLUC. TLUC developed the presented basic proposal based on a cooperation with An Giang Province without anyfunding. Itmustbeconsideredasafirstdraft.Many aspects such as the title, exact geographical coverage (Tinh Bien district, not Tri Ton as currently formulated), exact boundary and volumes, depth/elevationandmanagementofthesoilanddifferentlivelihoodmodels–needtoberefinedandfurtherconsidered.

After the presentation, the Director of DARD highlighted the importance of issues of water management and water supply for An Giang province. During a workshop in September 2017 with representatives of the Dutch embassy, GIZ and An Giang and Kien Giang provinces these topics were identified as challenges of higher priority. Itwas agreed that two general pilot models for the Mekong Delta should be investigated: (i) larger scale reservoirs covering areas of 2,000 to 10,000 ha, and (ii) smaller scale reservoirs. The investigation of the feasibility of smaller reservoirs will be done by IUCN. The projection of the larger scale reservoirs was handed over to DARD An Giang. A decision for one model based on feasibility studies and under integration of MARD was expected for 2019.

The reservoir must be integrated in the provincial developmentplansinceitinfluencesthelanduseinthat area. It also widens the scope of the province during extreme events. During the drought in 2016, Vietnam had to ask China to open upstream dams so that water levels in the Hau River increase. It was assumed that also Kien Giang benefits from thereservoir in case of extreme events. GIZ ICMP has moderated a cooperation of An Giang province and Kien Giang province. The proposal of the reservoir needs to be considered in the discussion between the two provinces. Benefits for Kien Giang mustbecome clear.

In the discussion, a project of the World Bank on water management between Vietnam and Cambodia was mentioned. The interaction between this project and the proposed reservoir needs to be considered.

The crest of the rubber dam has an elevation of 3.8manddoesnothaveasufficientheightfortheprojected reservoir. In the FS it should be considered that both rubber dams will be replaced by the sluice gates mentioned in the executive summary. Those sluice gates are approved and the construction is supposed to start in 2018. At the moment the tender process is running. The construction costs for the sluice gates should not be included in the FS since they are from other funds.

The status of World Bank Project (WB-9) is still uncertain andmust be clarified since it interfereswith the planning of the reservoir. The unofficialopinion was that it was cancelled due to the cost-benefit-ration. Thus, a sound cost-benefit-analysismust be an essential part of the FS for the proposed reservoir. The main purpose of the reservoir is the storage and supply of fresh water. But, it should be checkedifitcanbeoperatedtostorepeaksoffloodwater levels.

Generally,threekeyissueshavebeenidentifiedbyDARD An Giang that need to be addressed in the FS:

y Technical planning

y Livelihood models

y Effectsonoverallwatermanagement

In the discussion it was considered as possible that alackofwaterintheVinhTeCanallimitsthefillingof the reservoir. Thus, the general hydrology and the operational regulations for the sluice gates are crucial and should be optimized based on existing models. Additional water input through the sluice gate in the eastern part of the reservoir should be checked.

The FS should deal with geo-engineering aspects, such as the settling due to the heightening of the embankments and slope failure of the embankments under high water levels within the reservoir and with soil management, such as the handling of the dredged soil. Due to the long duration of inundation of 7 months, the slope stability needs to be checked in detail. Generally the embankments should be as high as possible to create a maximum volume within the reservoir, but also the risks of storing such a large amount of water was mentioned. It was mentioned that the geology changes over the project area. Especially in the western part more information about the subsoil is required. The load bearing capacity of the roads on the embankments should be considered. In this context it was assumed that

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higher loads on the embankments will occur due to increasingtraffic.

The dredging of soil was seen very critically since it will decrease the quality of the soil for agricultural purposes and thus influence the livelihood.Compensation for this decrease in quality are not planned. Dredging requires the permission of the Prime Minister. The position of DARD is to avoid dredging and increase the heights of the embankments as far as possible. In the FS the structural limit of dyke height should be assessed.

Another key issue is the interaction of the reservoir with the Tra Su melaleuca forest. The water management of the forest lies in the responsibility of DARD. Thus, a coordination is feasible. If the reservoir is constructed, a detailed operational management plan for the Tra Su forest must be created by which the operations of the sluice gates should support or facilitate the water management in the forest. Erosion in the forest due to high current velocities in case of opened sluice gates must be avoided. Last but not least important, how to control and manage the quality of water from the forest once it is part of the reservoir – is still an open question.

DARD suggested different livelihood models thatcould be applied if the reservoir is constructed. These models need to be addresses in the FS.

y During the flood season (while the reservoiris inundated) local farmers are employed by a private company that cultivates the area. Land-use could be Lotus farming including eco-tourism or aquaculture.

y During the dry season the local farmers work as before.

y Handover of the operation of the reservoir to a (government owned) company that manages the irrigation. Local farmers get compensated from that company.

The operations and maintenance of the reservoir could be handed over to a government owned company, to a private company or can be a combination of both. According monitoring equipment needs to be considered in the cost calculation.

In the proposal aquaculture and lotus farming was recommended as an alternative livelihood during inundation of the reservoir. It needs to be checked if thewaterqualityissufficient.Watertransportationshould be addressed in the FS. It was not clear if it is significantintheprojectarea.

Figure 2: Inlet area (left) and rubber dam (right)

8

On January 24th on a field trip to the projected area of the reservoir in Tinh Bien District the inlet areaincludingtherubberdamwerevisited(figure2).

TheproposaloftheAnGiang-KienGiangfloodwaypartly contradicts the planning of the reservoir. Thus, the status of sub-project 9 of the World Bank needs tobeclarified.IntheFSitneedstobecheckedifthesoil quality in the reservoir area is suitable for other livelihood models. It was assumed that additional data is required for that. If one crop rice per year is lost,thebenefitsofthereservoirarequestionable.Thus, a CBA is very important. Alternative livelihood models for the local people are crucial for the evaluation of the proposal. Compensations for local farmers play an important role.

In the assessment of the technical feasibility, the loss of water through infiltration and evaporationmust not be neglected. Technical details, such as thedykedesign,mustbeclearastheysignificantlyinfluence the costs and benefits of the reservoir.The amount of pumped water needs to be assessed morepreciselysinceithasaninfluenceontheCBA.

The exact location and dimensions of the planned reservoirneedtobeverifiedsincetheysignificantlyinfluencetheaffectedareaandnumberofpeople.Itshouldbeclarifiedwhobenefitsfromthereservoir.The combination of suitable livelihood models is essential for the success of the project.

Besides the CBA a Strategic Environmental Assessment (SEA) is essential since the reservoir will have an impact on the biodiversity of the Tra Su forest.

Figure 3: Eastern (left) and western embankment (right)

Afterwards the existing embankments at the eastern and the western boundary of the projected reservoir wereinspected(figure3).

At the southernmost location of the reservoir it was recognized that the northern part of the Tra Su forest is included in the proposed reservoir area. This is not consistent with the description of the project and the executive summary and must be clarified. Generally, the eastern embankmentshave a sufficient height and paved slopes. Thesteep slopes must be checked against geotechnical stability.Onemajorcanalflowsintotheprojectareafrom eastern directions. Here, the design of the projected sluice gate must be checked carefully. The embankments on the western sides do not have a sufficientheightandstability.Thesubsoilconsistsofsoft clay. Settling is visible at many locations along the road.

On January 25th a meeting was held at DARD Kien Giang in Rach Gia with amongst others the Vice Director of DARD, Director of Irrigation Sub-department, Chief of water management section from DONRE and Vice director of Kien Giang weather station. It was mentioned that it must be checked if the proposed reservoir is in line with existing operational regulations. Available upstream volumes in the Vinh Te canal must be checked and be integrated in a consistent management plan for the reservoir. In this context impacts on downstream areas must be clear and negative impacts must be avoided.

9

DARD Kien Giang sees the possibility that the reservoir might induce benefits for Kien Giangprovince. Thus, a general interest to support the proposal exists. Conflicts of interest between thetwo provinces must be addressed in the FS. Possible effects of the reservoir on saline intrusion in KienGiang need to be considered.

On a field trip to Hon Dat District in Kien Giang province on January 25th some of the main canals which are connected to the proposed reservoir area have been visited (figure 4). The distance tothe reservoir was approximately 37 km, and it was agreed that the impacts of the reservoir on this part of the province are limited.

expressed general agreement with the proposal, but addressed the need for further investigations.

The Vice Director of DoNRE also expressed general agreement and considers the subject of water supply as crucial. But it must be quantified whobenefitsfromthereservoirandtowhatextent.AnGiangdoes not suffer froma lack ofwater at themoment.

The Vice Chairman of DARD Kien Giang shared the opinion that an inclusion of the Tra Su forest in the reservoir cannot be recommended. He expressed general agreement but reminds to check the general dimensions. Kien Giang province will construct sluice gates along the coastline so that saline intrusion will be minimized. Thus, the main purpose of the reservoir is water supply for the irrigation and the effectofthereservoironminimizedsalineintrusionwillnotbesignificant.Incaseofwaterreleasefromthe reservoir, lower dykes constructed by local people might be endangered. These local effectsshould be addressed in the FS. The compensation of the farmers in the reservoir are a key issue. Funds for the maintenance of the embankment within and surrounding the reservoir must be considered in the CBA because after 7 months of inundation there will bedamagesattheinfielddykesandinfrastructures.

The Forest Department expressed the opinion to exclude the Tra Su forest from the reservoir area. The changing water regime will have negative impacts on the forest. On the other hand the forest couldbenefit fromadditionalwater supply. In thiscontext it is important to discuss the question who will operate the reservoir.

Inyearswithlowerwaterlevelsof1-2minthefloodseason pumping to fill the reservoir is significant.These events must be considered in the CBA of the FS. The operational regulations of the reservoir mustbeclarified includingstoragevolumes,waterdemand and usage etc. It was agreed that the proposed location of the reservoir is generally feasible because construction costs could be minimized due the existing embankments. But, in the FS different areas for the reservoir can beconsidered.

The acceptance of the local people is considered as crucial. A comprehensive study of socio-economic aspectsanddifferentlivelihoodmodelsisessential.

Figure 4: Main canal in Hon Dat district in Kien Giang Province

On January 26th a summarizing workshop was held at the Guest House of PPC An Giang in Long Xuyen.Afterajointpresentationofthenationalandinternational consultants describing the outlines of the project and the main findings of the firstconsultation, the presentation and the proposal in general were discussed.

It was stated that the construction of the sluice gates at the Vinh Te canal will start in 2018 and will replace the rubber dams. The energy consumption for the pumping of 50·106 m³ water needs to be considered.

A clear statement of the former PPC chairman was not to include the Tra Su melaleuca forest in the reservoir area, since the ecosystem will change. He

10

Changed livelihoods must be considered in the FS. Eco-tourismisconsideredasapossibleco-benefit,but the extent of the benefit was considered aslimited. The associated costs and benefits willeither be studied in this FS whenever possible, or recommended for further detailed studies during the project formulation stage. This will give evidences for local authorities in negotiating and convincing involved farmers.

Gender aspects and ethnic minorities should be considered in the FS. If the reservoir is inundated for 6 or 7 months with water levels up to 5 m, the danger of drowning of children must be dealt with.

A de-briefing of the national and internationalconsultants with GIZ ICMP completed the mission. Next steps and the general schedule were discussed and decided.

Two intended meetings with CPO10 in Can Tho and with Dr. Andrew Wyatt from IUCN will be realized by the national consultants, and via Skype by the international consultants respectively. This should be done before further in-depth assessments are being conducted.

3.5 Feasibility assessment

The next step after the first consultation wasthe actual feasibility assessment: Based on the information and data collected during the firstconsultations and mission, the various analyses were conducted, including the analysis of the socio-economic impacts.

On March 22, 2018 the general layout of the project and the main objectives were discussed with Dr. Andrew Wyatt from IUCN via Skype. His comments regarding changing livelihoods and environmental issues were considered in this study.

After this draft report has been submitted, a second consultation including the final workshop will take place in April 2018. Results of the Feasibility Assessment will be presented to the GIZ Team and other stakeholders. Comments and recommendation based on the draft report will be incorporated in the presentation.

After comments have been received during the workshop, the Feasibility Assessment will be finalized.ThefinalreportisscheduledforMayandwill include all elements as outlined in the proposal.

11

The Mekong River is one of the largest river systems in the world with a length of 4,200 km and a catchment area of 795,000 km2. In Vietnam, it covers an area of around 40,500 km2. The Mekong Delta begins at Phnom Penh in Cambodia where the

4. DESCRIPTION OF THE PROJECT AREA

Figure 5: General map of the Mekong River in Vietnam

4.1 Topography

The project area is part of the Long XuyenQuadrangle. The ground level varies from 0.5 m to 1.8 m above sea level and the bottom elevation has a slope of less than 1%. The project area is part of the floodretentionareaintheLongXuyenQuadrangle.

4.2 Hydrology

The annual average temperature ranges from 26.5 to 27.3°C, the monthly temperature from 25.0 to 28.5°C. The annual average of the relative humidity lies between 82.2 and 85.7%. The general climate is characterized by two wind seasons, south-western

river is divided into Tien River and Hau River. The HauRiverflowsthroughtheVietnameseprovincesof An Giang, Can Tho, Vinh Long, Tra Vinh and Soc Trang (see Figure 5 below).

directions from May to October and north-eastern directions from November to April. The average rainfall in Rach Gia is 2,122 mm, in Ha Tien 1,991 mm, in Long Xuyen 1,511 mm and in Chau Doc1,306 mm. The rainy season lasts from May to November, and the dry season from December to April. The rainfall from July to October accounts for 60% and the rainfall from August to October for 50% of the annual precipitation. The highest evaporation of levels between 180-220 mm are reached in the months March, April and May. The evaporation decreases to 100-150 mm when the rainy season begins.

TheLongXuyenQuadrangleisaffectedtoalimiteddegree by the tidal cycle of both, the East Sea and the Gulf of Thailand. The tidal range of the semi-diurnal tide of the East Sea is between 3.5 and

12

4.0mintherivermouth.Itisalsoinfluencedbythemonthly neap-spring-cycle. The tidal wave of the East Sea enters deeply into Hau River and spreads widely in the networks of numerous channels. The tide of the Gulf of Thailand is a mixed semidiurnal tide with amplitude of 80 to 100 cm.

TheaveragetotalflowofTienRiverandHauRiverobserved at Tan Chau and Chau Doc is about 387 billion m3 annually and it is distributed unevenly throughout the year. Usually, in the early floodseason(JulytoAugust)thefloodlevelatChauDocis between 2.5 to 3.0 m to the end of July. The LongXuyenQuadrangle is influencedby thefloodwater levels in the Hau River and the flood waveapproaching from Cambodia. In August, the water levelatChauDocisbetween3.0to3.5 mandmostricefieldsinAnGiangProvinceareinundatedwithwater depths of 2.0 m. By the end of August, the water level at Chau Doc may further increase. The Cambodia flood can cause serious flooding at theLongXuyenQuadrangle,especiallyatthenorthareaofMacCanDungcanal,theflooddepthrangesfrom2.0 to 2.5 m, at some positions from 3.0 to 4.0 m (cf. Figure 7).

The middle period of the flood season is fromSeptembertoOctober.Atthistimethefloodreaches

a maximum depth, normally the water level at Chau Docis4.0mandthericefieldsarefilledwithwater.The flow rate can reach up to 25,500m3/s. From NovembertoDecemberthefloodrecedesandthewater level in the main rivers decreases. In total, the majorityofAnGiangprovinceisfloodedfrom3.0to4.0 m from August to end of December.

In December, when the water level decreases rapidly and little rainfall occurs, the dry season begins. The lowest average water level values are reached in the second half of April. The flow rate reaches aminimum of 2,340m3/s.

Figure6 indicateswater levels in thefloodseasonatXuanTostationandthusthewaterlevelsintheVinhTecanalthatareavailabletofillthereservoir.The water levels and temporal appearance vary over the years and thus influence theoperationof theprojected reservoir.

Groundwater in the Mekong Delta is quite abundant and used for several purposes: agricultural production, domestic use and industrial use. However, unsustainable exploitation leads to sinking groundwater levels, especially in the dry seasons in certain areas (e.g. Cu Lao Dung Island).

Figure6:WaterlevelinthefloodseasonatXuanTostation

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4.3. Geology and soil

4.3.1. Geotechnical parameters

Ingeneral,thesoilintheareaoftheplannedreservoirshowsverysmallpermeabilitycoefficientsandthusiscapable of retaining water as a reservoir. Table 1 summarizes important characteristic soil parameters that were derived from the executive summary of the project proposal and assessed based on a literature review.

Table 1: Soil parameters in the project area

Layer 1a Layer 1 Layer 2 Layer 2a

DescriptionVery loose to loose clay mix

organic

Very loose to loose organic

fat clay

Medium,stifftoverystiffclay

Medium dense clayey sand

Thickness [m] 1.8-2.2 3.3-6.0 3.4-4.0 >4.0

Soil class according DIN 18196 OT / (OU) OTTL / TM / (UL

/ UM)ST / ST*

Soil class according DIN 18301 BB 1 / BO 1 BB 1 / BO 1 BB 3 / BB 4 BN 1 / BN 2

Compactibility class accordingZTVE-StB-97

V3 V3 V3 V1 – V2

Unit weight according DIN 1055 [kN/m³] 14 (4) 14 – 16 (4-6)20 – 21 (10.5

– 11)18 – 20 (10

– 12)

Friction angle according DIN 1055 [°] 15 15 – 20 22.5 – 27.5 25 30

Cohesion c´ according DIN 1055 [kN/m²] 0 0 15 – 25 5 – 10

Elastic modulus [MN/m²] 0,5 – 3 1 – 5 2,5 – 10 20 40

Permeability according DIN 18130 [m/s] < 10-8 < 10-8 <10-8 10-7 – 10-4

Figure7:FloodflowdirectionintheMekongDeltaduringfloodintheyear2000

14

Assuming those soil parameters and the dimensions of the proposed embankments, a rough calculation of the setting was executed. Setting in the dimensions ofseveraldecimetresismostlikelyandwillinfluenceconstructions and construction costs as well as the maximum volume of the reservoir.

4.3.2. Soil chemistry

In southern Vietnam, 1.6 million ha (47 %) of Long XuyenQuadrangle,PlainofReeds,WestHauRiver,and a large part of Ca Mau peninsula are mainly characterized by acid sulphate soils. They have high iron sulphide concentrations and are very sensitive tofluctuationsinthegroundwatertableandtheriverdischarge (Tuan and wyseure, 2016). Acid sulphate soils are divided into two subgroups: active and potential sulphate soils. Active sulphate soils are concentrated in areas with poor drainage conditions. In the coastal belt, there are predominantly saline acid sulfate soils (Truong 2002). Their main characteristic is that there is potential to develop high levels of acidity upon exposure to oxygen (hashimoTo, 2001). Potential sulphate soils occur in an area of 613,000 ha, especially in drainage areas. 72 % of these areas are rice paddies and 5 % of other agricultural use. Possible reasons for intrusion of air are groundwater

removal, establishing of drainage systems, and groundwater interception. These interventions are responsible for enormous environmental and socio-economic changes which arise the current environmental problems.

Salineintrusionandsoilacidificationareincreasedbystormandflooddamages,botheventsintensifiedsince 1996. Accordingly, important natural functions of the primordial ecosystems including biodiversity got lost to a significant extent (ni eT al. 2016). A study of denT (1986)figuredout thatacidsulphatesoils pose serious chemical, physical, and biological problems. Especially, the oxidation of pyrite leads to aluminiumtoxicityandacidification,sincehydrogensulfide and iron arise. On these affected areas, aspecific technical management will be necessaryfor restoringasufficientperformanceofcropping.Therefore, it is important to transfer and to develop new agricultural practices that are adapted to the special soil characteristics. In the following consequencesofsoilacidificationaresummarized:Clay minerals may be destroyed and aluminium (Al) minerals will be dissolved. Furthermore, a lack of nutrients due to wash-outs will arise. In addition, soil pH-values will decrease and a disposal of heavy metals will occur. Increasing wash-outs lead to an acidificationofgroundwater,andofsurfacewater.

15

The general idea of the proposed investment is to fill up the reservoir beginning from themiddle ofthefloodseasonapproximately inSeptemberandOctober until the water levels in the Hau River and the Vinh Te canal begin to decrease. Times can vary significantly.ThisprocedurewillalsoallowremovingthepeakofthefloodwavefromtheVinhTecanal.

The total area in the original project layout is 3,050 ha, and it is surrounded by a total embankment length of 37.40 km. The proposal uses ground level elevationofthereservoirof0.5to0.8 m.However,the given geographic information system data shows ground level elevation of 1.1 to 1.6 m with a mean elevation of 1.26 m. These values are considered as reliable and are used for the following calculations. In the proposal dredging was proposed to lower the elevation to 0.00 m. Assuming a water level of 4.5 m the total volume of the reservoir would be 137.25·106 m³ [= 3,050 ha · 10,000 m²/ha · (4.5 m - 0.0 m)]. The water volume of the canals is excluded from this volume. It is assumed that an additional volume of 50.00·106 m³ is pumped from the Vinh Te canal into the reservoir in the dry season. This volume fills up the water volume in the reservoir and compensates removed water, and thus increases the total time-integrated volume of the reservoir. According pumps will be installed at the sluice gates at the Vinh Te canal that will replace the rubber dams. Six pumps with capacity of 2 m³/s each were proposed. Pumping during approximately 48 days is necessary to reach this volume. The expected total areaofricefieldsthatbenefitfromsupplyfromthereservoir is 30,000 ha.

5. DESCRIPTION OF THE PROPOSED PROJECT

The operation of the sluice gates of the planned reservoir is key for water management. As illustrated by Figure 8, six sluice gates are foreseen in the original design. It was proposed that all sluice gates of the proposed reservoir including the downstream sluice gates 3-6 will be open at that time. It might be necessary to close sluice gates 3-6 to reach to required water level of 4.50 m. This depends on the hydraulic capacityof thesluicegatesand theflowthrough the reservoir.Maximumflow through thesluice gates 1 and 2 must be checked. When the water levels in the Hau River and the Vinh Te canal are falling, all sluice gates are closed to keep the design water level. If the design water level of 4.50 m has not been reached in the reservoir, water can be pumped into the reservoir – approximately between November and February. Potential pumping depends on the water levels in the Vinh Te canal.

In the dry season it is envisaged to keep the water level high as long as possible. Pumping is used to maintain the water level to compensate water usage (andevaporation/infiltration).WhenthewaterlevelsintheVinhTecanalarenotsufficientanymoreforpumping, water levels in the reservoir will decrease due to water usage. Sluice gates 3-6 will be open during that time to supply downstream areas with fresh water. The reservoir should be managed in a way so that it still holds water at the beginning of the floodseason.During5to7monthsthewaterlevelin the reservoir will be 4.50 m or slightly lower, and thefieldscannotbeusedduringthattime.

16

1

2

3

4

5 6

Figure 9: Overlay of the reservoir area with aerial photo

Figure 8: Projected reservoir with sluice gates 1-6

17

Based on the initial desk study and the firstconsultancy the main topics have been identifiedthat need to be clarified and considered in thefeasibility study. The interdependency between several topics requires a multi-iterative approach.

Hydrologic and hydraulic simulations are performed using existing models operated by the national consultants. Input data for the simulations, the geo-engineering proofs, the environmental impact assessment including the Tra Su forest as well as data for the socio-economic assessment including different livelihood models and the cost-benefit-analysis were taken from previous studies. During the consultation meetings, involved provinces

agreed to provide the consultant team with latest updated data, especially on land use, agriculture/aquaculture, and demographics.

6.1 Technical Feasibility

6.1.1 General hydrology

Generally, the operation of the reservoir can be described according to the following simplifiedscheme. It was derived from the proposed operation described in section 5 above.

6. FEASIBILITY ASSESSMENT OF THE PROPOSED PROJECT

Figure10:Simplifiedhydrologicalscheme

(red=closed, green=open, shaded=pumping, =rising water level, =falling water level)

The fill-up of the reservoir through sluice gates 1and 2 with water from the Vinh Te canal is essential for the operation of the reservoir. Floodwater from Cambodia at early stages of the flood maycontain higher concentrations of chemical fertilizers and pesticides. Storing this floodwater is notrecommendable without further analysis of the water quality. This might reduce the available water volume but is considered as negligible for now. Figure6 indicateswater levels in thefloodseasonin the Vinh Te canal. The water levels and temporal appearancevaryovertheyearsandthusinfluencethe amount of water that needs to be pumped into the reservoir. In the following calculation it is assumed that the water volumes in the Vinh Te canalaresufficienttofill-upthereservoirbetweenAugust and November.

However,differentscenarioswithvaryingdischargerates need to be considered. The Vietnamese Ministry of Natural Resources and Environment (MONRE) defined some future climate changescenarios for Vietnam. The scenarios set a range of input parameters for current and future water management projects. Rather than using fixedvalues, computations should be performed with minimum and maximum values for future river discharges, sea level rise, saline intrusion, or rainfall (mekong delTa plan 2013). Table 2 shows the key parameters of a moderate and a heavy level scenario regarding the climate change expected for the years 2050 and 2100.

Month/Sluice 1 2 3 4 5 6 7 8 9 10 11 12123456WL[m]

–4.50

4.50–

4.50–

4.50

18

Table 2: Characteristics of two climate change scenarios

Moderate scenarios Heavy scenarios

2050 2100 2050 2100

Increase of wet season flow No change 10 % 0 – 10 % 20 – 50 %

Increase of wet season rainfall 0 – 5 % 5 – 10 % 10 – 20 % 10 – 30 %

Dryseasonflow+/- 5 %

(higher or lower)5 % higher15 % lower

10 – 30 %lower

30 – 60 %lower

Decrease of dry season rainfall 0 – 10 % less 5 – 15 % less 10 – 20 % less 20 – 40 % less

Increase of salinity intrusion slight moderate moderate dramatic

Sea level rise 20 – 30 cm 57 – 73 cm 40 – 60 cm 78 – 95 cm

Source: Adapted from Mekong Delta Master Plan 2013

6.1.2 Location and dimensions

In the original proposal, the Tra Su melaleuca forest was included in the project area. However, we recommend that due to ecological reasons, the Tra Su forest should not be included in the reservoir area. It is considered as most likely that a long-lasting inundation of the Tra Su forest will seriously harm it. If the forest is excluded from the area, it decreases to 2,175 ha. The total length of embankments in this case is 20.94 km. This is a reduction of the reservoir area of approximately 29%. The resulting volume is 97.875·106 m³ [= 2,175 ha · (4.50 m - 0.00 m)], instead of 137.25 106 m³. Figure 11 shows the resulting area and Figure 12 a scheme of the reservoir including the relevant elements.

Furthermore, dredging is seen critically and should be avoided due to ecological reasons (e.g. mobilization of pollutants, massive earth-moving) andfinancialreasons(costsfordredgingandfollow-up costs). Without dredging the total volume will further decrease to 70.470 106 m³ [=2,175 ha · (4.50 m - 1.26 m)]. It is assumed that the area of rice fields that benefit from supply from the reservoirwill decrease linearly to the reduction of the total volume (0,51 · 30,000 ha = 15,300 ha).A further alternative design would be to include areas south of the Tra Su forest resulting in a total area of 3,040  ha (Figure 13). For this alternativeoption, further constructions such as a hydraulic bypass (gravityfloworpressurepipeline) fromthearea north of the Tra Su forest to the area south of the forest is required. This induces higher costs but increases the reservoir area in the consequence the potentialbenefits.

19

Figure 11: Area of the reservoir without the Tra Su forest

Figure 12: Scheme of the reservoir

20

Figure 13: Alternative reservoir area with additional area south of the excluded Tra Su forest

Based on the above description there are basically 4 alternatives:

1. Original design including Tra Su forest, area 3,050 ha, including dredging

2. Original design including Tra Su forest, area 3,050 ha, no dredging

3. Adapted design without Tra Su forest, area 2,175 ha, including dredging

4. Adapted design without Tra Su forest, area 2,175 ha, no dredging

ThefifthalternativeincludingareassouthoftheTraSuforestresultsinatotalareaof3,040 ha,andthusiscomparabletotheareaoftheoriginaldesign.Thevariousalternativesresultindifferentmaximumstoragevolumes according to Table 3.

Table3:Volumesofdifferentdesignalternatives

Volumesofdifferentalternatives No dredging Dredging

Original design 98.820 106 m³ 137.250 106 m³

Original design without Tra Su forest 70.470 106 m³ 97.875·106 m³

Original design without Tra Su forest plus areas south of Tra Su forest 98.496 106 m³ 136.800 106 m³

Ifthereservoiriffilledwithfloodwater,acertainsedimentationofthesuspendedsedimentswilloccurduetothe low currents velocities within the reservoir. Concentrations of total suspended sediments in the Mekong and its tributaries and channels can be assessed e.g. based on Renaud & Kuenzer (2012) with 100-200 mg/l within the floodperiod.Assuming that the sediment loadnear the riverbed is not transported into thereservoir (e.g. by constructional elements such as lock sills) those concentrations lead to sedimentation of less than 0.01 m. Thus, sedimentation is in the range of the surveying precision and can be neglected.

21

Figure 14: Alternative reservoir area with additional area south of the excluded Tra Su forest

Theresultingdifferencebetweenevaporationandprecipitationrequirespumpingifthewaterlevelshouldbekept on a constant level. The required pumping rate depends on the area of the reservoir. Figure 15 indicates thatpumpingissignificantandsoarepumpingcostsifthewaterleveliskeptonaconstantlevel.Ifnowaterispumpedintothereservoir,duetofinancialaspectsorlackofwaterintheVinhTecanal,thewaterlevelinthe reservoir will decrease by the level indicated in Figure 14.

6.1.3 Assessment of evaporation

The calculation of the evaporation has been done according to Penman (LECHER et al., 2015). The calculation and required assumptions are displayed in the Annex. Figure 14 shows the results of the calculation of the evaporation in mm/month, and additionally the precipitation in the project area.

Month

Month

Pum

ping

Rat

e [m

3 /s]

Evap

ora�

on/P

reci

pita

�on

[mm

/mon

th]

1

250

200

150

100

50

0

2.5

2

1.5

1

0.5

0

2 3 4 5 6 7 8 9 10 11 12

1 2 3 4 5 6 7 8 9 10 11 12

Evapora�on

Precipita�on

Evapora�on according to Penman

Required pumping to balance evapora�on

Area 3,050 ha

Area 2,175 ha

Month

Month

Pum

ping

Rat

e [m

3 /s]

Evap

ora�

on/P

reci

pita

�on

[mm

/mon

th]

1

250

200

150

100

50

0

2.5

2

1.5

1

0.5

0

2 3 4 5 6 7 8 9 10 11 12

1 2 3 4 5 6 7 8 9 10 11 12

Evapora�on

Precipita�on

Evapora�on according to Penman

Required pumping to balance evapora�on

Area 3,050 ha

Area 2,175 ha

Figure 15: Required pumping rates to balance evaporation

22

6.1.4 Assessment of infiltration

Generally,thecharacteristicsoilparametersintheprojectareashowverysmallpermeabilitycoefficientsandthusthesubsoilissuitabletoretainwaterinthereservoir.However,infiltrationaccordingtoDarcy’sfilterlawis calculated to verify the general assumption.

TheinfiltrationrateisQ=v·Awithafiltervelocityv=kf · I.

The according kf value is considered to be 1 · 10-8 m/s for clay.

ThehydraulicgradientIisdefinedasI=z/ls whereas ls is the distance from the bottom of reservoir to ground water layer and z is the water depth in the reservoir

Basedonthecalculation, infiltrationisupto0,015m³/m²andmonthdependingonthewaterlevel inthereservoir.Higherwaterlevelsincreasetheinfiltrationrate(Figure16).

If the water level in the reservoir should be kept in balance, additional pumping is required. Required pumping ratesareindicatedinFigure16.Incomparisontotheeffectsofevaporation,lossofwaterduetoinfiltrationcan be neglected.

Figure16:Infiltrationratesandrequiredpumpingtobalanceinfiltration

Water level [m]6 5 4 3 2 1 0

0

0.04

0.08

0.12

0.16

0

0.004

0.008

0.012

0.016 0.2

Infil

tra�

on Q

[m3 /m

2 mon

th]

Pum

ping

Q [m

2 /s]

Infiltra�on

Pumping Q [m2/s] at 3050 haPumping Q [m2/s] at 2175 ha

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 28

Assessment of infiltration Generally, the characteristic soil parameters in the project area show very small permeability coefficients and thus the subsoil is suitable to retain water in the reservoir. However, infiltration according to Darcy’s filter law is calculated to verify the general assumption. The infiltration rate is Q = v · A with a filter velocity v = kf · I. The according kf value is considered to be 1 · 10-8 m/s for clay. The hydraulic gradient I is defined as I = z / ls whereas ls is the distance from the bottom of reservoir to ground water layer and z is the water depth in the reservoir Based on the calculation, infiltration is up to 0,015 m³/m² and month depending on the water level in the reservoir. Higher water levels increase the infiltration rate (Figure 16). If the water level in the reservoir should be kept in balance, additional pumping is required. Required pumping rates are indicated in Figure 16. In comparison to the effects of evaporation, loss of water due to infiltration can be neglected.

Figure 16: Infiltration rates and required pumping to balance infiltration

Water inlet The water inlet from the Vinh Te canal is essential for the feasibility of the proposed reservoir. Although additional pumping is possible and will be required, pumping costs should be mini-mized. The general goal should be to increase gravity flow through the projected sluice gates at the Vinh Te canal as much as possible. The controlled flow through the sluice gate was calculated according to Toricelli:

𝑄𝑄 = µ ∗ 𝑠𝑠 ∗ 𝑏𝑏𝑔𝑔 ∗ √2 ∗ 𝑔𝑔 ∗ ℎ𝑅𝑅

whereas: hR = water level in the Vinh Te canal µ = 0,6 (empirical coefficient, typical value for sharp-edged weirs) 𝑠𝑠 = opening of sluice gate [m]

6.1.5 Water inlet

The water inlet from the Vinh Te canal is essential for the feasibility of the proposed reservoir. Although additional pumping is possible and will be required, pumping costs should be minimized. The general goalshouldbetoincreasegravityflowthroughtheprojected sluice gates at the Vinh Te canal as much as possible.

The controlled flow through the sluice gate wascalculated according to Toricelli:

whereas:

y hR = water level in the Vinh Te canal

y µ = 0,6(empirical coefficient, typical value forsharp-edged weirs)

y s = opening of sluice gate [m]

y bg = width of the sluice gate

23

Figure 17 displays the input through one sluice gate that will replace one of the rubber dams. In total two sluice gates are projected at the location of the two rubber dams. Their width was considered as 40 m. Their base was considered to be at an elevation of 1.50 m.

Evenincaseofscenarioswithlowerpeakwaterlevelsinthefloodseasonaround2m(cf.Figure6)gravityflowthroughtheprojectedsluicegateswithawidthof40mandabasewithanelevationof1.50missufficient.

Figure17:Inletflowthroughonesluicegatewiththewidthof40mdependingon the water level in the Vinh Te canal

6.1.6. Water discharge

The water volume that is used for fresh water supply must be led from the reservoir to the surrounding areas via the main sluice gates in the embankments that form the border of the reservoir. Thus, the maximum discharge through the sluice gates 3, 4, 5 and 6 is a key parameter.

This controlled discharge is also calculated according to Toricelli:

whereas:

y hR = 4,5m - maximum water level in the reservoir

y µ=0,6(empiricalcoefficient,typicalvalueforsharp-edgedweirs)

y s = opening of sluice gate [m]

y bg = Width of the sluice gate

The discharge through the 4 sluice gates and the total discharge through all sluice gates is displayed In Figure 18.Itissufficienttoensuretherequiredflowtosupplythesurroundingareas.Generallyitwouldbefeasibleto reduce the width of the sluice gates or even to leave one sluice gate out, e.g. sluice gate 5.

0

600

500

400

300

200

100

Qin

[m3 /s

]

00.5 1.5 2.5 3.51 2

s (opening of sluice gate) [m]3 4

2.00 m2.50 m3.00 m3.50 m4.00 m4.50 m

Water level Vinh Te canal

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 29

𝑏𝑏𝑔𝑔 = width of the sluice gate

Figure 17 displays the input through one sluice gate that will replace one of the rubber dams. In total two sluice gates are projected at the location of the two rubber dams. Their width was considered as 40 m. Their base was considered to be at an elevation of 1.50 m. Even in case of scenarios with lower peak water levels in the flood season around 2 m (cf. Figure 6) gravity flow through the projected sluice gates with a width of 40 m and a base with an ele-vation of 1.50 m is sufficient.

Figure 17: Inlet flow through one sluice gate with the width of 40 m depending on the water level in the Vinh Te canal

Water discharge The water volume that is used for fresh water supply must be led from the reservoir to the surrounding areas via the main sluice gates in the embankments that form the border of the reservoir. Thus, the maximum discharge through the sluice gates 3, 4, 5 and 6 is a key parameter. This controlled discharge is also calculated according to Toricelli:

𝑄𝑄 = µ ∗ 𝑠𝑠 ∗ 𝑏𝑏𝑔𝑔 ∗ √2 ∗ 𝑔𝑔 ∗ ℎ𝑅𝑅

whereas: ℎ𝑅𝑅 = 4,5 𝑚𝑚 – maximum water level in the reservoir µ = 0,6 (empirical coefficient, typical value for sharp-edged weirs) 𝑠𝑠 = opening of sluice gate [m] 𝑏𝑏𝑔𝑔 = Width of the sluice gate

24

Figure 18: Discharge through the projected sluice gates

Incaseofemergency,suchasabankfull/maximumwaterlevelof5.50minthereservoir,forfloodreleasethedischargethroughacompletelyopenedsluicegateneedstobechecked.Table4indicatesthemaximumflowrates. In case of the original design with an area of the reservoir of 3,050 ha the water could be decreases by 0.37 m per hour, and by 0.51 m per hour n case of an area of 2,175 ha respectively. This is considered as sufficient.

Table4:Maximumflowthroughthesluicegatesincaseoffloodrelease

Sluice gate Width [m] Qmax [m³/s]

Tra Su 1 40 1,240

Nhon Thoi 10 310

Kenh Ranh 20 620

Kenh Dao 30 930

Total 100 3,100

According to Toricelli the current velocity at the outlet of the sluice gate is is

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 31

According to Toricelli the current velocity at the outlet of the sluice gate is 𝑣𝑣 = √2 ∗ 𝑔𝑔 ∗ ℎ𝑅𝑅, and thus up to 9.4 m/s at an upstream water level of 4.5 m. This very high outflow velocities induce massive erosion and scouring and thus require a wide and massive absorption pool. Absorption pools are a constructional measure to dissipate the energy of the water. They gen-erate a controlled hydraulic jump from supercritical to subcritical flow. By this, the bottom is protected against erosion and scouring is prevented. The material has to be resistant against erosion, for example concrete, stones or gabions. If an absorption pool is not applied, erosion at the outlet can endanger the stability of the sluice gate.

Figure 19: Absorption pool with hydraulic jump Source: http://docplayer.org/docs-images/51/28145902/images/15-0.png

Hydrological model The results of the previous sections are summarized in a simplified hydrological model. It con-siders the following processes according to the previous descriptions:

precipitation, evaporation, infiltration, pumping (considering 6 pumps with an capacity of 2 m³/s each), filling through sluice gates 1 and 2, discharge through sluice gates 3, 4, 5 and 6 for fresh water supply.

The calculation has been done by several iterations using start values (water level at a certain date, e.g. end of dry season) and end values (water level at a certain date) and different bound-ary conditions (basically geometry including dyke heights). Figure 20 shows the results of the model (water levels, potential fresh water supply) for the various alternatives assuming a constant use of the stored water. The reservoir is filled up with gravity flow from the Vinh Te Canal is far as possible, and pumping is used to maintain the water level until the fresh water supply starts. Water levels and according water depths are 1.00 m or higher if the water supply should be possible during the entire dry season. If the summer rice crop should be kept, the water level from April to July must be significantly below 1 m. During that time no water supply would be possible, and this would significantly limit the function of the reservoir.

, and thus up to 9.4m/satanupstreamwaterlevelof4.5m.Thisveryhighoutflowvelocitiesinducemassiveerosionandscouring and thus require a wide and massive absorption pool.

Absorption pools are a constructional measure to dissipate the energy of the water. They generate a controlled hydraulic jump from supercritical to subcritical flow. By this, the bottom is protected againsterosion and scouring is prevented. The material has to be resistant against erosion, for example concrete, stones or gabions. If an absorption pool is not applied, erosion at the outlet can endanger the stability of the sluice gate.

3000

2000

1000

0

0 1 2 3 4 5

Tra su 1 (40 m)Nhon Thoi (10 m)Kenh Ranh (20 m)Kenh Dao (30 m)Total

s (opening of sluice gate) [m]

Q [m

3 /s]

25

Figure 19: Absorption pool with hydraulic jump

6.1.7 Hydrological model

The results of theprevious sections are summarized in a simplifiedhydrologicalmodel. It considers thefollowing processes according to the previous descriptions:

y precipitation,

y evaporation,

y infiltration,

y pumping (considering 6 pumps with an capacity of 2 m³/s each),

y fillingthroughsluicegates1and2,

y discharge through sluice gates 3, 4, 5 and 6 for fresh water supply.

The calculation has been done by several iterations using start values (water level at a certain date, e.g. end ofdryseason)andendvalues (water levelatacertaindate)anddifferentboundaryconditions (basicallygeometry including dyke heights).

Figure 20 shows the results of the model (water levels, potential fresh water supply) for the various alternatives assumingaconstantuseofthestoredwater.ThereservoirisfilledupwithgravityflowfromtheVinhTeCanalis far as possible, and pumping is used to maintain the water level until the fresh water supply starts.

Water levels and according water depths are 1.00 m or higher if the water supply should be possible during the entire dry season. If the summer rice crop should be kept, the water level from April to July must be significantlybelow1m.Duringthattimenowatersupplywouldbepossible,andthiswouldsignificantlylimitthe function of the reservoir.

26

Figure20:Waterlevelsandfreshwaterusagefordifferentalternatives

MonthEMPTYING FILLING PUMPING

Wat

er L

evel

[m]

1

0

1

2

3

4

5

Usa

ge [m

3 ]

-5E+006

0

-1E+007

-1.5E+007

-2E+007

-2.5E+007

-3E+007

2 3 4 5 6 7 8 9 10 11 12

Month1 2 3 4 5 6 7 8 9 10 11 12

Dredging

No dredging

Dredging, 3,050 haDredging, 2,175 haNo dredging, 3,050 haNo dredging, 2,175 ha

27

6.1.8 Summary of structural measures

Table 5 indicates the key facts such as dimensions of the proposed reservoir and the according structural measures.

Table 5: Key facts of the proposed reservoir

No. Item Unit Parameter Remark1 Key parametersa Area of reservoir ha 2,175

b Existing ground level of project area

m +1.1 to +1.6 (mean 1.26)

c Bottom elevation of proposed reservoir

m +1.1 to +1.6 No dredging

d Water level m 2.65 to 4.50

e Water depths m 1.00 to 3.24

f Maximum total volume of reservoir

m3 70.470 106

g Max. volume of water pumped from Vinh Te canal to the reservoir

m3/s 12

h Expected area of irrigation ha 15,300

2 Parameters of workNo. Item Unit Existing

ConditionsMeasures Remark

1 The west embankment – Tra Su canal embankment segment 1: Not upgradeda Length m 2,000 No measures necessary No costsb Width of surface m 6.00c Top elevation m 5.50d Bottom elevation m 0.80e Slope - 1:1.5f Slope protection - Gabionsg Surface - Asphalt road

2 The west embankment – Tra Su canal embankment segment 2: New constructiona Length m 2,000

b Width of surface m 6.00

c Top elevation m 5.50+0.60

d Settlement m 0.57

e Bottom elevation m 1.00 0.80f Slope m 1:1.5

g Slope protection - Gabions

h Surface - Paved road

28

3 The west embankment – Tra Su canal embankment segment 3: Upgradeda Length m 3,700

b Width of Surface m 6.00

c Top elevation m 5.00 +0.50d Bottom elevation m 1.00 0.80e Slope - 1:1.5

f Slope protection - Gabions

g Surface Paved road

4 The south embankment: new constructeda Length m 3,000

b Width of surface m 6.00

c Top elevation m 5.50 + 0.60

d Settlement m 0.57

e Bottom elevation m 0.80

f Slope - 1:1.5

g Slope protections - Gabions

h Surface - Paved road

5 The east embankment – Tha La canal embankment: Not upgradeda Length m 8,600 No measures necessary No costsb Width of surface m 6.00c Bottom elevation m 0.80d Slope - 1:1.5e Slope protection - Gabionsf Surface - Asphalt road6 The north embankment – Vinh Te canal embankment: Not upgradeda Length m 1,800 No measures necessary No costsb Width of surface m 6.00c Bottom elevation m 0.90d Slope -- 1:1.5e Slope protection - Gabionsf Surface - Asphalt road7.1 Sluice gate: Kenh Daoa Width of water body m 30.00

b Bottom elevation of sluice gate

m -2.00

c Mechanical gate m 3 x (10 x 6.5)

Operating by electric winch

29

d Absorption pool m Length 20 m, Width 30 m

7.2 Sluice gate: Tra Su 1a Width of water body m 40.00

b Bottom elevation of sluice gate

m -2.00

c Mechanical gate m 4 x (10 x 6.5) Operating by electrical winch

d Absorption pool m Length 20 m, Width 40 m

7.3 Sluice gate: Nhon Toia Width of water body m 10.00

b Bottom elevation of sluice gate

m -2.00

c Mechanical gate m 10 x 6.5 Operating by electrical winch

d Absorption pool m Length 20 m, Width 10 m

7.4 Sluice gate: Kenh Ranha Width of water body m 20.00

b Bottom elevation of sluice gate

m -2.00

c Mechanical gate m 2 x (10 x 6.5) Operating by electrical winch

d Absorption pool m Length 20 m, Width 20 m

8 Pumping stationa Capacity m3/s 6 · 2 m²/s

6.1.9 Geotechnical engineering

For geotechnical calculations and proofs, information about the subsoil is required. Since only very limited data on the subsoil in the western part of the reservoir are available, characteristic soil parameterswerederivedfromtheexecutivesummary.Valuesgiven infigures41,43and44ofthe executive summary were used to compute according values of the subsoil underneath the embankments to be upgraded. Table 6 summarizes those assessed parameters representing conservative values.

Table 6: Values of the assumed layering of the subsoil,

Soilγ

[kN/m³]γ’

[kN/m³]ϕ[°]

c[kN/m²]

Es[MN/m²]

Layer

14.00 4.00 15.00 0.00 0.50 1a (clay mix organic)

14.00 4.00 15.00 0.00 1.00 1 (fat clay)

20.00 10.50 22.50 15.00 2.50 2 (clay)

18.00 10.00 25.00 5.00 20.00 2a (clayey sand)

Note: γ unit weight; γ’ buoyant unit weight; ϕ inner angle of friction; c cohesion and ES elastic modulus

30

Table7:Partialfactorsonactionsortheeffectofactions

Action SymbolA1

SetA2 A2

PermanentUnfavourable

YG

1.35 1

Favourable 1 1

VariableUnfavourable

YQ

1.5 1.3

Favourable 0 0

Table 8: Partial resistance factors for spread foundations

Resistance SymbolSet

R1 R2 R3

Bearing YRv 1 1.4 1

Sliding YRh 1 1.1 1

Table 9: Partial factors for soil parameters

Soil parameter SybolValue

M1 M2

Shearing resistance Yϕ1 1 1.25

Effectivecohesion Yc 1 1.25

Undrained strength Ycu 1 1.4

Unconfinedstrength Yqu 1 1.4

Effectivecohesion Yc 1 1.4

Weight density Yy 1 1

1 This factor is applied to tan ϕ'

Several geotechnical proofs must be provided for the embankments. If a load is applied on the ground,itincreasestheverticaleffectivestress.Thisstress increases the vertical strain in the soil. And this increase in vertical strain causes the ground to move downward. This downward movement of the ground is defined as settlement and resultsin a loss of the overall height of the construction. This settlement can be compensated by a super-elevation of the crest height.

To check the safety of the slopes of the embankments, calculations are made to determine the shear stresses developed along the most likely rupture surface and compared with the shear strength of the soil. This process is called slope stability analysis. The most likely rupture surface is the critical surface that has the minimum factor of safety. Seepage through the slope and the choice of potential slip surface add to the complexity of the problem. If the pressure induced by the dead weight

of the embankment and live load on the according crest is too large, the base of the embankments or the slope can collapse.

For the calculation of settlement, slope and base failure, the software GGU-Footing is used. The software utilizes the standards of the Eurocode 7 (EC 7), which is the geotechnical part within a set of European Standards (EN), providing a common approach for civil engineering works. EC 7 is providing a concept of partial safety factors depending on the state of the system. It is based on the principle that actions have to be smaller or equal to resistances of the design case. To ensure the reliability of the design, partial factors are applied to actions (A), resistances (R) or material properties (M). Actions can be foundation load or foundation self-weight, in this case the weight of the embankment, whereas

the according resistance is the soil resistance. The partial safety factors are shown in the following tables.

31

Exemplarily, the second segment of the Tra Su canal embankment was used for the calculations (cf. Figure 21).Thispartinthewesternpartofthefloodreservoirwillbenewlyconstructed.

Figure 21: Typical cross section of the west embankment

The load of the embankment is calculated applying the specific weight of organic clay mix (layer 1a) that is considered to be used as construction material for the embankment. This is done based on the geometry of the embankment with a cross sectional area of 52.65 m² per running meter. After multiplication of the cross sectional area with the

specificweightof14kN/, a loadof737.10kNperrunning meter length are obtained. Regarding the large dead weight of the embankment, the weight of the structure of the road and the geotextiles can be neglected. Figure 22 shows the stress curve and the presumed layering below the embankment.

32

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 38

The load of the embankment is calculated applying the specific weight of organic clay mix (layer 1 a) that is considered to be used as construction material for the embankment. This is done based on the geometry of the embankment with a cross sectional area of 52.65 m² per running meter. After multiplication of the cross sectional area with the specific weight of 14 kN/m3, a load of 737.10 kN per running meter length are obtained. Regarding the large dead weight of the embankment, the weight of the structure of the road and the geotextiles can be neglected. Figure 22 shows the stress curve and the presumed layering below the embankment.

Figure 22: Stress curve below the embankment.

In a first step a calculation of the settlement of the embankment is performed, which is found to be 57 cm. In this case, base failure is not relevant. The following table shows the results of the calculation.

Figure 22: Stress curve below the embankment.

Inafirststepacalculationofthesettlementoftheembankmentisperformed,whichisfoundtobe57cm.Inthis case, base failure is not relevant. The following table shows the results of the calculation.

33

Table 10: Geotechnical calculation regarding setting and base failure

Partial safety (ground failure) γGr = 1.40

σ0f,k / σ0f,d = 157.37 / 112.41 kN/m²

Rn,k = 2485620.21 kN

Rn,d = 1775443.01 kN

Vd = 1.35 · 995085.00 + 1.50 · 0.00 kN

Vd = 1343364.75 kN

μ (parallel to x) = 0.757

cal ϕ = 20.0 °

ϕ reduced, because of 5° condition

cal c = 5.98 kN/m²

cal γ2 = 6.18 kN/m³

cal σ0 = 0.00 kN/m²

cal β = 10.00 °

Lower edge of logarithmic spiral = 13.60 m below ground surface

Length of logarithmic spiral = 47.03 m

Area of logarithmic spiral = 310.51 m²

Load bearing factors (x):

Nc0 = 14.82; Nd0 = 6.38; Nb0 = 1.96λ

Shape factors (x):

νc = 1.004; νd = 1.003; νb = 0.997

Geländeneigungsbeiwerte (x):

λ c = 0.859; λ d = 0.692; λ b = 0.575

Settling due to total loads:

Limiting depth tg = 16.36 m below ground surface

Settlement (mean of all corner points)

Settlement of corner points

Top left = 56.95 cm

Top right = 56.95 cm

Lower left = 56.95 cm

Lower right = 56.95 cm

Torsion (x) (corner point) = 0.0

Torsion (y) (corner point) = 0.0

Proof EQU (equilibrium):

Crucial: width of foundation:

Mstb = 995085.0 · 11.70 · 0.5 · 0.90 = 5239122.5

Mdst = 0.0

μEQU = 0.0 / 5239122.5 = 0.000

Basis of calculation:

Standard: Eurocode 7

Base failure formula of DIN 4017:2016

Partial safety concept (EC 7)

γGr = 1.40

γG = 1.35

γQ = 1.50

Limit state EQU (equilibrium)

γG,dst = 1.10

γG,stb = 0.90

γQ,dst = 1.50

Ground surface = 1.00 m

Foundation level = 1.00 m

Ground water = 1.00 m

Limiting depth with p = 20.0 %

Results isolated foundation:

Loads = persistent / transient

Vertical load Fv,k = 995085.00 / 0.00 kN

Horizontal load Fh,x,k = 0.00 / 0.00 kN

Horizontal load Fh,y,k = 0.00 / 0.00 kN

Momentum Mx,k = 0.00 / 0.00 kN·m

Momentum Mx,k = 0.00 / 0.00 kN·m

Length a = 1350.00 m

Width b = 11.70 m

Under permanent loads

Eccentricity ex = 0.000 m

Eccentricity ex = 0.000 m

Resultant in the 1. core

Length a’ = 1350.00 m

Width b’ = 11.70 m

Under total loads:

Eccentricity ex = 0.000 m

Eccentricity ey = 0.000 m

Resultant in the 1. core

Length a’ = 1350.00 m

Width b’ = 11.70 m

Base failure:

Punching examined, but not crucial.

34

Multiplicationoftheheightoftheembankmentof4.5mwiththespecificdensityof14kN/m3 results in a pressure of 63 kN/m2, and of 88.2 kN/m2 respectively, if the partial safety factor γGr = 1.4 is applied. If the limit state is exceeded, base failure occurs as displayed in Figure 23. Exemplarily, the mean slope of the bottom of the reservoir is assumed to be 10°.

Figure 23: View of the circular slip, when the limit state is exceeded.

To assess the maximum possible height of the embankment, a calculation is done to reveal the critical state when base failure is going to occur. A stress of σR,d = 112.4kN/m2 is found to be relevant.

Table11:Resultsofthecalculationtofindthelimitedstate

If the limit load of kN/m2 is divided by the safety factor of 1.4 the resulting pressure is 80.29 kN/m2. Divided bythespecificweight14kN/m3, a maximum height of the embankment of 5.70 m is obtained.

In an iterative process, a maximum slope of the bottom of the reservoir or the canal of 19.9° next to the embankment has been found to be relevant. Figure 24 shows the mode of failure if the slope is exceeded.

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 41

Figure 23: View of the circular slip, when the limit state is exceeded.

To assess the maximum possible height of the embankment, a calculation is done to reveal the critical state when base failure is going to occur. A stress of 𝑅𝑅,𝑑𝑑 = 112.4 kN/m2 is found to be relevant.

Table 11: Results of the calculation to find the limited state

If the limit load of 112.4 kN/m2 is divided by the safety factor of 1.4, the resulting pressure is 80.29 kN/m2. Divided by the specific weight 14 kN/m3, a maximum height of the embankment of 5.70 m is obtained. In an iterative process, a maximum slope of the bottom of the reservoir or the canal of 19.9° next to the embankment has been found to be relevant. Figure 24 shows the mode of failure if the slope is exceeded.

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 41

Figure 23: View of the circular slip, when the limit state is exceeded.

To assess the maximum possible height of the embankment, a calculation is done to reveal the critical state when base failure is going to occur. A stress of 𝑅𝑅,𝑑𝑑 = 112.4 kN/m2 is found to be relevant.

Table 11: Results of the calculation to find the limited state

If the limit load of 112.4 kN/m2 is divided by the safety factor of 1.4, the resulting pressure is 80.29 kN/m2. Divided by the specific weight 14 kN/m3, a maximum height of the embankment of 5.70 m is obtained. In an iterative process, a maximum slope of the bottom of the reservoir or the canal of 19.9° next to the embankment has been found to be relevant. Figure 24 shows the mode of failure if the slope is exceeded.

35

Figure 24: Maximum slope of 19.9°, with view of a possible slope slip.

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 42

Figure 24: Maximum slope of 19.9°, with view of a possible slope slip. The main results of the geotechnical calculation can be summarized in four bullet points:

The settlement of the projected embankment is 0.56 m. For the projected embankment base failure is not relevant. The maximum height of an embankment is 5.7 m. If a slope of 19.9° next to the embankment is exceeded, slope failure occurs.

Several parameters have been assessed based on the available information. Especially the lack of knowledge concerning the subsoil below parts of the western embankment is a cause of con-cern. With a more detailed soil investigation, which helps to define specific soil parameters, the design can be optimized. But generally the used input parameters and computed values allow a draft design of the constructions. Heavier structure such as sluice gates and pumping stations need to be constructed on deep foundations such a bored piles or displacement piles.

Slope protection The slope of the embankments was proposed to be 1:1.5 and thus is relatively steep. The ad-vantage of this design lies in the reduced required space. Especially due to hydrostatic loads and to a certain extend hydrodynamics loads, the slopes must be protected. The development of waves has been assessed based on predominant wind velocities, the maxi-mum fetch length and the maximum water depth. Applying the approaches of Saville and Young & Verhagen the wave heights is between 0.06 m and 0.14 m with wave periods between 2 and 4 seconds. Generally, various solutions of slope protection are feasible. Besides the conventional technical solutions, such as armour stones, some close-to-nature revetments, such as soil consolidation, wood and fascines, exist and are described below.

The main results of the geotechnical calculation can be summarized in four bullet points:

y The settlement of the projected embankment is 0.56 m.

y For the projected embankment base failure is not relevant.

y The maximum height of an embankment is 5.7 m.

y If a slope of 19.9° next to the embankment is exceeded, slope failure occurs.

Several parameters have been assessed based on the available information. Especially the lack of knowledge concerning the subsoil below parts of the western embankment is a cause of concern. With a more detailed soil investigation, which helps todefinespecificsoilparameters,thedesigncanbeoptimized. But generally the used input parameters and computed values allow a draft design of the constructions.Heavier structure such as sluice gates and pumping stations need to be constructed on deep foundations such a bored piles or displacement piles.

6.1.10 Slope protection

The slope of the embankments was proposed to be 1:1.5 and thus is relatively steep. The advantage of this design lies in the reduced required space. Especially due to hydrostatic loads and to a certain extend hydrodynamics loads, the slopes must be protected.

The development of waves has been assessed based on predominant wind velocities, the maximum fetch length and the maximum water depth. Applying the approaches of Saville and Young & Verhagen the wave heights is between 0.06 m and 0.14 m with wave periods between 2 and 4 seconds.

Generally, various solutions of slope protection are feasible. Besides the conventional technical solutions, such as armour stones, some close-to-nature revetments, such as soil consolidation, wood and fascines, exist and are described below.

36

Armour stones

Full grouting:

y Loosely poured stones

y Cavitiescompletelyfilledwithhydraulicbound,densegrout

y Ability to follow deformation of the underground: limited

Partial grouting:

y Loosely poured stones

y Cavitiespartiallyfilledwithhydraulicbound,densegrout

y Limitedflexibility,determinedbyamountofgrout

Figure 25: Full grouting (left) and partial grouting (right)

Dumped riprap: y Stones dumped on slope (manually or mechanically) y Ability to follow deformation of the underground: high y Simple construction y High material requirement; constant monitoring necessary

Placed riprap: y Stones placed without cavities (manually or mechanically) y Single layer

Gabions: y Rectangularcages,filledwithstones

(daw 2012)

Figure 26: placed riprap (top); dumped riprap (middle); gabions (bottom)

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 43

Armour stones

Full grouting:

Loosely poured stones Cavities completely filled with hydraulic bound, dense grout Ability to follow deformation of the underground: limited

Partial grouting:

Loosely poured stones Cavities partially filled with hydraulic bound, dense grout Limited flexibility, determined by amount of grout

Figure 25: Full grouting (left) and partial grouting (right) Source: Adapted from Baw (2008)

Dumped riprap:

Stones dumped on slope (manually or mechanically) Ability to follow deformation of the underground: high Simple construction High material requirement; constant monitoring necessary

Placed riprap:

Stones placed without cavities (manually or mechanically) Single layer

Gabions:

Rectangular cages, filled with stones (DAW 2012)

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 44

Figure 26: placed riprap (top); dumped riprap (middle); gabions (bottom) Source: Adapted from Baw-Plus (2003)

Soil consolidation

Cohesive soil mixed with binding agent Increased erosion resistance Full embankment made out of consolidated soil / consolidated soil layer on upstream

side of the embankment Possible binding agents: fine lime, lime hydrate, highly hydraulic lime, cement Planting possible

(BAW-PLUS 2003)

Wood

Stands (10 – 25 cm thick) driven into the ground, slope according to embankment slope

Stacking of planks (5 – 8 cm thick) behind the stands

Figure 27: Plank wall Source: Adapted from Bundesanstalt Technisches Hilfswerk (2001)

Fascines

Bundle of sticks, 20 – 60 cm diameter, several meters lengths Held together with wire Can be filled with stones Hold in position by piles / worked into the ground

37

Soil consolidation y Cohesive soil mixed with binding agent y Increased erosion resistance y Full embankment made out of consolidated soil / consolidated soil layer on upstream side of the

embankment y Possiblebindingagents:finelime,limehydrate,highlyhydrauliclime,cement y Planting possible

(baw-plus 2003)

Wood y Stands (10 – 25 cm thick) driven into the ground, slope according to embankment slope y Stacking of planks (5 – 8 cm thick) behind the stands

Figure 27: Plank wall

Fascines

y Bundle of sticks, 20 – 60 cm diameter, several meters lengths y Held together with wire y Canbefilledwithstones y Hold in position by piles / worked into the ground

Figure28:Fascines(left)andfascinesfilledwithstones(right)

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 44

Figure 26: placed riprap (top); dumped riprap (middle); gabions (bottom) Source: Adapted from Baw-Plus (2003)

Soil consolidation

Cohesive soil mixed with binding agent Increased erosion resistance Full embankment made out of consolidated soil / consolidated soil layer on upstream

side of the embankment Possible binding agents: fine lime, lime hydrate, highly hydraulic lime, cement Planting possible

(BAW-PLUS 2003)

Wood

Stands (10 – 25 cm thick) driven into the ground, slope according to embankment slope

Stacking of planks (5 – 8 cm thick) behind the stands

Figure 27: Plank wall Source: Adapted from Bundesanstalt Technisches Hilfswerk (2001)

Fascines

Bundle of sticks, 20 – 60 cm diameter, several meters lengths Held together with wire Can be filled with stones Hold in position by piles / worked into the ground

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6.1.11 Consideration of changing loads (e.g. traffic)

In the initial situation the crests of the eastern embankments and northern embankments are designed as roadsforpredominantmotorbikeandminorcartraffic.Thecrestofthewesternembankmentdesignedformotorbikes.

If the crests of the western embankments are widened, cars will drive on it. Thus, the design load must be adapted. According to Figure 29 the loads resulting from changed dimensions of the embankments can be assumed based on standard design loads for buildings and live loads. For passenger cars a conventional load of 3 kN/m² and a load factor of 1.3 becomes relevant. For a smaller trucks a conventional load of 5 kN/m² andaloadfactorof1.2becomesrelevant.Incomparisontothepermanentloads,thetrafficloadscanbeneglected. However, an appropriate pavement of the road is crucial to avoid damages of the embankment.

Figure 29: Assumed dimensions of various vehicles

6.2 Institutional Feasibility

The institutional feasibility analysis should be considered as a brief assessment of the institutional characteristics and background (both in terms stakeholders and policies – available and required). It further provides a concise assessment on available and required capacities of relevant stakeholders to enable thesetoeffectivelyandsustainablymanagetheproposedwaterreservoir.Ingeneral,theinstitutionalandcapacity assessment is expected to provide a better understanding of formal and informal rules managing thereservoirandinfluencingoperationsanddevelopment.Inaddition,ithelpstoprovideaninitialoverviewof all stakeholders’ interests in the project and their available and required capacities in order to ensure successful implementation.

The below sections will provide i) a stakeholder summary and ii) an assessment of available laws and regulations, followed by analyses on both domestic and international interests and regulations and inter-provincial planning and cooperation. The analysis results in options for additional institutional strengthening in the future.

6.2.1 Stakeholder SummaryIf constructed as planned, Tra Ton-Tri Ton Water Reservoir will be a Hydraulic Works System within the inter-provincialirrigationsystemoftheLongXuyenQuadrangle,managedundertheLXQIrrigationSystemManagement Board1. The board is chaired by the Minister of Agriculture and Rural Development (MARD), vice chaired by the Directorate of Water Resources (DWR) and the Provincial Peoples Committees (PPCs)

1 Decision No. 3334 / QD-BNN-TCCB dated 29 November 2005 of the Minister of Agriculture and Rural Development on the establishmentoftheManagementCounciloftheLongXuyenQuadrangleIrrigationSystem

UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 45

Figure 28: Fascines (left) and fascines filled with stones (right) Source: Bundesanstalt Technisches Hilfswerk (2001)

Consideration of changing loads (e.g. traffic) In the initial situation the crests of the eastern embankments and northern embankments are designed as roads for predominant motorbike and minor car traffic. The crest of the western embankment designed for motorbikes. If the crests of the western embankments are widened, cars will drive on it. Thus, the design load must be adapted. According to Figure 29 the loads resulting from changed dimensions of the embankments can be assumed based on standard design loads for buildings and live loads. For passenger cars a conventional load of 3 kN/m² and a load factor of 1.3 becomes relevant. For a smaller trucks a conventional load of 5 kN/m² and a load factor of 1.2 becomes relevant. In comparison to the permanent loads, the traffic loads can be neglected. However, an appro-priate pavement of the road is crucial to avoid damages of the embankment. .

Figure 29: Assumed dimensions of various vehicles

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of An Giang, Kien Giang and Can Tho Provinces. Further members are relevant provincial and national line departments, such as Departments of Agriculture (DARD), Departments of Planning and Investment (DPI) and Departments of Finance (DOF), non-productive irrigation management companies2 and Southern Water Resources Institutes.

While a dedicated management board or management authority for the proposed reservoir has not yet been established, the An Giang DARD is assumed to have management authority with direct coordination to the LXQIrrigationSystemManagementBoard.InadditiontothecoordinationoftheproposedreservoirtheLXQIrrigation System Management Board is responsible to consider international initiatives, local communities as well as both up- and downstream impacts into management planning3.

Table 12 below provides an overview of all relevant stakeholders (both international organizations/bodies as well as domestic stakeholders, such as public authorities, NGOs, and societal bodies). Stakeholders are classifiedaccordingtotheInternationalFundforAgriculturalDevelopments(IFAD)fieldpractitionersguidefor Institutional and organizational analysis and capacity strengthening (priTchard, m. 2014). According to this IFADGuidestakeholdersareclassifiedas follows:KeyStakeholders,PrimaryStakeholdersandSecondarystakeholderswhichareeithersignificantly,partiallyorindirectlyinvolvedintheprojectimplementation(ibid).

Table 12: Stakeholder Summary

Stakeholder Roles & Responsibilities Stakes/Interests in the reservoir

Key Stakeholders

Provincial Authorities An Giang (DARD, DONRE, PPC)

y Overall management authority of the proposed reservoir

y Responsible for alternative livelihood development for local communities (incl. extension services) and potential compensation payments

y Coordinating role with other affectedprovinces

y Expectation of direct & indirect socio-economic and environmentalbenefitsforAnGiang Province

y Reduction of input costs for irrigation

y Improved productivity of agricultural land surrounding the reservoir

y Improved livelihoods for local people

MARD and Directorate of Water Resources (DWR)

y Chairing & co-chairing the Irrigation council and thus the proposed operations of the reservoir

y Responsible for management, planning and policy development for

y Ensure coordination with needs of neighboring provinces

y considerationofpotentialeffecton other provinces

y Integration of management & operation of the reservoir in national, regional and provincial planning and policy making

2 According to An Giang PPC Decision No. 1702/QD-UBND the former An Giang Irrigation Management Center was transformed into theAnGiangIrrigationCompanywhichuswhollystateownedinthefieldofpublicutility

3 Decision No. 56 / QD-BNN-TL dated 08/01/2006 of the Minister of Agriculture and Rural Development promulgating the Regulations onorganizationandoperationoftheManagementCounciloftheLongXuyenQuadrangleIrrigationSystem

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Stakeholder Roles & Responsibilities Stakes/Interests in the reservoir

Local Communities in Reservoir Area

y Provision of land area for the establishment of the reservoir

y Labor inputs for alternative cultivation options

y Direct changes to livelihoods of local communities within the reservoir

y Impacts on livelihood patterns of communities surrounding the reservoir due to water release

Primary Stakeholders

Provincial Authorities Kien Giang (DARD, PPC)

y External role under the Memorandum of Understanding (MoU) for joint water management between An Giang and Kien Giang

y Potential lack of water due to storage in the reservoir

y Potential agricultural impacts due to water release

Southern Institute of Water Resources Planning (SIWRP)

y Advisory role in planning and development of the reservoir

y Integration of management & operation of the reservoir in national, regional and provincial water resources planning

Upstream Authorities in Cambodia

y Provisionofsufficientvolumesofwatercanbeaffectedthroughrelease/storage of water in upstream dams

y Establishment of the reservoir mightaffectflood&droughtpatterns along the Cambodian border

World Bank ICRSL Project y Identifiedforbothfinancialand technical support for the development and operation of the reservoir

y Consideration of social and environmental safeguards during the establishment and operation of the reservoir

An Giang Irrigation Company

y Operation of alternative income modelsduringfloodseasonwithin the reservoir

Secondary Stakeholders

Viet Nam Disaster Management Authority (VDMA)

y Overseeing water release, especially in situations of high flooding

y Use of the reservoir (water storage and release) to consider potential negative impacts through climate change events

Southern Irrigation Management Board (CPO-10)

y Overseeing irrigation planning and development in the Mekong Delta

y Ensure appropriate irrigation measures and water volumes throughout the Mekong Delta to ensure agricultural productivity

Intl. Union for the Conservation of Nature (IUCN)

y Provision of experiences/lessons learnt on livelihood alternatives and social/environmental management practices

y Consideration of environmentally sound approaches to reservoir management and implementation of livelihood alternatives

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Stakeholder Roles & Responsibilities Stakes/Interests in the reservoir

GIZ y Technical advisory support to An Giang & Kien Giang DARD as well as MARD and its respective line departments

y Integrated management and operation of the reservoir (considering inter-provincial and national interests as well as socio-economic and environmental aspects)

Mekong River Commission (MRC)

y Facilitate regional cooperation in the management of shared resources of the Mekong River Basin.

y Representation of interests of other riparian countries

Downstream Provinces y Potential lack of water due to storage in the reservoir

y Potential impacts due to water release

6.2.2 Laws and Regulations

In this section, major formal and informal policies, laws and relevant social/cultural norms are assessed considering their potential impact on the proposed reservoir. This serves to further explore possible opportunitiestoadjusttheexistinginstitutionalcontext.Table13belowidentifiesmajorformalpolicies,lawsand regulations, social/cultural norms and their potential impacts on the proposed reservoir.4

Table 13: Overview on laws and regulations

Law/Regulation/Norm Major relevant aspects Potential impact

Operational Regulations forLXQ(GIZ&MARD,2017)

y Inter-provincial regulations on operational aspects of water managementintheLXQ

y Regional hydrological monitoring and sharing information.

y + Technical transfer, capacity building on O&M of irrigation system

y Operational rule for Tra Su-Tha La dams and reservoir

y Supporting information for reservoir development and management (land use, water demand, hydraulic modelling, monitoring network, O&M responsibility of organizations)

Mekong Delta Plan (MDP)4

y Future infrastructure development andwaterutilizationinLXQ

y Identifyingfutureflood,salinity, droughtinthearea

y Integrating reservoir into regional irrigation system.

y Outline future operational regulationofreservoirandLXQirrigation system.

4 PrimeMinisterDecision245/QĐ-TTgof12/02/2014“MasterPlanningforsocial-economicdevelopmentintheMekongDeltaregionuntil 2020 with outlook to 2030”;

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Law/Regulation/Norm Major relevant aspects Potential impact

Socio Economic Development Plan (SEDP) An Giang

y Agricultural production targets, guidance on agricultural practices to reach targets

y Plans on social and environmental management in target area

y Operational rules for Tra Su-Tha La dams and reservoir

y Production targets for area within or around the water reservoir

Mekong Delta Water Management Master Plan5

y Water availability the area

y Water sharing in the area

y Improving reservoir water balance andwatersupply 

Master Plan for Development of Rice Production6

y Landuse information

y Strategic rice production & food security

Provincial Climate Change Adaptation Plan

y Identifyingfutureflood,salinity,drought in the area

y Implementation of pilot water supply reservoir in the project area

y Capacity building for water resourcesmanagement,flood/drought risk management

y Changing cropping pattern

y Updating master & sectoral plans, policies.

y Integrating reservoir into regional irrigation system.

y Opportunity for reservoir investment & construction.

y Better reservoir water management & operation

y Changing land use in the reservoir

y Update reservoir project into sectoral development plan

Intention of local communities to increase rice yields

y High rice production, lower rice price, creating opportunity to change paddy land into lotus crop, aquaculture.

y Community support for reservoir development 

6.2.3 Options for institutional strengthening

Based on the above sections the following provides a brief analysis with recommendations concerning international, national and inter-provincial interests and regulations.56

International interests and regulations

The proposed Tra Su-Tri Ton Water Reservoir is relying on upstream water supply without reducing water volume for downstream provinces. As described above, water demands of the reservoir might lead to both i) extendedupstreamfloodingcyclesduetotheclosureofsluicegatesforwaterstoragewithinthereservoir;andii)reducedwaterlevelsaroundtheendofthefloodseasonduetopumpingwhichisrequiredtofillthereservoir to the expected water levels. Both water requirements of the reservoir from upstream Cambodia aswellaspotentialeffectsontheCambodiansideoftheVietnam-Cambodianborderclosetothereservoirrequire close coordination and cooperation between relevant authorities of both sides of the border. While this is possible through direct channels, the inclusion of the Mekong River Commission as a coordinating bodymightbebeneficialtoensuretherequiredcoordinationandpotentialgrievancemechanisms.

5 PrimeMinisterDecision1397/QĐ-TTgof25/09/2012“MekongDeltaIrrigationMasterPlanningintheContextofClimateChangeandSea Level Rise by 2020 and outlook to 2050”;

6 Decision 101/QĐ-BNN-TT of 15/01/2015 of the Ministry of Agriculture & Rural Development (MARD) on the “Master Plan onDevelopment of Rice Production in the Autumn-winter Season in the Mekong delta to 2020 with outlook to 2030”

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National and regional interests and regulations

So far, a lack of integration of and coordination with relevant MARD authorities (most prominently DWR and SIWRP) was observed due to limited knowledge and awareness within MARD of the intended reservoir proposal.

In addition, based on the new Planning Law7 all initiatives are supposed to be in line with higher level laws and regulations (integrated spatial planning, relevant for national & regional plans in this case) and require a thorough Strategic Environmental Assessments (SEA). Based on Table 13 above there are a multitude of laws andregulationsinplace,which,eachindifferentways,haveimpactsormightbeimpactedbytheproposedreservoir. Relevantmodificationswould be required to ensure an integrated planning andmanagementapproachacrossdifferentsectorsandtheirrespectiveplans.

Inter-provincial planning and cooperation

In general, agreement of An Giang and Kien Giang Province on the concept and purpose of the reservoir wasobserved,eventhoughthebenefitsforKienGiangwouldberatherlimitedunderthecurrentproposalofthereservoir.Operationalaspectsaswellasprovincialneeds(suchasensuringsufficientwatersupplyforirrigation) would be addressed through an inter-provincial coordination committee8.

Tofurtherensurethefinancialsustainabilityoftheproposedreservoiranintegrationintotheupcoming5year Socio Economic Development Plans (SEDP) as well as upcoming regional planning exercises such as the Mekong Delta Master Plan would be required. This process would allow for increased coordination as well as domestic budgeting of management and operational costs.

6.3 Environmental Feasibility

6.3.1 Soil contaminants

Generally, arsenic (As) is a ubiquitous element that is found in the crust of the earth and in igneous and sedimentary rocks in a lower concentration as for example in marine sediments. It occurs in air, soil, water, plants,rocks,andanimals.Naturalactivities, likevolcaniceruptionorforestfiresmayreleasearsenic intothe environment (viThanage 2016). The main naturally occurring process releasing arsenic is weathering. As sulfidesconvertarsenicintothemobile,orsoluble,formarsenicacid(As(V)), itcanenterintothearseniccircle as solution in e. g. rain water or as dust (maiTy eT al. 2011). Uptake of arsenic by crops is caused by arsenic in soils (huang eT al. 2006). Beside its natural origin in the earth crust, arsenic is generated by several anthropogenic activities like coal burning, animal manures or irrigation with arsenic-contaminated water (bhaTTacharya eT al. 2007). Lower As contents in the soil occur due to the loss of As by microbial bio methylation processesfromthesoilintotheair.Fromtheairanuptakebyplantsorinfiltrationinthesurroundingoccurs.Some surveys pretend that the potential risk of surface or groundwater contamination is low because As is morehighlyconcentratedinsoilsorinrocks.Factorswhichareaffectingthelevelsofarsenicinsoilsinclude(mandal & suzuki 2002):

y Parent rock

y Organic and inorganic components of the soil

y Redox potential status

In natural water bodies the occurrence of As has received attention in recent decades, because it is found in low concentrations. In several countries, the maximum permissible concentration is 50 µg As/l for drinking water. However, while the World Health Organization (WHO) guidelines suggest standard values for 10 µg

7 Developed by the Ministry of Planning and Investment (MPI) and approved adopted by the National Assembly on 24.11.2017

8 Asregulatedunderthe‘AgreementonjointwatermanagementoftheLongXuyenQuadranglebetweenAnGiangandKienGiangProvinces signed on June 7, 2012’

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As/l (viThanage 2016). The mobility of arsenic in soils and groundwater depends on: pH-values, redox potential, dissolved organic matter, presence of adsorbents like oxides and hydroxides, humid substances, and the percentage of clay minerals (bissen & frimmel 2003). As release processes occur inavarietyofdifferentgeochemicalenvironmentsdepending on the initial position (viThanage 2016). Many people living nearby or in these areas are strongly affected by arsenic groundwater(bhaTTacharya eT al. 1997). In the Mekong Delta the reductive dissolution of arsenic and arsenic bearing iron(Fe)oxidesisoneofthemostsignificanttriggersto release arsenic into the groundwater (bauer & blodau 2006).

In tide-dominated areas, soils are rich in iron sulphides (husson eT al. 2000) which are responsible for pH-values below three. In addition to iron sulphides, iron, ammonium, arsenic, and dissolved organic carbon (DOC) is found in the soils. Iron hydroxides are one of the most common phases associated with aquifer sediments. Desorption mechanisms of As from Iron hydroxide are responsible for the existing high concentrations of mobile Arsenic in groundwater (islam eT al. 2013). For releasing As from soils and sediments, it is important taking into account the competition between As and organic anions at sorption sites within their redox potentials. One of the potential As-sources are fertilizers: phosphate fertilizer is often used for manuring. However, As is absorbed onto phosphate (sTanger eT al. 2005).Duetoincreasingacidification,the water of rivers and canals is suboptimal for using as irrigation water. According to berg eT al. (2006) about 40 % of all groundwater wells in the MD had arsenic levels >100 µg/l. Elevated arsenic levels cause pH-values > 7. In less than ten kilometers distance from the Hau River, arsenic concentrations of 64 µg/l can be found. The average concentrations decreases to 8 µg/l occur if the radius increases (berg eT al. 2006). These high As concentrations are not only found in the groundwater but rather in tube wells for the supply of drinking water. This presents a risk of chronic As poisoning to several million people which consume untreated groundwater for drinking (viThanage 2016 and berg eT al. 2001).

Especially in case of dredging, the dredged material must be handled according to prevailing regulations on handling of hazardous materials. Before being re-used the dredged material must be analysed and only be used according to the results of the analysis.

It is assumed that an unlimited application of the dredges soil is not feasible. It must be ensured that dredging does not mobilize pollutant existing in the lower soil layers.

6.3.2 Soil acidification and soil management

The result of decreasing pH-values in soils over a long period of time is soil acidification. Signs forthis phenomenon are often invisible. Under natural conditions acidificationmayoccurover thousandsof years but areas with high precipitation are mostly affected (deparTmenT of environmenT and resource managemenT 2000). The process affects soil andsubsoil to a similar degree. Truong (2002) pointed out that there are threedifferent typesof soils inthe Mekong Delta:

y Saline soils

y Alluvial soils

y Acid sulphate soils

Dredging of soil was seen very critically from many stakeholders since it will decrease the quality of the soil for agricultural purposes and thus influencethe livelihood. The researched information and data on soil pollutants confirmed this perception.Furthermore, dredging requires the permission of the Prime Minister and complicates the approval procedure. Further, dredging may mobilize pollutants that now are bonded in the subsoil. A transportwiththewaterflowtodownstreamareaswill have negative impacts on the Tra Su forest.

Costs for earth works including loosening, grabbing, transport and dumping are assumed to be around 6 USD per m³. The projected volume of 1 million m³ dredged material will consequently raise costs, that are high compared to the investment costs. Follow-up costs such as the creation and removal of temporary roads, the designation of dumping areas and the recovery of the existing roads and areas will increase the costs for the design alternatives that require dredging. Assuming that the dredged material will be stored temporarily and used completely for construction purposes afterwards, the overall costs will be up to 10 USD per m³ resulting in additional costs of 10 million USD for the dredging. If cleaning and disposal of the dredged

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soil is required, this will further increase the costs.

Assuming that the elevation in the reservoir area is as stated in Table 5, and thus by 0.50 m higher in average than mentioned in the proposal, costs for dredgingwillsignificantly increase–accordingtoafirstssessmentbyfactor2.

6.3.3 Biodiversity

Biodiversity in the Mekong Delta is characterized through its seasonal changes due to direct and indirect monsoonal impacts. These seasonal events lead to regular changes in biological diversity and

habitat availability (COATES ET AL. 2003). Floodplains, such as the proposed Tra Su-Tri Ton reservoir area are a good example for these changes during flood and drought seasons. Generally, the annualspreading of floodwaters is associated with anincrease in aquatic life while drought seasons are representative for increase arthropod diversity. The absence or presence of floods results in differenthabitatsduringdifferenttimesduringoneyearandare of importance to provide breeding grounds for fishbutalsotosupportdecompositionofvegetationwhich in return provides additional nutrients for future rice cultivation (see Figure 30).

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UNIQUE | Feasibility Study Tra Su – Tri Ton Reservoir 55

Figure 30: Seasonal changes in ecology over the flood cycle Source: Coates et al. 2003

Figure30:Seasonalchangesinecologyoverthefloodcycle

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Changestothefloodregimesthroughtheestablishmentofalargescalereservoirwillhaveimpactsontheecosystems which are used to regularly living with and without water, especially within the boundaries of the reservoir.Sucheffectscouldbe:

y Reduction in arthropod diversity due to reduced drought occurrences

y Changesinaquaticdiversity,suchasunder-/overpopulationofspecificfishspecies

y Changes in bird populations, which are nesting in nearby Tra Su Melaleuca forest and partially feed of eitherfishorinsectsinthesurroundingareas.

6.3.4 Tra Su Melaleuca forest

The Tra Su Melaleuca forest covers a total area of 2,800 ha which was planted in 1978. Its major tree species is Melaleuca Cajuputi. In addition Eucalyptus was introduced along the fringes of the forest. Melaleuca are considered a native tree species in An Giang Province and were found throughout the province. Yet in recent decades large parts were converted to rice paddy for agricultural cultivation, resulting in protection and rehabilitationeffortsunderTraSuProtectionForestManagementBoard.

Table 14: Overview on Ecosystem services of wetlands

Ecosystem Service Description Relative magnitude

ProvisioningFood Productionoffish,fruits,grain,honey,etc. HighFresh water Storage and retention of water, provision of

water for irrigationMedium

RegulatingClimate regulation Regulation of greenhouse gases, temperature,

precipitation and other climatic processesMedium

Hydrological regimes Groundwater recharge & discharge, water storage

Medium

Natural hazards Flood control, storm protection MediumCulturalRecreational/Aesthetic Tourism, appreciation of natural features MediumSupportingBiodiversity Habitat for species MediumNutrient cycling Storage, recycling, processing of nutrients HighSoil formation Sediment retention and accumulation of

organic matterMedium

Source :adaptedfromRussietal.2013.

Tra Su Melaleuca forest is considered a bird sanctuary and of high conservation value, since it is home to an abundanceofbirds,Amphibiaandfreshwaterfish,indicatingadiverseandbalancedwetlandecosystem.TheTra Su Melaleuca forest is providing important ecosystem services (see Table 14 above), which can be valued at up to 44.000 $USD/ha per year.

Initially itwasproposedthattheforestwillbe integrated inthereservoirandfloodedalongwiththerestof the proposed area. This would result in an increase of its natural maximum water levels of 3.5m to 4.5m as proposed for the reservoir at hand. After consultations with local authorities it was understood that the Melaleuca forest ought to be excluded from the proposed reservoir. As it otherwise might have several negativeeffects:

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y Loss of biodiversity values within the forest

y Disruption of the wetland ecosystem due do irregularflooding

y Negative effects on downstream agricultureas soils, and thus water, from within the reservoir are very acidic and might reduce rice productivity

y Introduction of invasive species into the melaleuca forest from outside areas or through aquaculture practices in other parts of the reservoir

y Loss of its cultural and touristic value due to deterioration of the wetland forest ecosystem

Further to the above outlined potential negative effects,othernegativeresultscouldgenerallyresultin a decrease of ecosystem service provision and quality of all serveries as described in Table 14 above.

The establishment of the proposed water reservoir wouldhavedifferentimpactsintheTraSuMelaleucaforest. Impacts would arise for both cases: i) inclusion of the forest into the reservoir; or ii) exclusion of the reservoir but extension of the reservoir south of the forest. The below section gives a short summary of potential impacts, yet further studies are required in order to quantify these in more detail. Such impacts includeeffectsoneco-tourismactivities inside theprotection forest, damages to the ecosystem and changes in operational costs.

Effectsoneco-tourism

Including the Melaleuca forest in the proposed reservoir increases the threat of ecosystem degradation which in parallel would result in a loss in its aesthetic and recreations value. This could result in a reduction of tourists, which mostly visit the site in order to appreciate the wetlands natural features. Considering that the ecotourism site is set up in a waythatbenefitslocalcommunitiesthiscouldresultin reduced income for up to 400 households which directlyor indirectlybenefit fromtourismactivitiesin the area.

Potential damages to the ecosystem

As laid out in previous sections, the inclusion of the forest into the reservoir could result in ecosystem degradationasfloodingregimeswouldchangeand

potentially result in damages for both flora andfauna. With an estimated maximum ecosystem value of 44.000 $USD/ha, a high amount of indirect damages can be expected from the inclusion. While the exact financial values could not be estimateddamages would include a reduction of biodiversity, reduced climate regulation through the wetland area, reduced food sources and direct/indirect livelihood opportunities from the forest.

Changes in operational costs

In both cases, inclusion of the forest and exclusion of the forest the flood control operations ofopening and closing sluice gates would need to be harmonized to either ensure same water levels throughout the reservoir, or exclude the forest from the reservoir and thus maintain water levels within the Melaleuca forest or ensure sufficient watersupply. Such harmonization required increased coordination and potentially increased labour inputs.Thesewouldneedtobequantifiedfurther.

Considering these potential negative impacts, it is not recommended to include the Tra Su Melaleuca Forest in the reservoir. Alternatively, it could be considered to extend the reservoir southwards, which would result in the Melaleuca forest being surrounded by the reservoir. Considering the differences in maximum water levels an increaseof dykes around the Melaleuca forest would be of utmost importance to ensure no interference of the reservoirs higher water levels with the Melaleuca wetland ecosystems. Hence, operation of water management within the reservoir and the Melaleuca forest should be well coordinated and in line to ensure that water regimes within the reservoir are preserved even though the surrounding environment changes. Alternatively the location of the reservoir could be changed as a whole in order tonotaffecttheMelaleucaForest.

The increased water storage capacities in the surrounding area can also be beneficial for themelaleuca forest, as under current conditions it is required to pump in additional water resources (of up to 40.000.000m³/year) into the forest to ensure sufficient water provision also during dry-seasons. Hence, these volumes could in the future be provided through the proposed Tra Su-Tri Ton water reservoir.

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6.4 Socio-economic Feasibility

Consideringthefindingsoftheenvironmentalassessment,itseemsreasonabletoassumethatAlternative1 to 3, which requires dredging and the flooding of the Melaleuca forest would not pass a social andenvironmental risk assessment. The following socio-economic assessment thus concentrates on Option 4, which explicitly exclude the Melaleuca forest and does not require severe dredging.

Considering the average land size per household in An Giang of 0.89 ha, it can be assumed that around 2.444householdsaredirectlyaffectedbythereservoirconstruction,whereasaround20.565householdswouldbenefitfromthereservoir(e.g.intermsofavoidedlossofagriculturalproductionduetodroughtsandreduction of pumping costs). Table 15 illustrates the scale of the planned reservoir.

Table 15: Scale of reservoir (Option 4)

Given the technically required investments, total construction costs (6 years) sum up to approximately 21 m US$ (see Table 16 ). Construction unit costs are based on data provided by MARD/DARD. Besides construction costs, total annual maintenance and management costs of 292.450 US$ are expected to occur. For that, maintenance costs of 3% of the total construction costs were assumed. Furthermore, annual pumping costs, which are based on consultant’s experience from comparable assignments, have been considered. The construction of the new embankments further requires resettlements. Based on cost norms from previous projects/programs, total compensation costs for resettlement of 300,000 US$ were assumed.

Table 16: Construction costs

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production due to droughts and reduction of pumping costs). Table 15 illustrates the scale of the planned reservoir.

Table 15: Scale of reservoir (Option 4)

Given the technically required investments, total construction costs (6 years) sum up to approx-imately 21 m US$ (see Table 16 ). Construction unit costs are based on data provided by MARD/DARD. Besides construction costs, total annual maintenance and management costs of 292.450 US$ are expected to occur. For that, maintenance costs of 3% of the total construction costs were assumed. Furthermore, annual pumping costs, which are based on consultant’s ex‐perience from comparable assignments, have been considered. The construction of the new embankments further requires resettlements. Based on cost norms from previous projects/pro-grams, total compensation costs for resettlement of 300,000 US$ were assumed.

Table 16: Construction costs

Land use maps have shown that both the target area for the construction of the proposed res-ervoir and the benefitting area is dominated by double rice cropping. The first crop (the Winter- spring crop) is from December to late February, the second crop (the summer-autumn crop)

Key variable Unit Value Total reservoir area ha 2,175 Total embarkment length km 21 Total volume of reservoir m3 83,737,000 Total area benefitting ha 18,303 Total hh reservoir number 2,444 Total hh benefitting number 20,565

Activity Key variables Unit ValueA Length of heightehning of embarkments m 3,700.00

Costs of heightening of embarkments US$/m 65.00 B Number of pumps number 6.00

Costs of pumps US$/number 420,000.00 C Length of embarkments m 5,000.00

Cost of new embarkment US$/m 250.00 D Length of revetments m 8,700.00

Costs of revetments US$/m 350.00 E Length of crest/road cover m 8,700.00

Cost of crest/road cover US$/m 25.00 F Sluice gates number 4.00

Costs of sluice gates US$/number 3,307,500.00 Total construction costs (6 years) US$ 20,803,000

A-B-C-D-E-F Total annual maintenance costs US$/year 230,450Total annual pumping costs US$/year 62,000 Total annual maintenance/management costs US$/year 292,450Compensation for resettlements (new embankments) US$ 300,000Total construction/maintenance/management cost (6 years) US$ 21,494,350

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production due to droughts and reduction of pumping costs). Table 15 illustrates the scale of the planned reservoir.

Table 15: Scale of reservoir (Option 4)

Given the technically required investments, total construction costs (6 years) sum up to approx-imately 21 m US$ (see Table 16 ). Construction unit costs are based on data provided by MARD/DARD. Besides construction costs, total annual maintenance and management costs of 292.450 US$ are expected to occur. For that, maintenance costs of 3% of the total construction costs were assumed. Furthermore, annual pumping costs, which are based on consultant’s ex‐perience from comparable assignments, have been considered. The construction of the new embankments further requires resettlements. Based on cost norms from previous projects/pro-grams, total compensation costs for resettlement of 300,000 US$ were assumed.

Table 16: Construction costs

Land use maps have shown that both the target area for the construction of the proposed res-ervoir and the benefitting area is dominated by double rice cropping. The first crop (the Winter- spring crop) is from December to late February, the second crop (the summer-autumn crop)

Key variable Unit Value Total reservoir area ha 2,175 Total embarkment length km 21 Total volume of reservoir m3 83,737,000 Total area benefitting ha 18,303 Total hh reservoir number 2,444 Total hh benefitting number 20,565

Activity Key variables Unit ValueA Length of heightehning of embarkments m 3,700.00

Costs of heightening of embarkments US$/m 65.00 B Number of pumps number 6.00

Costs of pumps US$/number 420,000.00 C Length of embarkments m 5,000.00

Cost of new embarkment US$/m 250.00 D Length of revetments m 8,700.00

Costs of revetments US$/m 350.00 E Length of crest/road cover m 8,700.00

Cost of crest/road cover US$/m 25.00 F Sluice gates number 4.00

Costs of sluice gates US$/number 3,307,500.00 Total construction costs (6 years) US$ 20,803,000

A-B-C-D-E-F Total annual maintenance costs US$/year 230,450Total annual pumping costs US$/year 62,000 Total annual maintenance/management costs US$/year 292,450Compensation for resettlements (new embankments) US$ 300,000Total construction/maintenance/management cost (6 years) US$ 21,494,350

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Land use maps have shown that both the target area for the construction of the proposed reservoir and thebenefittingareaisdominatedbydoublericecropping.Thefirstcrop(theWinter-springcrop)isfromDecember to late February, the second crop (the summer-autumn crop) starts in early April and is harvested inJuly(seeTable17).Plotsaresurroundedbylowembankmentsofaround2meters,whichallowfloodingafter the harvest of the second crop. At the end of November, when water levels recede, water is pumped out of the plots to sow winter-spring crop. During the summer-autumn crop, water is pumped in at an interval of2weeks.Thesesystemstakeadvantageofthefertilesedimentsthatresultsfromflooding,reducingtheapplication of fertilizers and pesticides.

Double rice cropping system requires water levels, ranging between 0.0 and 0.15 m. As the reservoir would be floodedfromOctobertoJanuarywithamaximumwaterlevelof4.5mandaminimumwaterlevelof1.5minthe dry season, double rice cropping would not be longer suitable/feasible within in the reservoir area.

Table 17: Seasonal calendar of double rice cropping system

Month 1 2 3 4 5 6 7 8 9 10 11 12Winter-Spring

Summer-Autumn

Flood

Theforgoneprofitsofaffectedfarmershavebeencalculatedbasedoncropbudgets,providedbyGIZat2014prices.Table18showsthebudgetfordoublericecroppingsystemwithatotalprofitof1.005US$/ha.Assuminganaveragelandsizeof0.89ha,farminghouseholdsfaceannualforgoneprofitsof890US$ifnoalternative livelihoods models are implemented on the area within the reservoir. Given a total reservoir area of2.175hatotalannualforgoneprofitsof2.185.747US$occurannually.

Table 18: Agricultural budget for double rice cropping system

Cost norms (US$/ha) Winter-Spring Summer-AutumnSeedlings 79 64Preparation of land 66 81Fertiliser 219 175Pesticide 202 180Irrigation/Pumping 65 86Labour 101 94Harvest 139 150Depreciation fixed assets 27 12Interest 16 0Others 14 0Total costs (US$/ha) 927 842Yields (kg/ha) 7.000 5.400Farm gate price (US$/kg) 0,22 0,22Total revenue (US$/ha) 1.566 1.208Totalprofit(US$/ha) 639 366

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Farmers’ acceptance of the reservoir will largely depend on the profitability of alternative flood-basedlivelihoodsystems.Inthefollowingalternativeflood-basedlivelihoodmodelsarethusproposed,consideringthe technical design of the reservoir. Based on consultations with DARD/MARD and IUCN and desk study, the following farming systems will be further discussed and economically assessed:

y Floating vegetable gardens

y Lotus-fishfarming

Floating vegetable gardens

Floating gardening is a form of hydroponics or soil-less culture, also known as vasoman chash, baira, or dhap in Bangladesh, and kaing in Mynamar. Historically, aquatic plants such as water hyacinth (Eichhornia crassipes), algae, straw,herbs, andwaterwort areused to construct thick floatingplatformsonwhich seedlingsareraised and vegetables and other crops cultivated in the monsoon season. This type of agriculture technology has been used to grow leafy vegetables (e.g., lettuce), tomatoes, turmeric, okra, cucumbers, chilies, melons, flowers,pumpkins,andseveraltypesofgourd,beetroot,papaya,andcauliflower,amongothercrops(Islamand Atkins 2007).

Figure 31: Floating gardens in Bangladesh (Source: Rahman)

Floating gardens are seen today as a strategy to diversify production in common property wetlands and to copewithclimatechangeeffectswhereverfloodingmakelandunavailableforagricultureforlongperiodsof time (Parvej, 2007). Since 1999, IUCN Bangladesh is facilitating the expansion of floating gardens, asan alternative flood- based livelihood model for marginalized communities (Sustainable EnvironmentManagement Programme (SEMP), SHOUHARDO). Recent design improvements include beds constructed out of materials that do not rely on organic material as their base (Islam and Atkins 2007).

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Potentialstrengthsofthesefloatinggardensinclude:

y Low-technology production system (associated low input costs) with low up-front investments (Pantanella et al. 2011)9

y Relativelyhighperhaprofitability

y Shortening of production cycle of crops, allowing regular income

y Furtherincomediversificationpossiblethroughintegrationwithfishaquaculture

y Used rafts can be converted into organic residue that fertilizes other crops in areas where inundation is only seasonal (Irfanullah 2013)

y Improvement of water quality and reduction of water disease outbreaks through water hyacinth

Potential barriers may include:

y Labor intensive technology compared with rice production

y Low availability of an adequate mix of plant material for bed creation (UNFCCC 2006); this barrier can be overcome with the implementation of other bed designs.

y Highly vulnerable to salinity intrusion and precipitation variability

y Weak market access (weak linkages with markets and relevant market stakeholders, high food quality standards, high post-harvest losses)

y Technology not yet applied in Mekong region.

Intermsoffloatingvegetablegardens,empiricalevidencefromVietnamislacking,includingcropbudgets.Floating garden trials conducted in Thailand indicate similar yield and productivity levels in comparison to high-inputagricultureon“regular”farmland.Examplesincludelettuceandcabbage(IslamandAtkins2007;Pantanella et al. 2011). Hence, it seems to be reasonable to use budgets from high-input agriculture on “regular”farmland.

In An Giang, upland crops such as cassava, chili, pumpkin, eggplant, leek, cucumber, maize or taro are commonly rotated with rice crops (Nguyen, 2015). Assuming two seasons and an equal distribution of area assigned tochiliandpumpkinproduction, totalprofitsof3,855.33US$perhabedandyearareapplied(Nguyen2015).Ithastobeconsideredthatthesenumbersrefertoeffectivecultivationononeentireha.Thetotalrequiredwaterareaforonehaofbedsneedstosignificantlylargertoaccountforwaterchannelsfortransportation etc. Furthermore this assumption does not yet consider the potential to combine this form of agriculturewithaquaculturepractices,suchasfishraising.

Lotus-fishfarming

Duetoitshighfloodretentioncapacity, lotusproductionoftenintegratedwithaquacultureisincreasinglypromotedasanalternativeflood-basedlivelihoodmodel.LotusplantsintheMekongDeltausuallygrowanddevelopduringthefloods,sotheycanspreadoverlakesandotherbodiesofstandingwater.Allpartsoftheplant,suchasflowers,leaves,seedsandrootsareharvested.Forexample,flowersareusedfordecoration,roots and seeds, as ingredients for food or medicine. Furthermore, due to their high aesthetic value during floweringseasonsomelotusfieldsintheMekongDeltaarepopularecotourismdestinations.Lotusspeciescurrently available in Mekong Delta require water levels between 5 and 150 cm. According to IUCN, other species, currently cultivated in Bangladesh accept water levels up to 4-5 m. It needs to be further assessed whetherrapidincreasingwaterlevelsduetosluicegatesdischargemaycausedifficultiesforlotusproduction.EvidencefromVietnamshowthatLotus-fishproductionyieldanaverageprofitof130MioVND/ha(Nietal.2016).

9 However, according to one study, cultivation costs have risen recently (IUCN et al. 2009). Islam and Atkins (2007, 132) note that a “60-metrefloatingwaterhyacinthraftcostsaboutTk1,500[equivalentto$23]”tomakeandthataboutsevenfloatingraftsarebuiltforeachhectareofwetland.Fromthis,thestudyinfersaprofitof$851perhectarefromfloatingagricultureinoneseason(IslamandAtkins 2007).

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Figure32:Lotusfishfarm

Potentialstrengths lotus-fishfarmingasanalternativelivelihoodmodelinclude:

y Highprofitabilitycomparedwithdoublericecropping

y Low-input agriculture, low upfront investments

y Low disease and pest pressure

y High aesthetic value, relevant for ecotourism

y High demand, reported by processing companies in Dong Thap province.

Potential barriers include:

y High risk of perishability (high post harvest losses)

y High price volatility due to market power of traders and processing companies10

y Labour intensive, requiring daily picking

y High sensitivity to changing water levels and salinity intrusion

The economic impacts of the transformation from intensive double rice cropping to floating vegetablegardens and lotus production are analyzed in section 6.5 below. However, this transformation also requires the implementation of livelihood-related measures at project scale. As proposed in previous and comparable assignments, theadoptionof thealternative livelihoodmodels is fosteredby thesamefivekeyactivities:(i) implementation of clusters/cooperatives; (ii) establishment of demonstration sites; (iii) establishment/strengthening of extension system; (iv) implementation of water quality monitoring facilities and storage facilities;(iv)promotionofcontractfarming.Theseactivitiesareinlinewiththelargefield(canh dong mau lon) program of the Vietnamese Government, encouraging farmers to organize as cooperatives and to establish long-term relationships with companies through contracts. These contracts would cover the supply of inputs,

10 Price for lotus seeds ranges between 4.000- 14.000 VND/kg

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provision of extension advice by company agents, and the purchase of farmers’ produce at agreed prices. The program aims at facilitating productivity increases and reduce transaction costs, particularly for smallholders (Smith, 2013).

Scaling of proposed alternatives

The actual scale of implementing alternative livelihood options would needed to be assessed in detail during the planning and construction phase. The below feasibility, assessment in Section 6.5 considers an area of around1000hatobecoveredbyalternativelivelihoodoptionswhiletakingintoaccountthatthefirsttwo(ofsix) years would be required to set farming systems up while providing relevant extension services11:

Table 19: Scaling overview alternative livelihoods (six-year scenario)

Models Year 1 Year 2 Year 3 Year 4 Year 5 Year 6

Total lotus production area ha - - 800.00 800.00 800.00 800.00

Totalfloatinggardenarea ha - - 200.00 200.00 200.00 200.00

Basedoninterviewsandotherimplementationexperiencesthefollowingcashflows(gainsafterdeductionofcosts) were assumed for both models. As mentioned above, the below assumptions should be used carefully and might need further in-depth assessment, as the number of comparable examples is extremely limited:

Table20:Overviewofperhacashflowsforlivelihoodalternatives

Livelihood model Lotus production Floating garden

Cashflow/ha(USD) 5,702.50 3,855.33

Considering the above-proposed 6-year implementation of livelihood models on a total area of 1000ha, this wouldresultinthebelowpresentedtotalcashflows:

Table21:Totalcashflowsoflivelihoodalternatives

Models Year 1 Year 2 Year 3 Year 4 Year 5 Year 6

Lotus farming USD - - 4,562,003 4,562,003 4,562,003 4,562,003

Floating garden USD - - 771,066 771,066 771,066 771,066

11Thisassumptiondoesnottakefishcage-farmingintoaccountasnoreliablefinancialmodelswereavailableatthattime

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6.5 Economic Feasibility

In the following, the economic viability of structural water management and livelihood-related measures identifiedaboveisanalyzed.TheoverallprofitabilityoftheproposedprojectisindicatedbytheNetPresentValue (NPV) and the Internal Rate of Return (IRR). The analysis is based on a dynamic with and without project comparison. Further, a time period of 30 years and a discount rate of 10% were assumed. As depicted above, in the project scenario, design alternative 4 has been considered.

Themaineconomicbenefitsgeneratedbytheprojectwouldinclude:

y Avoided losses in agricultural production due to drought events and reduction of pumping costs in agricultural sector outside the reservoir.

y Increasedperhaprofitabilitycompared todoublericecropping through theadoptionofalternativeflood-based livelihoodmodels (20% floating gardens, 80% lotus production) within the area of thereservoir.

y Enhanced resilience of natural ecosystems and livelihood systems through the adoption of alternative livelihood systems.

y Improved social stability and overall well-being through reduced risk to natural hazards.

Thedirectbenefitsofthelattertwo(enhancedresilience,andsocialstabilityandwell-being)havenotbeenquantifiedaspartoftheeconomicanalysisgiventhechallengesconcerningtheexactquantification.

To quantify the damages due to drought events, data provided by SIWRP on the drought event in the year 2015/16 are used. Damages are calculated based on the intensity and frequency of drought events. In both the without project and with project scenario the frequency of the 2015/16 drought event of 50 years was applied. Based on the hydrological sketch, the proposed investments induce a reduction in the intensity of damages of 100% for an area of 18.000 ha. Furthermore, the proposed reservoir aims to reduce the pumping costs in the agricultural sector. In both the without and with project scenario, an increase in the annual pumping costs of 10% over 30 years has been considered. Based on hydrological modelling it is reasonable to assume that the pumping costs faced by farmers can be reduced by 50% through the proposed investment.

Aimingatcalculatingtheincrementalbenefitsinducedbythetransformationfromdoublericecroppingtoalternativeflood-basedlivelihoodmodels,one-haagriculturalcashflowmodelsweredeveloped.Assumptionsof agricultural budgets presented above were applied.

Concerning water management all measures listed in Table 16 have been included in the analysis. Due to technical and construction capacity constraints, up-scaling of measures was assumed to be distributed over an entire project length of 6 years. The cost norms for the above presented livelihood-related measures are based on cost norms, provided by World Bank at 2014 prices. Again, an implementation period of the activities and investments of 6 years is assumed.

Afirstassessmenthasshownthat theprofitabilityof theproposed investments ishighlysensitive to thescaling assumptions of the alternative livelihood models. A total reservoir area assigned to alternative agricultural production of only 500 ha yields an IRR of -3%. If the reservoir area would be completely used for agricultural production, an IRR of 34% can be achieved.

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Figure 33: Sensitivity of IRR dependent on scaling of reservoir area assigned to agricultural production.

The feasible scale depends on a number of factors, which would be crucial to understand before any investment decision is made:

y Theeffectofanincrementalproductionoflotus,fishandvegetablesonoutputandinputprices.

y Structure of input markets

y Labor requirements of alternative livelihood models and availability

y Farmer’s acceptance of alternative livelihood models

y Effectsofagriculturalproductiononwateravailabilityandquality

Assuming that 1000 ha of the reservoir could be assigned to alternative agricultural production, the proposed investments would yield an Internal Rate of Return of (IRR) of 15 % and a Net Present Value (NPV) of US$ 9.226 million(ata10%discountrate).Theprojectwouldthereforebeprofitablefromaneconomicperspective.

Table 22: Summary of results from economic analysis

COST/BENEFIT ITEM VALUE

Total project costs (US$) (6 years) 29.212 Mio

Totalprojectbenefits(US$)(6years) 22.559 Mio

Netfinancialbenefits(US$)(6years) -6 Mio

IRR (30 years) 15%

NPV (30 years) 9.226 Mio.

-5

0

5

10

15

20

25

30

35

40

0 500 1000 1500 2000 2500

IRR

(30

year

s)

Total agricultural land (ha)

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However, sensitivity analyses indicate that the IRR reacts on changing climate change projections. Above it has been assumed that the proposed investments would reduce 50 years-drought damages by 100 % on an agricultural production area of 18.000 ha and pumping costs by 50% on the same area in non-drought event years.

Figure 34 shows the IRR dependent on the assumed frequency of droughts, keeping the other assumptions constant.

Figure 34: Sensitivity of IRR dependent on frequency of drought event

Theresultsoftheeconomicanalysisrevealthattheeconomicprofitabilityofplannedreservoirisquestionableat this point. Only under optimistic scaling assumptions, the project would be profitable. Therefore, theeconomics of the project should be carefully considered as part of the further preparation process. The results indicate already that the selection of the alternative livelihood models and the implementation will be keyifprofitabilityoftheinterventionsisoneobjective.

6.6 Environmental and social safeguards

The consideration of Social and Environmental Safeguards is an important aspect in order to identify and mitigate potential harm to local people and the environment in the process of development and establishment of investment projects such as the Tra Su-Tri Ton water reservoir. During the design phase, safeguards should help to identify and assess potential social or environmental impacts associated with the intervention. Major safeguards risks relevant for the reservoir include:

y Pollution

As mentioned in section 6.3.2 dredging to deepen the water reservoir might potentially release pollutants fromsub-soillayers,whichinreturnmighthavenegativeeffectsonagriculturalproductivityoncereleasedwith water for irrigation purposes. Furthermore, including the Tra Su Melaleuca forest into the water reservoir might also result in releasing acidic pollutants, which have build-up in, and are natural to, the Melaleuca forest.

y Resettlement, Livelihoods and Compensation mechanisms

While there are no communities living directly within the reservoir area, resettlement is not an issue there. Yet settlementsarefounddirectlysurroundingthereservoir,thesecouldbeaffectedthroughtheconstruction

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49

IRR

(30

year

s)

Frequency of drought event

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of additional embankments. In addition, local communities are relying on the agricultural area for their livelihoods.Duetotheassumedfloodingwithinthereservoircommunitiesmightsufferfromlossoflandandthe current agricultural practices might not be feasible for this area anymore.

y Biodiversity

As described in Sections 6.3.3 and 6.3.4, the establishment and operation of the reservoir can have direct impactsonaquaticbiodiversityinrivers,channelsandthereservoirareaitselfduetochangesinthefloodregime as well as threats of degradation for the Tra Su Melaleuca forest.

y Community health and safety

Dyke failure and subsequent flooding of surrounding areas poses a major threat to community safetyand in addition might destroy agricultural areas. In addition, having a large unobstructed and unprotected waterbody might increase threats of drowning, especially for children

y Additional safeguards aspects to consider include:

- Current lack of an Environmental Impact Assessment (EIA)

- Work safety

- Consideration of ethnic minorities

- Neutrality stakeholder engagement process

Duringpotential implementationoftheproject,theidentifiedsafeguardsrisksshouldthenhelptoderivemeasures manage and mitigate risks while enhancing potential positive impacts12. Since the revision of the new Planning Law from the Ministry of Planning and Investment (MPI – adopted 24.11.2017) assessments of social and environmental impacts of investment projects are required in the form of Strategic Environmental Assessments(SEA)orEnvironmentalImpactAssessments(EIA).Theabove-identifiedriskswerethenappliedto the World Banks Environmental and Social Standards (ESS13) in order to structure them and propose potential mitigation options.

12 Based on Wold Bank Environmental and Social framework (available online under: http://documents.worldbank.org/curated/en/383011492423734099/pdf/114278-WP-REVISED-PUBLIC-Environmental-and-Social-Framework-Dec18-2017.pdf) and FAO Environmental and Social Safeguards Standards (available online under the Investment Learning Platform: http://www.fao.org/investment-learning-platform/themes-and-tasks/environmental-social-safeguards/en/)

13ESS7-9(indigenouspeople,culturalheritageandfinancialintermediaries)havebeenexcludedastheyareconsiderednotapplicablein the case of Tra Su Tri Ton water reservoir

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Table 23: Environmental and Social Safeguards assessment (based on World Bank Environmental Social Standards)

Standard Relevant objectives(acc. to WB-ESS)

Identifiedsafeguardsrisks Mitigation option for reservoir

ESS1: Assessment and Management of Environmental and Social Risks and Impacts

y Infrastructure projects demand detailed impact assessments both under international and national requirements, in order to:

- Anticipate and avoid risks and impacts;

- Minimize or avoid risks and impacts

- compensate for or offsetifrisks/impactsremain

y Up to now, no EIA has been carried out in the context of the reservoir proposal. Being required under both national law and from potential international donors the EIA would be required to also assess other relevant safeguards risks

y Carry out detailed impact assessment (considering other ESS) according to national requirements and requirements of potential other lenders once finalprojectproposalisdeveloped

ESS2: Labor and Working Conditions

y Promote safety and health at work.

y Prevent use of forced labor (incl. child labor)

y Promote the fair treatment of all workers project workers.

y Threat of physical harm from on-site works during construction phase

y Address work safety concerns in construction contracts and working requirements

y Enforce international requirements and national labor law

y Offeroptionsforworkersto raise concerns

ESS3: Resource Efficiencyand Pollution Prevention and Management

y To promote the sustainable use of resources,

y To avoid or minimize adverse impacts on human health and the environment from pollution

y To avoid or minimize generation waste.

y To minimize and manage the risks and impacts of pesticide use

y Release of pollutants from subsoil layers due to dredging of acidic pollutant buildup from Tra Su Melaleuca forest might threaten agricultural productivity in surrounding area and pose health concerns for neighboring communities

y Identify use/safe disposal sites of earthworks produces from dredging

y Promote & develop pesticide free cultivation options within and around the reservoir

y Ensure regular drainage to reduce pollutant buildup within the reservoir

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Standard Relevant objectives(acc. to WB-ESS)

Identifiedsafeguardsrisks Mitigation option for reservoir

ESS4: Community Health and Safety

y To anticipate and avoid adverse impacts on health and safety of communities

y Tohaveinplaceeffectivemeasures to address emergency events.

y Threat of drowning in the reservoir for children

y Threatoffloodingduetodyke failure and resulting loss of homes and livelihoods

y Provide safety guidance and awareness raising events to reduce threats from drowning in the reservoir

y Have emergency measures prepared in case of dyke failure and resulting flashfloods

y Ensure implementation of quality standards for dyke construction to reduce risks of breakage

ESS5: Land Acquisition, Restrictions on Land Use and Involuntary Resettlement

y To avoid or minimize involuntary resettlement or forced evictions

y To mitigate adverse social and economic impacts by providing timely compensation for potential losses

y To improve living conditions of poor or vulnerable people

y Loss of land and/or reduction of agricultural productivity for communities owning land within the reservoir

y Potential resettlement due to building of additional embankments

y Low impact spatial planning considering local communities also to include assessment of impacts on settlement due to additional embankments

y Resettlement should be avoided as far as possible. Ifnotpossiblesufficientcompensation should be provided

y Potential compensation mechanisms have already been discussed with local communities

y Ensure implementation of compensation mechanisms and provide additional alternative livelihood opportunities

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Standard Relevant objectives(acc. to WB-ESS)

Identifiedsafeguardsrisks Mitigation option for reservoir

ESS6: Biodiversity Conservation and Sustainable Management of Living Natural Resources

y To protect and conserve biodiversity and habitats.

y To promote the sustainable management of living natural resources.

y To support livelihoods of local communities,

y Impacts on habitats and aquatic life in reservoir duetochangeoffloodingpatterns

y Threat of environmental degradation within Melaleuca forest

y Exclusion of Tra Su Melaleuca Forest from the project design

y Precautionary measures and integrated/coordinated water management to not affectecosystemswithinTra Su Melaleuca forest

y Develop alternative livelihood models which consider low environmental impacts or improvement of biodiversity

ESS10: Stakeholder Engagement and Information Disclosure

y To establish a systematic approach to stakeholder engagement

y To assess the level of stakeholder interest and support for the project and to enable stakeholders’ views to be taken into account

y To ensure that appropriate project information on environmental and social risks and impacts is disclosed to stakeholders

y Toprovideproject-affectedparties with accessible means to raise issues and grievances

y In its current form there is no in-depth knowledge on stakeholder consultation processes, how these are organized or what information on the reservoir is available to the local communities in the area

y Continue already ongoing stakeholder engagement and operationalize approach throughout reservoir operation

y Consideration of relevant aspectssuchaseffectsonethnic minorities (K’hmer) and gender aspects

y Development of a grievance mechanism in the form of regular meetings between local communities and relevant authorities

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6.7 Capacity development needs

In thissectionkeystakeholders,as identifiedabove,willbeassessed in termsof theircapacitystrengthsandweaknessesconcerningtheirrespectiveroleswhichtheyareexpectedtofulfilwithintheoperationandmanagement of the reservoir. In a further step, expected outcomes and the capacity needs to reach these willbeanalyzedconcerningspecificstakeholders.

Table 18 below provides a brief SWOT Analysis for each key stakeholder, followed by a proposal on capacity developmentmeasuresandidentificationoflearningandinnovationoptionsaccordingtoCapacityWORKS(GIZ, 2015). The analysis is based on expert interviews and available literature.

Table 24: Capacity SWOT analysis on central/regional as well as prvincial level

Stakeholder Strength Weakness Opportunity Threat

National/Central Level

y Relevant legal framework in place

y Experiences and authority in policy making, management and planning

y Lack of coordination and joint decision making/integrated planning between national and provincial level

y Lack of implementation of legal provisions

y National level integration in provincial/regional participation mechanisms

y Potentially large amount of public andODAfinanceavailable to enhance post-investment management

y High level of support from outside sources (ODA)

y Strong commitment to improve integrated planning

y Regional planning exercise as a chance to improve coordination

y Integrated/participatory management approaches become redundant due to lack of implementation of legal provisions

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Stakeholder Strength Weakness Opportunity Threat

Provincial Level14

y Understanding of intended impacts

y Experiences in implementing extension services

y Direct planning and managing authority

y Direct incomes from irrigation work (at least VND 50bn/year) and available human capacities

y So far, limited coordination with neighboring provinces on the operation of the reservoir

y Lack of funding and human capacities at management and technical level

y Limited availability and knowledge on potential alternative livelihood options for the reservoir

y High level of support from outside sources (ODA) and strong national level commitment to increase integrated planning

y Inter provincial approaches (proposed reservoir or regional planning exercise) as chance to enhance inter-provincial coordination

y Available lessons learnt and support from ODA for livelihood development

y Reduction of available funding due to lack of outcomes/accountability and high opportunity costs

Cross-cutting aspects

y Available legal framework

y Limited availability offinancialdatato improve management/funding allocation

y Lack of policy implementation and coordination

y Transition towards more climate resilient livelihood options

y Funding availability to improve climate resilience aspects in the Mekong Delta

jf;adlskfjal14

14 The focus of this analysis will be on the An Giang DARD as potential management & implementing authority of the proposed reservoir

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6.7.1 Capacity development options

Direct capacity development

In order to ensure effective and sustainable implementation and management of the proposed waterreservoir, improved technical and managerial capacities would be required in the areas as outlined in Table 19 below:

Table 25: Overview of direct capacity development options

Capacity development aspects Capacity development measuresManagerial needs

y Integrated management approaches to ensure inter-provincial and central/provincial coordination

y lessons learnt from other projects & provinces y regular working groups y initial guidance for implementation

y Application of grievance and redress mechanisms for local communities

y Training courses y Implementation support

y Sustainable environmental management of reservoir and surrounding area

y Application focused training courses y Implementation support/technical guidance

Technical needs y Alternative livelihood development and extension y Training courses on livelihood models and

extension approaches y Implementation support for extension services y Training on participatory and community focused

extension approaches y Technical operation and management of the

reservoir y Technical capacity support in the form of

implementation guidance and trainings

Institutional learning

y In the Vietnamese context projects such as the Tra Su-Tri Ton reservoir always had a dedicated management board in charge of planning, operation and management. While this is not yet in place for the proposed reservoir the expected objectives of the reservoir show the need for an appropriate water/irrigation management organization. There are numerous lessons learnt and best practices available in the Vietnamese context. These should be considered for the Tra Su-Tri Ton reservoir with its primary functionsoffreshwatersupplyandfloodregulation.

y In addition, strengthening the cooperation and direction of the State in managing and protecting sustainable use of natural resources should be considered in order to improve integrated planning and management between central and provincial level. This could include the consolidation of currently applied approaches towards inter-provincial water/irrigation management. Such consolidation could take place through stronger roles of the Southern Institutes for Water Resources representing central level interests.

y Adoption of lessons learnt and successfully applied livelihood approaches of other provinces should be considered.Thisincludesoptionssuchasfreshwateraquaculture,floatinggardensandlotusfarming.Such experiences are available from other projects (such as IUCN) and in other provinces (e.g. lotus farming in Soc Trang). Such approaches should be taken up into the already existing extension systems in order to support the implementation of these livelihood models through local communities

y In order to be able to make informed decisions relevant data and information needs to be made available.Strengthening(financial)datacollectionandanalysisallowsofferbetterdecisionmakingandincreasesaccountabilityofdecisionmakersinordertomostefficientlyspendavailablefunds.

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Impacts of climate change, especially prolonged droughts cause serious damage to agricultural production in the Mekong Delta. Consequently, a combination of non-structural measures, such as changing cropping systems and patterns or transforming production models, and structural measures, such as reservoirs, in order to increase the capacity of fresh water storage, is required. The projected measures within the frame of the Tra Su – Tri Ton reservoir project match these general requirements.

Generally, the overall water balance allows the operation of the reservoir as proposed from a hydraulic and hydrological perspective. It is assumed that the water volumes in the Vinh Te Canal are sufficient to fill-up the reservoir between Augustand November using gravity flow supported bytemporary pumping. However, different scenarioswith varying discharge rates in the Vinh Te Canal need to be considered, and especially the impact of water extraction from the canal on downstream areas in years with reduced discharge must be taken into account. It is considered as most likely that the projected extraction of water volume from the Vinh Te Canal will have negative impacts for areas lying downstream.

ThereservoirisfilledupusinggravityflowfromtheVinh Te Canal as far as possible, and pumping is used to maintain the water level until the fresh water supply starts. A constant use of the stored water during the dry season is assumed. Water levels and respective water depths are 1.00 m or higher if the water supply should be possible during the entire dry season. If the summer rice crop should be kept, thewaterlevelfromApriltoJulymustbesignificantlybelow 1 m. During that time no water supply would be possible, and this would significantly limit thefunction of the reservoir.

Due to ecological reasons, the Tra Su forest should not be included in the reservoir area. Dredging may mobilize pollutants that now are bonded in the subsoil. A transport with the water flow todownstream areas may have negative impacts on the Tra Su forest. Furthermore, costs for earth worksandaccordingfollow-upcostswillsignificantlyincrease the project costs if dredging is applied, and dredging will complicate the approval procedure since it requires the permission of the Prime Minister. Thus, dredging should be avoided and the Tra Su forest should not be included in the project area. Thus, the reservoir area decreases to 2,175

7. KEY FINDINGS AND RECOMMENDATIONS

ha and the maximum storage volume decreases to 70.470 · 106 m³.

A further alternative design using areas south of the TraSuforestresults inatotalareaof3,040 ha. Inthis case further constructions such as a hydraulic bypass (gravityfloworpressurepipeline) fromthearea north of the Tra Su forest to the area south of the forest is required. This induces higher costs but increases the reservoir area and in the consequence thepotentialbenefits.Thisalternativecouldnotbeconsidered in depth in this feasibility assessment.

Evaporation leads to the loss of water in the reservoir of up to 0.20 m per month. The resulting pumping tomaintainthewaterlevelissignificantandsoarethe required pumping costs.

Generally, the characteristic soil parameters in the project area show very small permeability coefficientsandthusthesubsoilissuitabletoretainwaterinthereservoir.Incomparisontotheeffectsof evaporation, loss of water due to infiltrationcan be neglected. In the proposed design, the structures are optimized regarding their location and their dimensions since existing elements such as embankments, canals etc. are part of the design. This minimizes construction costs. The proposed water inlet structures (sluice gates to replace the rubber dams, pumping stations) are sufficient forthe operation of the reservoir. The proposed width of 40 m and a jamb wall elevation of 1.50 m are sufficient. The discharge through the downstreamfour sluice gates is feasible to ensure the required flow to supply the surrounding areas. Generally,the width of the sluice gates could be reduced in termsofhydraulics.Theveryhighflowvelocitiesatthe downstream area of the sluice gates require a wide and massive absorption pool to avoid massive erosion, scouring, and thus a loss of stability of the construction.

The main results of the geotechnical calculation can be summarized as follows:

y The settlement of the projected embankment is 0.56 m.

y For the projected embankment base failure is not relevant.

y The maximum height of an embankment is 5.7 m.

y If a slope of 19.9° next to the embankment is exceeded, slope failure occurs.

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The computed settlement should be balanced by a super-elevation of the according embankments. This was included in the cost estimate. The risk of base failure limits the maximum height of the embankments. Thus, the water volume of the reservoir cannot be increased by heightening the embankments. Dredging is seen very critical from a geotechnical perspective since it increase the slope angle and the risk of slope failure.

Heavier structures such as sluice gates and pumping stations need to be constructed on deep foundations such a bored piles or displacement piles. Especially the lack of knowledge concerning the subsoil below parts of the western embankment is a cause of concern. More detailed soil investigations in a higher spatial resolution are crucial.

The slope of the embankments was proposed to be 1:1.5 and thus is relatively steep. The advantage of this design lies in the reduced required space. Especially due to hydrostatic loads and to a certain extend hydrodynamic loads, the slopes must be protected. Close-to-nature alternatives should be considered.

Compensation mechanisms for the loss of land or livelihood incomes of local communities are a key issue to ensure that these are appropriately compensated through loss of land or reduced incomes from livelihood changes.

It is crucial to strengthen inter-provincial, cross-border and national level coordination to ensure mitigationofpotentialnegativeeffectsandinclusionin integrated national, regional and provincial planning processes. In this context, capacity building should be considered.

Furthermore, the development of a detailed Environmental Impact Assessment or Strategic Environmental Assessments (SEA) in line with guidelines under the new Planning Law as well as guidelines of potential investors needs to be developed. Such a report can then reconsider scale, potential impacts, responsibilities as well as work measures to avoid negative impacts to the surrounding population and ecosystem, especially Tra Su Melaleuca Forest, but also downstream areas thatmightbeaffectedbywaterextraction..

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Generally, the application of a reservoir to provide fresh water supply in the dry season is a feasible measure tostrengthentheresilienceofaffectedareas.Toreachasufficientdegreeofefficiency,thereservoirmustexceed a certain size. The creation of such a reservoir goes along with extensive construction measures, suchasembankmentsandsluicegates,andthusrequiressignificantinvestments.Theselectionofasuitablelocationforthecreationofareservoircanreducethecostssignificantlyandmitigatepotentialdamagestothe environment.

However,thecreationofareservoirwithanefficientsizedoesnotonlyimplyextensiveconstructionworksand according costs, but also causes massive impacts in the environment and livelihood. Negative impacts for downstream areas due to water extraction cannot be precluded.

Thus, a detailed Strategic Environmental Assessments (SEA) is crucial. Relevant for both ODA support as well as under the new national Planning Law, this will then provide certainty on the above raised questions/concerns and assumptions.

Furthermore,afinancialassessmentbasedonacost-benefit-analysisprovidesanimportantdecisionbasis.After a general decision based on the Strategic Environmental Assessments (SEA), the dimensions and the designofthehydraulicelementsmustbeoptimizedtoreachthebestcost-benefit-ratio.

8. CONCLUSIONS

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Time of publication:October 2018

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Hanoi, 2018