needs report: appendix b

8/13/2019 Needs report: appendix B

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100-RG-PNC-00000-900008 | Summer 2010

Appendix BReport on Approaches to UWWTD

Compliance in Relation to CSOs in majorcities across the EU


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THAMES TUNNEL

NEEDS REPORTAPPENDIX B

LIST OF CONTENTS

Executive Summary 6

1. Introduction 8

1.1. Background 81.2. Scope of work 81.3. Methodology 81.4. EU City selection process 9

2. City Responses 122.1. Austria 12

2.1.1. Vienna 122.2. Croatia 14

2.2.1. Zagreb 142.3. Czech Republic 16

2.3.1. Prague 16

2.4. Denmark 192.4.1. Copenhagen 19

2.5. Finland 232.5.1. Helsinki 23

2.6. France 262.6.1. Lyon 262.6.2. Marseille 262.6.3. Paris 28

2.7. Germany 312.7.1. Berlin 312.7.2. Hamburg 342.7.3. North Rhine-Westphalia/Rhine-Ruhr (Emscher) 40

2.8. Greece 452 8 1 A h 4


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2.13.1. Stockholm 53

3. Summary and Conclusions 563.1. Large projects within the EU 563.2. Small projects within the EU 56

4. References 59

Appendix A CSO consenting/design approaches in the EU 68

A.1. General 68

A.2. Czech Republic 69A.3. Flanders 70A.4. Germany 71A.5. Italy 71A.6. Netherlands 72A.7. Spain 72


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List of Figures

Figure 1. Location and schematic layout of the Wiental-Kanal, Vienna (WienInternational, 2006) ...................................................................................................... 12

Figure 2. Schematic of RTC data flow for the sewer Network of Vienna (Teufel,2007) ............................................................................................................................ 13

Figure 3. Schematic of the Vienna sewer network RTC system (Teufel, 2007) ......... 14

Figure 4. Flood gate on the central sewer of Prague (Hrabak et al., 2005) ................. 17

Figure 5. Measured and predicted reductions in CSO volumes released to theCopenhagen harbour areas (Sorensen and Kofod-Andersen, 2005) ............................ 21

Figure 6. Sewer network of the Helsinki metropolitan area (Helsinki Water, 2009) .. 24

Figure 7. Water quality in Helsinki and Espoo (Helsinki Water, 2009) ...................... 25

Figure 8. The Marseille sewer network (Laplace et al., 2007) .................................... 27

Figure 9. WWTPs on the Paris sewer network (new/planned WWTPs shown withdashed lines), (Even et al., 2007) ................................................................................. 30

Figure 10. Storage volumes within the Berlin combined sewer system (Schroeder,2009) ............................................................................................................................ 33

Figure 11. The Rhine-Ruhr Metropolitan Area, Germany (Wikipedia, 2009b) .......... 41

Figure 12. Location of treatment works and restructuring of the Emscher sewersystem (Frehmann et al., 2008) .................................................................................... 41

Figure 13. The 'Rainwater Route' of the Emscher Region (Becker and Raasch, 2001)...................................................................................................................................... 42

Figure 14. Rainwater and infiltration projects in the Emscher Region (Becker andRaasch, 2001) ............................................................................................................... 43

Figure 15. Longitudinal section of the Emscher trunk sewer (Frehmann et al., 2008)44


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Figure 22. Real Time Control of the sewer network of Barcelona (Escaler Puigoriol,2009) ............................................................................................................................ 51

Figure 23. Detention tank in the sewer network of Barcelona (Escaler Puigoriol,2009) ............................................................................................................................ 52

Figure 24. Gates in the sewer network of Barcelona (Escaler Puigoriol, 2009).......... 52

Figure 25. The Real Time Control Process in Barcelona (Escaler Puigoriol, 2009) ... 52

Figure 26. Faecal coliform numbers at various sampling locations along Sant Sebastiabeach, Barcelona (CFU/100ml), (Escaler Puigoriol, 2009) ......................................... 52

Figure 27. Location of WWTPs in Stockholm (Stenroos and Katko, 2006) ............... 53

Figure 28. Profile and plan of the Ormen Project, Stockholm (Nordmark, 2002) ...... 54


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List of Tables

Table 1. Wastewater collection systems in EU Member States (EWWG, 1995) 9

Table 2. Large European Union cities (ranked by metropolitan population) 11

Table 3. CSOs permitting back flow to the Prague sewer network (Hrabak et al.,2005) 18

Table 4. Modifications to CSO83 on the Botic Stream, Prague (Kabelkova et al.,2007) 18

Table 5. Investment costs () for the three scenarios (Clauson Kaas et al, 2008) 22

Table 6. Operation and maintenance costs () for the three scenarios (Clauson Kaaset al, 2008) 22

Table 7. Simulated annual discharge ofE. coliunder three different dischargescenarios (Clauson Kaas et al, 2008) 23

Table 8. Simulated annual discharge of pollutants from the WWTP in under threedifferent discharge scenarios (Clauson Kaas et al, 2008) 23

Table 9. Statistics of the Helsinki sewer network (Helsinki Water, 2009c) 24

Table 10. Sources of BOD and suspended solids in the Hamburg sewer network(Abraham, 2009) 37

Table 11. Overflow volume reductions achieved by facilities of the sewer network inHamburg (Abraham, 2009) 38

Table 12. Odour management regime of the Schdlerstrae retention basin, Hamburg(Abraham, 2009) 40

Table 13. Wastewater volumes by sector in Madrid (GHK, 2006) 53

Table 14. Investment in wastewater treatment in Madrid (GHK, 2006) 53

Table 15. Summary of CSO abatement approaches in large cities of the EU


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Executive Summary

The report identifies and documents the way in which large European Union (EU)cities in several Member States aim to achieve or are achieving compliance with theUrban Wastewater Treatment Directive (UWWTD). Emphasis is placed on how thesecities are complying with respect to combined sewer overflow (CSO) discharges intokey watercourses, rather than wastewater treatment schemes (although some overlaphas been identified). Large EU cities were ranked based on their metropolitan

population size. Cities with a population equivalents in excess of 1 million were

prioritised for investigation. A thorough review of publications from journals,conference proceedings and other sources was undertaken and key experts fromacross Europe were contacted, in order to provide the most up to date information.

The main drivers in dealing with problematic CSOs are not only restricted to theircompliance with the UWWTD but also include complying with the Bathing WaterDirective and reducing urban flooding. Additionally, responses to either the UWWTDor National Laws transposed from the UWWTD vary quite widely between MemberStates depending on the region or water/wastewater managementstructure/organisation. Several cities have established a Master Plan for UrbanDrainage as a vehicle by which to review and address the existing and future issuesassociated with parts of their sewer networks (Barcelona, Hamburg, Prague, Zagreb).

The most common approach to resolving CSO issues was identified to be the additionof extra capacity, whether by the construction of detention tanks and/or trunk or

interceptor sewers (Athens, Thessaloniki). Within some cities the use of theseapproaches was complemented by the use of RTC (Barcelona, Lisbon, Marseille,Vienna, Zagreb). Several cities also combined both of these approaches with WWTPexpansion (Copenhagen, Lisbon, Paris, Prague) and/or sewer separation(Copenhagen, Hamburg). Two German cities were identified as utilising sourcecontrol techniques (SUDS/disconnection-infiltration, retention basins) alongside someof the more traditional approaches (Berlin, North Rhine-Westphalia). Only tworecent projects, located in Naples and Vienna, utilised tunnels in combination withWWTP expansion and RTC, respectively, although the use of tunnels is currently

being assessed in Paris. Helsinki and Stockholm were also identified as utilisingtunnels, but this was due to a range of historic reasons, not UWWTD compliance.Within smaller cities, a range of approaches was also identified, ranging frominterceptor sewers (Granollers, Spain and Steinkjer, Norway) and off-line storageb i (C I l ) h h l d SUDS (B d B


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conclusion, it is apparent that there is not a one size fits all intervention in dealingwith problematic CSOs, when trying to comply with the UWWTD or other drivers.


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1. Introduction

1.1. Background

The overall aim of this report is to examine the schemes that European cities areplanning or have implemented to comply with the Urban Wastewater TreatmentDirective (UWWTD). Specifically, the report will outline:

The UWWTD implementation actions of selected EU Member States;

A description of major city schemes for selected EU Member States.Emphasis will be placed on how the major EU cities are complying with therequirements of the UWWTD with respect to CSO discharges into key watercourses,rather than wastewater treatment schemes (although there is clearly some overlap).

1.2. Scope of work

The report will concentrate on specific schemes and key cities/rivers where CSOs areproblematic. The focus will be primarily the responses that have been investigatedand implemented to resolve these issues. The degree to which each member state hascomplied with the UWWTD will not be covered in detail.

1.3. Methodology

Information has been gathered for this report using the following methods:

Internet search to produce a list of the largest cities in the EU, together with theirassociated water bodies;

Preliminary internet literature search for documents relating to the UWWTDimplementation and CSOs;

Efforts to obtain Eureau document B4-3040/96/000173/DI, titled Stormwaterpollution control in the EU member states, via contacting Eureau direct and alsopersonal contacts the document could not be located;

Review of the Pennine Water Group Thames Tideway Study-Overview ofFi di (A hl d S i 2005)


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o 3rdInternational Conference on Sewer Processes and Networks, 2002 (Paris);o International Conference on Sewer Operation and Maintenance, 2002 (Bradford);

o 9th

International Conference on Urban Drainage, 2002 (Portland);o 6thInternational Conference on Urban Drainage Modelling, 2004 (Dresden);o 10thInternational Conference on Urban Drainage, 2005 (Copenhagen);o 7th International Conference on Urban Drainage Modelling and the 4 th

International Conference on Water Sensitive Urban Design, 2006 (Melbourne);o International Symposium on New Directions in Urban Water Management, 2007

(Paris);o Novatech, 2007 (Lyon);o

11

th

International Conference on Urban Drainage, 2008 (Edinburgh);

Identifying and contacting appropriate authors from papers derived from theabove conference proceedings;

Generating a database of primary and secondary personal contacts to approachfor information for particular member states/cities.

The latter three sources have yielded the most relevant and detailed documents andinformation. These have been collated and ordered by country/city to form the main

body of this report (Section B).

1.4. EU City selection process

The scale and age of wastewater collection systems varies across the EU and are

summarised alphabetically in Table 1. As can be seen, the UK has one of the oldestsystems, which is similar in age to those in Germany. The UK system also serves thejoint second highest percentage of population.

Table 1. Wastewater collection systems in EU Member States (EWWG, 1995)

Country% of population

served

% of urban areas served by

combined systems (estimated)

Age profile of collection

systems (where known)

Belgium 58 70 -Denmark 94 45-50 50% after 196020% after 1980

France 74 70-80 -Germany 90 67 74% after 1945

60% after 1963


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Additionally, approaches to the issuing of consents and permits to discharge, as wellas the design of CSOs, varies considerably within the EU. A review of approaches

used across member states is given in Appendix A.

In order to identify cities to focus on within this report, various criteria forcomparison were selected. This was primarily the city and metropolitan population(person equivalent, p.e.), or agglomeration size, as this approximately determines thetype and scale of schemes considered. London is the largest EU city, with a city

population of 7,556,900 (Table 2). It was therefore decided to focus on EU cities witha city and/or metropolitan p.e. comparable to London, but of no less than 1 million.Cities outside the EU were not included in the in-depth study, as the UWWTD wouldnot apply. Table 2 summarises the largest European Union cities and their associatedwater bodies; the agglomerations highlighted in bold are included within this report.

The latest European Commission (EC) Report in the authors possession (CEC, 2004),determines that only Austria, Denmark and Germany had fully complied with thedirective (the last questionnaire was conducted in 2007 and the next report is due in

2009 (Lenz et al.2007; CEC, 2008)). In 2005, Spain was being taken to the EuropeanCourt of Justice by the EC for failing to fulfil its obligations (GHK, 2006). Asrecently as 2008, France was under a similar threat (IHS, 2008) and in 2009 Italy alsofaced a written warning from the EC for non-compliance (Web4water, 2009). Assuch, activities being undertaken within large cities of these member states will beincluded in this report. Section C of the report summarises the overall main findingsand Section B provides greater detail on each of the previously identified large EU

cities.


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Table 2. Large European Union cities (ranked by metropolitan population)

Country City name Water bodies City

population

Metropolitan

population

Russia Moscow* Rr Moskva 10,382,754 13,500,000UK London Rr Thames 8,278,251 12,300,000(A)

Germany Rhine-Ruhr

area

Rrs Ruhr to south, Rhine

to west, Lippe to north

- 11,800,000 (B)

France Paris Rr Seine 2,188,500 10,000,000 (C)

Spain Madrid Rr Manzanares 3,213,271 6,100,000 (D)

Germany Berlin Rr Elbe/Spree/Havel 3,425,000 4,275,000 (B)

Spain Barcelona Rr Llobregat/Bess 1,615,908 4,250,000 (D)

France Lyon Rhne and Sane Rivers 472,305 4,415,000 (C)

Greece Athens Saronikos Bay 745,514 3,750,000 (E)

Italy Milan Rr Ticino/Adda/Po 1,294,305 3,550,000Italy Rome Rr Tiber/Aniene 2,724,347 3,500,000Italy Naples Tyrrhenian Sea 966,209 3,075,000 (F)

Germany Hamburg Rr Elbe/Alster/Bille 1,773,218 2,575,000 (B)

Portugal Lisbon Rr Tagus 499,700 2,550,000 (G)

UK Manchester Irwell/Medlock/Irk/Mersey

458,100 2,475,000

Poland Warsaw Rr Vistula/Baltic Sea 1,706,624 2,375,000

Hungary Budapest Rr Danube 1,702,297 2,300,000Austria Vienna Rr Danube 1,697,937 2,000,000 (H)

Sweden Stockholm Lake Malaren, Baltic Sea 814,418 1,989,422 (I)

Netherlands Amsterdam Rr Amstel (& IJ Bay) 752,911 1,930,000Belgium Brussels Rr Senne 1,080,790 1,850,000France Marseille Mediterranean/ Canal de

Marseille

839,043 1,500,000 (C)

Denmark Copenhagen Various waterways 613,603 1,390,000 (J)Finland Helsinki Gulf of Finland 578,126 1,299,541 (K)

Czech Rep. Prague Rrs Vltava/Elbe 1,233,211 (L) -

Greece Thessaloniki Rr Axios 360,000 1,200,000 (E)

Croatia** Zagreb Rr Sava 786,000 1,108,000 (M)* = non European Union shown for comparison only; ** = EU member candidate planning to


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2. City Responses

2.1. Austria

2.1.1. Vienna

Viennas sewer network is approximately 2200 km long (53,000 individual pipes),has five main catchment areas draining approximately 260 km2 with an averageimperviousness ratio of 50% and serves a population of 1.8 million p.e. (Nowak,

2007). Recently, Viennas RTC activity has become one of the best documented casestudies of urban drainage management introduced to comply with water protectionregulations. Recent developments within the network include large storage sewersalong the river banks of the Danube, Donaukanal, Wein and Liesing (Fuchs andBeeneken, 2005). Additionally, the construction of a detention basin close to the mainWWTP of Vienna is planned, with a total volume of approximately 255,000m3(Teufel, 2007). These are designed to minimise CSO spills to receiving water bodiesduring storm water episodes, as well as moderating the inflow to the WWTP.

At the end of 2006, a 3 km long, 30 m deep wastewater tunnel along the River Wien,the Weintal-Kanal, was completed. The Wiental-Kanal is capable of storing up to110,000 m3of waste water. In the event of heavy rainfall the Vienna Sewer NetworkControl sets the rate at which wastewater is discharged to the main WWTP.Additionally RTC is used to control the distribution and pumping systems, whichregulate the discharge of water and prevent pollution of the River Wien with diluted

wastewater (Wien International, 2006).


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o Local control devices to regulate flow and levels;o SCADA system to collect and display measured data;

o Central control system to facilitate decision making based onmeasurements and forecasts.

The process of data collation and control is illustrated in Figure 2 and Figure 3(Teufel, 2007). Within SeMaSys RTC the sewer network is reduced to approximately2200 pipes, in order to increase computational time. The model was calibrated usingmeasured data and uses Hystem-Extran software to generate rainfall-runoff. Thecontrol system is rule-based, but evaluated with the aid of fuzzy logic and the inputdata. Results from simulations (undertaken using ITWH-CONTTROL software) andreal situations are stored in a database for upgrading and self-learning (Fuchs andBeeneken, 2005).

Simulations for the left bank of the River Danube (known as LDS), using allavailable rain gauges revealed that for constant areal rainfall the mean reduction inoverflow volume achievable would be approximately 43,000 m3 (Fuchs and

Beeneken, 2005). Further analysis with loads simulated for an extensive rainfall eventshow that although nearly the whole system capacity was required for the diversion offlows, a reduction in CSO volume of 2.4% was possible. The LDS phase of the RTC

became operational in 2005 and the total simulated reduction in accumulated CSOvolumes for one year was estimated at around 30% (Nowak, 2007). The second phasecomprises the Donaukanal right bank main collector (known as RHSK-E), whichcame into operation in 2006. Evaluation results showed the retention volumeamounted to slightly over 40% of the previously discharged volumes (Nowak, 2007).The third and final phase, to be realised by 2015, comprises the integration of theLiesing and Wien storage sewers, as well as system optimisation. Currently, however,the system is not fully operational due to some failures in data measurement (Fuchs,2009c).


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Figure 3. Schematic of the Vienna sewer network RTC system (Teufel, 2007)

2.2. Croatia

At the time of writing, Croatia had not ascended to the EU. However it is a candidatecountry, after applying in 2003 and is expected to ascend sometime in 2010. Inresponse to this, the country is already implementing EU Directives and undertakingrelated activities in order to comply with relevant legislation.

2.2.1. Zagreb

The Zagreb sewer system serves approximately 1 million inhabitants and a largeindustrial sector. It contains more than 1300 km of public and approximately 1000 kmof industrial sewers. No WWTP currently exists, but this is being considered in future

plans. The sewer system serves various types of catchment (from natural to urban)across a range of slopes. Creeks from the neighbouring mountain, Medvednica, feed

into the sewer system. The network has very large conduits, but almost no CSOs(Dedus and Pavlekovic, 2005).

The main recipient is the Sava River, which divides the city and the sewer system intotwo separate systems it is anticipated that the WWTP will be constructed at theconfluence of these in order to treat flows from both systems In and around the city


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realised that any further investment in the sewer system or the WWTP, without firstconducting research, would be unwise.

'The Zagreb Sewerage System Optimization Project' (ZSSO), initiated at the end of1994, has established new standards in urban drainage modelling within Croatia.Using a Scandinavian methodology, based on continuous hydrological modelling,hydrodynamic description of flows in the system and a statistical evaluation of themain parameters representing sewer capacity and flow effects, the project utilises themodelling tools MOUSE and MIKE I (Dedus and Pavlekovic, 2005).

At the beginning of 1995 the first phase of ZSSO set out to collect all available dataon the present state of the sewerage system and to create tools for the development ofa master plan. The final goal of the project is to implement an engineering anddecision making tool for real time control (RTC), in order to provide an integratedflood protection system, reconstruction of the GOK and the construction of a WWTP.

Basic ZSSO project goals include:

o Comprehensive network data collection;

o Definition of remedial measures to improve the operation of the system;

o Establishment of principles for a master plan for rehabilitation and furthersewerage development;

o Definition of the standards for the protection receiving waters and theenvironment;

o Input for the future WWTP definition;

o Creation of a set of tools to collect data on system performance and for RTC;

o Establishment of a Zagreb Sewerage Real Time Control and ManagementCentre.

Achieving these goals relies on the following tools and principles:

o Distributed modelling of the surface storm runoff (FRC) and wastewater


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o Long-term runoff and pipe flow simulations, based on historical rainfallrecords, statistical evaluation of the hydraulic performance and environmental

impact of the present situation. In later phases of the project, feasiblestructural or operational alternative solutions would be modelled andevaluated through the comparison with the present situation;

o Feasibility assessment of the selected upgrade strategies, aimed at acost/benefit analysis.

Recommendations resulting from the ZSSO project to date include:

o Build up the retention volume of collectors;

o Achieve active outflow/retention control of the creeks from Medvednica;

o Design several overflows to the Sava River;

o Exclude the Bliznec and Vuger creeks from the GOK;

o Implement a strict maintenance schedule;

o Create a SCADA-based RTC system (Dedus and Pavlekovic, 2005).

2.3. Czech Republic

2.3.1. Prague

The main sewer system of Prague is combined and covers about 60% of the total cityarea. It consists of 2,360 km of sewers, 54,000 manholes, 140 CSOs and 19 pumpingstations. The sewer system is connected with the central WWTP, which has a designflow rate of Q = 6m3/s. Due to the large amount of inter-connections, the type ofstorage structures and the regular extension of the system, its behaviour is complex.Problem areas identified include the pollution of receiving waters (Vltava River) bycombined sewer overflows and the deteriorating condition of the system itself.Another problem is connected with several local separate sewer systems located onthe outskirts of the city (Hrabak et al., 2005).


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o Evaluate the main trunk sewers in catchments using MOUSE-HD,MOUSE-TRAP and MOUSE-NAM (Dedus and Pavlekovic, 2005);

o Evaluate the long term impact of the main CSOs on the Vltava river waterquality;

o Evaluate a final strategy for the time horizon 2015-2030: specify a finalurban drainage system in a digital form.

Results indicated primarily that the Troja Island WWTP would require expansion, butthat the existing structure of the sewer network (combined in the centre and separatedin the suburbs) could remain unmodified (Gustafsson et al., 2000). However, inAugust 2002 serious flooding hit Prague, which challenged this conclusion (Hrabak etal., 2005).

The Prague sewerage network, as well as the main WWTP, was hit by the floods.Rising water in the Vltava River flooded the WWTP and prevented the outflow of

wastewater. The system became highly overloaded due to the high water level in theriver, the closing of flood defence caps, the overflowing of outlets from the mainsewers beneath the city and direct runoff caused by the storm. Measures to remedythis disaster began immediately in autumn 2002. A great deal of attention was focusednot only on protective measures against floods caused by rainfall volumes, but also onmeasures to prevent the self-flooding of the city, caused by the combination of floodand urban waters forced into the sewer system (Hrabak et al., 2005).With repect to this, there are a number of projects being executed to improve the

performance of the sewer system. The following districts have been identified as thepriorities:

o Karln;o Holeovice;o Old Town, Lesser Town, Smchov and Podol;o Troja and Libe;o Other endangered areas (Zbraslav, Radotn valley).

Flood gates have been installed within the sewers (Figure 4) and CSOs are receivingmodification in these areas, including slight changes in tank geometry and theinstallation of pre-treatment devices. As far as could be identified, there is also a largeretention tank being constructed in the Karlin area (Pryl, 2009). Table 3 summarisesCSOs identified as having implications for sewer flooding and these have been


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Table 3. CSOs permitting back flow to the Prague sewer network (Hrabak et al.,

2005)

Further work has been undertaken to fully understand the impacts of CSOremodelling on receiving water bodies in Prague, but from a water quality

perspective. CSO83 on the Botic Stream (a drain in the central area of Prague) washeavily reconstructed between 2001 and 2005 (Table 4), (Kabelkova et al., 2007).Changes to throttling, increases to the critical discharge when an overflow occurs andchanges in the catchment, as well as overflow hydraulic characteristics have beenmonitored and simulated by the Prague Water Supply and Sewerage Company and theUDMP consultants (Hydroprojekt and DHI Hydroinform).

Table 4. Modifications to CSO83 on the Botic Stream, Prague (Kabelkova et al.,2007)


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Botic Stream has been monitored (heavy metal concentrations in sediments andmacrozoobenthos) since 1998. Simulation results for the reconstruction phases

revealed a gradual decrease in the average number of overflows per year, overflowvolume and duration and the amount of suspended solids discharged in the individualreconstruction phases. The average number of overflows possibly causing ammoniatoxicity was reduced by half (from 9 to 4.9) in phase II and nearly eliminated in phaseIV (0.4). However, the overflow volume, amount of suspended solids correlating toheavy metals and hydraulic stress were not significantly reduced until phase V in2005.

In addition to this, research on new types of CSO is being undertaken (Pollert et al.,2008). Within Prague, there is currently much of research being undertaken intoredesigning the sewer network and subsequently CSOs. The main drivers are thecreation of a new UDMP, reducing urban flooding and increasing receiving waterquality. However, a current limiting factor in the development of a final technicalmodel for the drainage system is a gap in legislation in terms of CSO overflows,although this is planned to be addressed in 2010.

2.4. Denmark

2.4.1. Copenhagen

The City of Copenhagen covers an area of approximately 90 km and has a populationof approximately 501,000. The Copenhagen sewerage system was established in

1857, with most of the present day system having been built between 1860-1910 Thesewer network now totals approximately 68 km, of which 90% is covered by acombined sewer system (the rest is covered by a separate system). The total annualamount of treated rain- and wastewater in the two main treatment plants (Lynettenand Damhusen) is approximately 90-100 million m3. In addition, there are 43overflow structures in action between 0-33 times a year the average discharge being13.7 times annually. However, this varies between CSOs near the harbour, whereinterventions have been implemented, and those areas awaiting development(Sorensen et al, 2005).

The extension of the Copenhagen sewer system has taken place in stages, each withtheir specific target:


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Brook to the southern marine recipient) and to lead a joint outlet sewer acrossthe island of Amager to the Sound. These considerations took into account the

receiving waters capacity to receive the wastewater;

The Lynetten treatment plant in the north of the island of Amager was builtand commissioned in 1980, when it was identified that the receiving waterswere unable to receive the wastewater. The extension, including installationsto remove nutrient salts at the Damhusen and Lynetten treatment plants, was

planned and implemented between 1987 and 1997. Sewer system plans nowclearly allow for the capacity of receiving waters and the environmentalauthority defines the requirements;

A number of new retention basin facilities were built from 1994 in order toavoid or reduce wastewater discharge to marine and freshwater areas duringhigh intensity rainfall events. The plants were dimensioned according to thespecific requirements of individual receiving waters set out by theenvironmental authority. The Sydhavnen facility (15,000 m3) utilises

comprehensive online management of gates and meters, which has improvedconditions in the inner harbour. The Utterslev Marsh facility (limited to thenorthern neighbouring municipalities) was supplemented with a constructedwetland system in 1998 allowing the mixture of wastewater and rainwater to

be treated before discharge to the nearby marsh. The East Amager facility(40,000 m3) ensures the requirement for bathing water quality can be met. It isthe first time that this has been made a primary requirement. During this

period, attention was increasingly directed to the sewer system's impact onground water and on conditions in lakes and streams;

From 2000, the frequency of CSOs to marine receiving water has been definedin terms of bathing water quality. The timeframe for objectives concerningsewer rehabilitation and measures to meet a certain quality with regard tolakes, streams and marine receiving waters is 2009.

The water quality has increased in the harbour, permitting the reopening of severalpublic swimming baths, 50 years after the last one was closed due to the levels ofpollution reaching the harbour. As some areas are still to be improved, a SCADA-based alarm system was implemented within the harbour, to warn of CSO incidenceslikely to cause highE. coliconcentrations. The limit was established at less than 1000E li 100 l f l h 5% f h b hi Thi i d


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0

200

400

600

800

1000

1200

1400

1600

1800

1995 1996 1998 1999 2000 2010

1000 x m3

Figure 5. Measured and predicted reductions in CSO volumes released to the

Copenhagen harbour areas (Sorensen and Kofod-Andersen, 2005)

Every combined sewer overflow structure has at least one level transmitter thatindicates when there is (risk of) an overflow event. The transmitters continuouslysend their information to the central computer in the Sewerage Department, and every15 minutes data of overflow volumes are transmitted to the Environmental ProtectionAgency (EPA) and Danish Hydraulic Institute (DHI). If an overflow occurs, an SMSis automatically sent to the guard duties of the EPA, Copenhagen Energy and DHI.The EPA decides on whether a warning should be issued. Once a warning is issued

the DHI uses a MIKE-model of the harbour area with inputs from the SCADA systemand predictions of direction of the current in the harbour. The model runs withconservative scenarios and on-line data of overflow and current for as long it takes toobtain a lower value than the critical level (500 E-coli per 100 ml for 12 hours). Whenthis level is reached the warning is removed. Data on the actual situation of the

bathing facilities can be seen by the public at any time during the bathing season onthe internet (http://www.miljoe.kk.dk/badeudsigt), (Sorensen and Kofod-Andersen,

2005).The next phase of intervention is rehabilitation to the sewer system of the newrestad district of Copenhagen and involves implementation of a separate sewersystem. The water will be divided into three streams: wastewater, rainwater fromcontaminated surfaces (roads, parking areas, etc.) and rainwater from clean surfaces

CSO Volume Reduction Measured and Predicted


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water and the efficiency of a newly developed mechanical treatment unit for urbanrun-off. A test area in the city centre was selected for hydraulic modelling using

MOUSE and the effect on bathing water quality was investigated using theCopenhagen Harbour MIKE-model. A 0.6 km area of the harbour area which is beingcompletely renewed was selected for conducting the modelling of three scenarios:

1) Interception of all surface runoff with the centralised wastewater system;

2) Interception of poor quality surface runoff to the centralised wastewatersystem and local discharge of good quality surface runoff;

3) Local discharge of all surface runoff.

For each scenario, the investment, operation and maintenance costs were calculatedand are given in Table 5 and Table 6.

Table 5. Investment costs () for the three scenarios (Clauson Kaas et al, 2008)

Size Scenario 1(M )

Size Scenario 2(M )

Size Scenario 3(M )

Retentionbasin (m3)

16,500 21.5 5,300 4.0 0 0.0

Pumpingstation (#)

14 0.2 14 0.2 23 0.3

Pipeline (m) 8,200 0.5 8,200 0.5 15,600 1.3

Local runofftreatment (#) 0 0.0 0 0.0 12 0.1

Sum 22.1 4.7 1.6

Table 6. Operation and maintenance costs () for the three scenarios (Clauson

Kaas et al, 2008)

Size Scenario 1(M ) Size Scenario 2(M ) Size Scenario 3(M )

Retentionbasin (m3)

16,500 0.02 5,300 0.01 0 0.00

Pumpingstation (#)

14 0.05 14 0.05 23 0.07


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2. In terms of bathing water quality, scenario 3 (local discharge of all runoff) is thebest solution. Furthermore, Table 8 shows the simulated discharge of pollutants for

the scenarios.

Table 7. Simulated annual discharge ofE. coliunder three different discharge

scenarios (Clauson Kaas et al, 2008)

Scenario 1 Scenario 2 Scenario 3

Local discharge of runoff (no. of cfu x 1012) None 0.044 0.085Discharge from CSOs (no. of cfu x 1012) 10.63 1.33 None

Table 8. Simulated annual discharge of pollutants from the WWTP in under

three different discharge scenarios (Clauson Kaas et al, 2008)

Scenario 1 Scenario 2 Scenario 3

COD (kg/year) 5,724 1,404 0Total nitrogen (kg/year) 774 190 0Total phosphorus (kg/year) 159 39 0

Considering the economic and environmental assessment, it has been decided toimplement scenario 2 (local discharge of good quality surface run-off and interceptingof poor quality surface run-off) for the whole harbour area. An overall deciding factoris the treatment efficiency of local surface run-off treatment units, which cannotensure sufficient removal of ecotoxic compounds (metals) to protect aquatic life.Presently, all new urban developments in the area will have to comply with thissystem. In future, the issue will have to be approached comprehensively for example

by reducing this diffuse pollution from vehicles and improving the removal ofecotoxic compounds. At the same time building permits will only be given if the roofmaterials do not include ecotoxic compounds such as Zn, Pb, Cr, Cu and PAH. Thissolution also supports the policy of the management of Copenhagen who want todisconnect as much rainwater as possible from its wastewater system to reduceoperational costs on pumping stations and wastewater treatment plant and also to

prepare for a change in rainfall pattern as a consequence of climate change (Clauson Kaas et al, 2008).

2.5. Finland


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Helsinki has both combined and separate sewer systems. The combined system coversmost of the downtown area with both wastewater and rainwater conveyed to the

Viikinmki WWTP. The combined system accounts for approximately 14% of thetotal length of the sewer network. In the separate sewer system, which covers the restof the city area, wastewater is conveyed via foul sewers (44%) to the ViikinmkiWWTP and rain water is conveyed in storm sewers (42%) directly to the nearestwatercourse (Helsinki Water, 2009c). The network consists of a range of differentsized sewers and tunnels, the lengths of which are summarised in Table 9.

Figure 6. Sewer network of the Helsinki metropolitan area (Helsinki Water,

2009)

Table 9. Statistics of the Helsinki sewer network (Helsinki Water, 2009c)

Diameter Length of Sewer % Diameter Length of Sewer %


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A major contribution to the protection of the Gulf of Finland (and consequently theBaltic Sea) is the Viikinmki WWTP, which has been operational since 1994.

Viikinmki treats all the wastewater from Helsinki, as well as runoff from thedowntown area, (Helsinki Water, 2009b). Most of the 120 million m3capacity plant islocated underground in rock caverns. Centralised wastewater treatment hascompletely eliminated previous nuisances including noxious odours and noise, caused

by now decommissioned decentralised WWTPs. The ventilation system from thetreatment process area leads all emissions to a tall chimney where they are rapidlydiluted in the atmosphere, leaving no disagreeable odours at ground level. Wastewatertreatment removes 95% of the oxygen-consuming substances, as well as 95% of

phosphorus. The current nitrogen removal rate is 80% in accordance with EUdirectives and the highest national standards. The effluent from the plant flowsthrough an outfall tunnel to a discharge area 8 km off Helsinki. Regular monitoring

programs of the sea approved by government authorities and conducted by the City ofHelsinki Environment Centre, include water, plankton, and bottom sampling. Seawater quality in the area has improved over the last 20 years, so that a stretch ofcoastline of more than 40 km, as well as the coastal archipelago, continues to be a

recreational area of good standard (Figure 7), (Helsinki Water, 2009).

Both the sewer network and the Viikinmki WWTP are controlled using RTC fromthe main control centre at the Vanhakaupunki raw water treatment plant (HelsinkiWater, 2009b). RTC of the sewer network is based on flow and pressure measure-ments in the network and over 110 wastewater pumping stations. The monitoringsystem enables disturbances in the network to be quickly rectified and energyconsumption to be optimised (Helsinki Water, 2009c).


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2.6. France

2.6.1. Lyon

Historically in Lyon, all wastewater and rainwater was conveyed within a combinedsewer network. Increasing development led to unchecked expansion of this system,creating a dense sewer network in the centre of Lyon increasingly under pressurefrom the volumes of rainwater being conveyed. Consequently, approximately twentyyears ago, political changes occurred to the way in which rainwater was managed. Aseparate sewer network was constructed for approximately 90% of the 2700kmnetwork, along with 8 retention basins and the initiation of the implementation ofsource control practises (such as infiltration). Such practises are applied to all newurban developments in the Lyon area. There are 8 WWTPs on the network, along with380 CSOs. An information gathering and modelling project was initiated in 1990 andfurther developed in response to the UWWTD and WFD. The project aims to identifyand limit flooding in inhabited areas and to reduce CSOs to the Rhone and Saonerivers (Volte et al., 2007).

The project consists of 6 stages:

Stage 1: Gathering sewer network data within the greater Lyon area (includingsewer flooding incidents);

Stage 2: Archiving the data in a GIS (CIGNET) and building a sewer networkmodel;

Stage 3: Calibrating the model using rainfall data and historic floodingoccurrences;

Stage 4: Simulating and assessing historic flooding events of 10-30 year returnperiods using CANOE modelling software for 650 km of network;

Stage 5: Prioritising locations requiring intervention (creation of the black

point list) to reduce spills to approximately one per month;

Stage 6: Using RTC to manage the CSOs (control of approximately 30 CSOsrepresenting 70% of majoroverflows).

St 1 t 5 h b l t d d t 6 (RTC) i d t b l t d i 2009


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particularly, beach areas. Therefore preserving good quality bathing water is ofprimary importance and the main driver is compliance with the revised 2006 Bathing

Water Directive (2006/7/EC). It is noted that the Marseille WWTP discharges itswater outside the bathing area and local studies of the currents have shown that thebathing area is not affected. Consequently, the quality of bathing water in Marseille isparticularly dependant on the effective functioning of the sewer network, rather thanthe effectivity of the WWTP (Laplace et al., 2007).

For several years the city of Marseille and currently, the Marseille Provence

Metropolis urban community, has implemented an ambitious programme in order toprotect the bathing areas from pollution from overflows from the foul and rainwaterdrainage networks (not pollution from the WWTP). The principal sources of pollutionwere identified about 30 years ago:

o Outflow of the small coastal river Huveaune arrived in the middle of thesouthern bathing area, transporting polluted water;

o Coastal development built below drainage networks discharged effluentsdirectly into the sea;

o Rainwater pipes collecting water used for cleaning urban surfaces duringdry weather discharged polluted water into the sea;

o Problems with effluents from pumping stations;

o Rainfall entering the main discharge pipe of the combined sewer networkbought with it pollution.


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During the last 30 years, numerous interventions have been implemented, which arenow realising positive results:

o The river Huveaune has been re-directed from its natural outflow by constructinga 6 km underground trunk sewer that arrives at the same place as the wastedischarged from the treatment plant;

o Systematic surveys were carried out on all developments bordering the coast inorder to remove all waste water discharges, either directly in the sea or inrainwater networks. A foul pipe was laid along the coast and all connections to it

from private properties had to conform to municipal standards;

o Surface water was redirected towards the foul network by establishing linksbetween the rainwater and foul systems. These links are equipped with automaticremote controlled gates, enabling the link to be closed in the event of heavy rainthereby avoiding saturating the foul network. 26 installations of this type have

been installed upstream of discharges into the sea from rainwater outlets in

bathing areas;

o The 3 largest discharge pipes of the combined network, initially static, have beenreplaced by remote controlled gates, allowing water to be maintained in thenetwork until risk of flooding occurs. These will then open when this level isreached;

o The overall electromechanical equipment is equipped with an electronic

surveillance system that enables rapid detection of malfunctions resulting inimproved RTC. Remote control of the same equipment enables the optimisationof storage capacities of polluted water in the sewerage network to avoid alleffluent overflows into bathing areas;

o The radar images of Mto-France and a network of 24 rain gauges spreadthroughout the town and connected to the remote control centre enable rainfall

events to be anticipated and managed using RTC.

Approximately 100 preventive closures occurred in 2004 and 2005 due to thisdynamic management process, ranging from half a day to one day each season on the22 beaches. On average, there were 5 closures per beach during the season, mainlydue to rainfall events (Laplace et al 2007)


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al., 2007). In response to this the capacity has been raised to 2.8m3/day to cover apopulation increase to 2015, as well as a 10% reserve capacity in case of a blockage

(SIAAP, 2007).The first evidence of CSO impacts on the receiving water bodies came to light in the1960s. However, it was not until the 1990s that reducing CSOs became a concern, asthe most visible dry-weather pollution had been reduced by a systematic constructionof WWTPs. In the Paris area, during rainfall events the daily flux of organic pollutiondominates the fluxes from WWTPs. Until the late 1990s, the 50 km long reach of theSeine inside Paris was permanently affected by high oxygen consumption accounting

for 112% of the flux upstream of the city. 20% of this demand resulted from CSOs(Even et al., 2007).

In 1995, the Syndicate of Sanitation of Paris (SIAAP) and the Water Agency ofSEINE Normandie established the Master Plan for the restructure of the centralParisian zone (Ile de France). A multi-criteria analysis (MCA) was conducted in1997, which resulted in a management plan time-scaled to 2015 covering WWTPs,

storage facilities and other treatment facilities discharging to the Seine. In 2003,SIAAP updated the plan to consider the evolution of technical and regulatorypractices in anticipation of the application of the WFD. The master plan forremediation was completed in SIAAP by February 2007 and divided into two phases.The first phase, conducted up to 2004, was to understand the current state of thesystem. The second phase, from 2004 to 2006, consisted of planning severalalternatives based on previous experience and establishing a further master plan forthe period 2007-2021. The objective of this plan is to minimise the impact on the

natural environment of discharges of urban waste water with l rainfall events of 16mm or greater. Within the MCA interventions examined are subject to the followingcriteria: natural environment - weighting of 40%; economic considerations - 35%weighting and stresses - 25% weighting (SIAAP, 2007).

The CSOs of the Paris sewer network have been widely studied within the PIRENSEINE program. The composition and fate of the urban effluents have been

characterized through sampling, laboratory experiments and modelling studies. ThePROSE model (based on the SaintVenant equations solved by a finite differencemethod, the Preissmann scheme, with bottom friction calculated by a Stricklerformulation) was designed to simulate the impact on the river of both permanent dry-weather effluents and of highly transient CSOs. It was also used to represent theimpact of Paris at large spatial and temporal scales


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Figure 9. WWTPs on the Paris sewer network (new/planned WWTPs shown

with dashed lines), (Even et al., 2007)

As well as focusing on the capacity of the existing WWTPs, 14 storage devices and 5WWTP specifically for the retention and treatment of rainwater are being considered.

The technical details for the 14 storage devices are:

10 reservoirs: 220K, 140K, 100K, 30K, 7.5K, 65K, 53K, 95K, 25K, 23K (a totalof 758.5K m3);

4 Tunnels: 148k, 35K, 50K, 27K cubic meters (a total of 260K).

The storage devices have been sized according to the following criteria:

Rainfall of 16 mm for a duration of 4 hours, representing a uniform depth ofwater across all of the SIAAP catchment areas or with a return period between9 and 12 months;


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upgrading treatment ( 1598 million) and the costs of new network (170 million),bringing the total investment to 3927 million. Finally, including the evaluation

project costs (12 million for flow management, 51 million for reductions inmicrobiology), as well as other operating costs (36 million), the overall master plancost could be in excess of 4000 million (SIAAP, 2007).

At the same time, RTC of parts of the Paris sewer system has been underdevelopment. RTC requires huge data acquisition and modelling undertakings inorder to build a comprehensive understanding of the sewer network and to optimisethe function of the networks features (gates, pumping stations) for any rainfall event.

In terms of water quality, several scientists have supported the integration of waterquality modelling into the RTC objective function. However, realistically, the

practical implementation of RTC only minimizes discharged water volumes (Even etal., 2007).

2.7. Germany

2.7.1. Berlin

In Berlin it is argued that compliance with the UWWTD (91/271/EEC) will bereached if measures are implemented according to the German engineering standardATV-A 128. In Berlin, drinking water is almost completely supplied by groundwaterlocated within the municipal area, with wastewater disposal occurring within the samemunicipal area. This creates an inevitable usage conflict between urban development

and pollution control and groundwater protection (Schroeder, 2009).The receiving waters of the Berlin sewer network, the Spree and Havel, are small andsensitive due to their small catchment areas (approximately 13500 km2 in total) andlow gradients (0.1% and 0.012%, respectively) generating low runoff rates. Theresultant low flow velocities create low self-purification conditions and thus are atrisk from pollution. During low flow periods, backwater accumulation can regrade therivers stage from flowing to stagnant, leading to heavy algae formation in summer.

These natural conditions are exacerbated by anthropogenic effects, such as urbanagglomerations.

The sewer network consists of 12 individual but combined drainage arms, arrangedradially to the watercourses and separated from each other by natural catchments.


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water tanks would be below 25% of the average annual rainfall runoff volume.Additionally, the pollution loads of COD, BOD5 and TSS of the discharge would be

below 20% of the average annual load of the rainfall runoff. These requirements arebased on the German engineering standard ATV-A 128, but are even more stringent,due to the previously identified sensitive nature of the receiving waters.

To achieve these levels, Berliner Wasserbetriebe (the local utility for water andwastewater services) has established a programme of measures to upgrade thecombined sewer system. The programme will ensure compliance with the legislationuntil 2020. It includes the following measures (in order of priority):

o Monetary incentives for green roofs and SUDSs on private properties;

o Unsealing of impervious surfaces and implementation of decentralisedSUDS (where possible);

o Full utilization of the static in-pipe storage capacities by heightening CSO

crests (taking into consideration flood prevention);o Implementation of actuators (weirs, sluices, throttles) for local RTC;

o Construction of additional stormwater tanks;o Increasing flow (pumping) to WWTP above usual wet weather inflow (if

the treatment capacity is available).

Due to the utilisation of a combined sewerage network and low topographic gradientsin Berlin, all outflow from the network and consequently in-pipe storage capacities,are controlled by pumping stations. These stations deliver the wastewater to thetreatment plants and act simultaneously as variable throttles in case of rainfall events.When exceeding the maximum pump capacities the combined water is retained withinthe sewer network until a critical level is reached and a CSO occurs. However, due tothe large size of the conduits and the very low sewer gradients, a high storage volume

is present. Depending on the size of the sewer, between 1,200 m and 12,500 m ofstorage space can be utilised. These figures correspond to a minimum specific in-linestorage volume of 3 m per 0.01 km of impervious area and a maximum of 65 m per0.01 km of impervious area. The total in-pipe storage volume accumulates to adimension of 125,000 m, which corresponds to an average specific volume of 15 mper 0 01 km of impervious area In addition 25 750 m of storage is available in the


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Figure 10. Storage volumes within the Berlin combined sewer system (Schroeder,

2009)

Further activation of in-pipe storage is realised by local actuators within the sewernetworks. Since 1996 a movable weir has operated within the main collector of thecatchment Berlin IX. The sewer is 3.07 m wide and 2.30 m high. The weir isactivated in case of a high intensity rainfall event and retains approximately 3000 mof combined water. A position sensor within the hydraulic cylinder of the weir, aswell as upstream and downstream level meters, measures the necessary process data.The control strategy limits the flow towards the pump station to the design flow(twice the dry weather peak flow) by activating the weir. If the critical upstream water

level is reached the weir is lowered to maintain this level. When the critical waterlevel is exceeded, the sewer cross-section is completely opened to avoid flooding. Atthe end of the rainfall event the flow towards the pump station is once again restrictedto the design flow until the collectors have been emptied.

A further alternative store for combined water has resulted from the modification ofsewer overflow conduits. Originally the conduits only functioned to convey

discharges from CSOs to receiving waters. Two modification projects have beenimplemented in Berlin. Firstly, they are operated as sewers with storage capacity andoverflow. Due to the wide and flat catchments, these overflow conduits can be verylong and therefore provide high storage capacities. In the centre of Berlin (the districtof Tiergarten) there is one sewer where the overflow crest was installed as a movablel i b d Thi l l t t i d t t l th t l l ithi th fl


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benefit of a fully automated global pump station control (Schroeder and Pawlowsky-Reusing, 2005; Rouault, 2008). However, due to operational boundary conditions, the

current potential of applying global RTC is rated as low. Currently, in the case ofclearly regional storm events, manual global control of the pump stations is appliedby the operators in the central control room.

2.7.2. Hamburg

The city of Hamburg is located on the banks of the river Elbe and its small tributarythe Alster. It covers an area of 750 km2. The metropolitan area has a total population

of 2.4 million people. Urban drainage in the city dates back to 1843 and includescentralized sewerage and water supplies. Today the city operates a sewer system ofabout 5240 km. There are 1300 km of combined sewers, 1850 km of foul sewers and1600 km of storm sewers. Most of the combined sewer overflow structures are locatedalong the small river Alster and its canalized tributaries, although the main outletstructure of the system is situated on the Elbe (the Hafenstrae pumping station,discharging 11 million m3 in a wet year). The river Elbe is the main waste-load

carrying stream in the area and the only water body suitable for taking treatment planteffluents and greater combined sewer overflow discharges. However, most of thepollutant load of the river Elbe originates from third party states or countries,therefore for decision making in Hamburg the Elbe ranks lower, in terms ofconstruction priorities and quality goals, than the Alster (Abraham, 2009).

Due to the flat topography in the Elbe estuary, 190 pumping stations are operated forsewage collection. Smaller WWTP have operated in Hamburg since the early 1900s.

However, wastewater disposal in terms of sewage treatment was first provided for thedowntown combined area at the end of the 1950s. This began with the construction ofthe Hafenstrae pumping station, located on the river Elbe and the Khlbrandhft-

Nord WWTP, situated on a peninsula on the south bank of the river. In the 1960s,after post-war reconstruction and sewer system repair, the sewerage departmentembarked on a staged long term sewerage improvement program, known as thedrainage Masterplan. A total of 767 million has been invested in treatment plant

expansion and interceptor construction. The main objectives of the master plan wereto:

o Improve the total sewer system performance in terms of: Public health aspects (foul flows); Flood control aspects (storm flo s);


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o Adjust the sewer system so that urban flooding is avoided at least on a 5-year frequency interval;

o Reduce the pollutant load to the receiving streams in order to balance thesystem at a eutrophic level (thus particular control of phosphorusemissions).

These objectives were defined as being achievable by undertaking:

o The construction of new interceptors for sewage transport to centralize

waste water treatment to the Khlbrandhft-Nord WWTP;

o The shutdown of smaller treatment plants discharging into small waterbodies with insufficient waste load carrying capacity and the expansion ofthe Khlbrandhft-Nord WWTP to meet requirements of incominglegislation;

o

The development of a wet weather pollution control programme, focussingon CSOs, treatment plant efficiency during and after a high intensityrainfall event and storm sewer runoff.

Activities undertaken during the master plan evaluation stage included the use of datacollection and computer analysis. The actual capacity of the sewer system and theexisting water quality situation in the receiving waters were evaluated with the help ofmathematical models. A computer model (based on the US EPA SWMM) was used

for the flow calculations and sewer system capacity analysis, due to the large andcomplex structure of the network, as well as the flat gradients, which produced back-water situations even under dry-weather flow conditions. The whole project,including sewer system data collection, took about 6 years to complete. Rainfallrecords, collected over decades, had to be analysed to derive rainfall-duration-frequency relations. The records were digitized and processed on a computer fordesign storm evaluation and later continuous flow simulation. A flow measuring

programme was established in the sewer system to facilitate model calibration andverification. Two distinct events were identified from this data: the first a first flushevent and the second a dilution event. Eventually, the mathematical flow model wasinstalled on the city computer and staff of the planning department trained to use themodel for sewer planning work.


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360,000 m3/d. In comparison with other cities this could be considered small and ismainly due to heavy industry and the oil refineries in the harbour area operatingindependent treatment plants.

Wet weather flow in the downtown district is generated from an impervious area ofabout 30 km2, consisting of house roofs, street surfaces and car parks. For 85overflow chambers, flow that cannot be handled by the trunk sewers is discharged tothe river Alster and its tributaries. The flow measuring programme revealed thatapproximately 4 million m3 of combined sewage was spilled by the 85 overflow

points into the Alster and its tributaries each year. The old trunk sewers of the

combined system are laid with grades of 1:3000 or less and lead to the mainHafenstrae pumping station. Dry weather flow and up to 7 m3during wet weather is

pumped over to the Khlbrandhft-Nord treatment plant. To avoid flooding in thedowntown area, during wet weather a storm water outlet to the river Elbe, protected

by tide gates, is operated in addition to the pumping station.

Construction of the interceptor system began in the 1970s and in 1982 major parts

became operational, with the foul flows from the northern districts of the city beingconveyed directly to the Khlbrandhft-Sd treatment plant. Dry-weather flow levelsin the trunk sewers of the combined system dropped, resulting in online storageavailable for storm flow. Subsequently the Hafenstrae pumping station became moreeffective in handling combined flows originating from the downtown area. As such,the pollution control benefits of the 15 year interceptor-construction-program becameapparent.

Based on computer runs for the 1-year and 5- year design storms a flow capacity planwas prepared. The plans include, for each sewer reach in the system:

o The actual through flow relative to the flow capacity for the reach (calculatedfrom the cross sectional area of the profile and the sewer slope);

o For each node in the system, the maximum water level relative to the sewerdiameter when flowing free, or relative to the difference in height between the

sewer crown and ground elevation when under a surcharge condition.These plans serve as valuable instruments in all kinds of sewer planning and areregularly updated. The sewer capacity analysis revealed that the followingdeficiencies existed in the historic system:


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Table 10. Sources of BOD and suspended solids in the Hamburg sewer network

(Abraham, 2009)

BOD (% ) SS (%) Source48 18 Residual sewage in the sewers during DWF25 9 Foul flow during high intensity rainfall events15 44 Surface runoff12 29 Sewer deposits

To overcome the above areas of deficit and to meet the master planning objectives,relief flow capacity was installed, 80 flow restrictions eliminated and the overflow

volume of a 1-year storm abandoned. In addition, it was determined that the masterplan objectives could be achieved by assessing a range of additional options,including:

o Advanced sewer separation;o Relief trunk sewer construction;o Retention basin construction;o

Pumping station and force mains instead of trunk sewers;o A combination of the above.

Advanced separation collects the less polluted flow from roof surfaces separately anddischarges it using:

o Storm drains into receiving waters;o On-site detention and infiltration facilities;o Storm water reuse facilities for toilet-flushing or lawn-sprinkling.

Advanced separation is effective where the water quality goal cannot be met bytreatment and storage of the combined sewage flows alone. In Hamburg this is beingutilised for some of the canalized tributaries of the Alster.

Relief trunk sewer construction can prove advantageous when:

o

The WWTP can handle additional flows;o Selective overflowing is utilised to convey peak flows away from sensitive

receiving waters to water bodies with a larger carrying capacity.

In consideration of the tr nk se er net orks e isting feat res s ch as poor slope a


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performance of the system. Therefore, it was identified that a combination ofadditional retention and discharge capacity would best fit the needs of the Hamburgsewer system. A solution was developed based mainly on gravity flow in a newsystem of transport sewers, laid about 10 m below the existing trunks andinterconnected using drop-shafts. The transport sewers serve as conveyance andstorage elements. In addition to the storage volume of the transport sewers retention

basins were also constructed in the vicinity of the drop-shafts (so that they could alsobe used for dewatering the basins).

The resultant highly interconnected combined sewer area is subdivided into smaller

catchments with an approximately 60 minute flow time between drop shafts. Acomparison based on dry-weather computer simulations between the old and the newsystem determined that the total volume of sewage resulting from the dry weatherflow in the sewers would be reduced from 110,000 m3to 40,000 m3, thus reducing thetotal pollution-causing potential of the system. Contributions to overflow volumereduction from facilities on the entire network are broken down in Table 11.

A detailed computer simulation revealed minor overflows in the region of 15,000 m3,due to an uneven distribution of flow and storage capacities over the whole system. Itis anticipated that system optimisation will eliminate these overflows. By introducingRTC it may be possible to collect and transport the bulk pollution load to the WWTP.Analysis of BOD/COD data from 1981 (prior to the start of operation of the firstinterceptors) and 1988 identified that without the interceptors in operation the wet-weather input load is generally less than the dry-weather load, whereas with theinterceptors in effect the opposite is true. Not only the waste load transported in the

sewer system improves, but also the overflow volume is drastically reduced. In 198884 % of the annual rainfall-runoff of the downtown combined area was interceptedand conveyed for complete treatment.

Table 11. Overflow volume reductions achieved by facilities of the sewer network

in Hamburg (Abraham, 2009)

Facility Overflow volume reduction (m3)

Hafenstrae pumping capacity 7Khlbrandhft-Sd (WWTP) pumping capacity 10Safe in-system storage 150,000Retention basin storage 125,000Interceptor sewer storage 80,000Transport sewer storage 100 000


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Standard procedures for retention basin design in Germany call for area specificrectangular storage volumes of 20-30 m3per 10,000m2of impervious area. To ensurea sufficient settling and primary treatment rate the basins surface hydraulic loadshould be limited to a value not greater than 10 m/h and the horizontal through-flowvelocity of the basin should not exceed 0.05 m/s. Additionally, to achieve reasonablesedimentation rates, the residence time in the basin should exceed at least 20 minutes.Based on these design criteria Schdlerstrae would have had a volume of 4000 m3,which would have violated water quality objectives (overflow frequency in the rangeof one event per year). Consequently, simulations were undertaken for the 1-yeardesign storm and determined an overflow volume of 6250 m3. Analysis of monitored

overflow data between 1966 and 1977 yielded 18000 m3

. In consideration of the factthat the total impervious area would be reduced by applying advanced sewer systemseparation, a continuous flow simulation, covering a rainfall period of 10 years, wasconducted using an estimated retention basin volume of 7400 m3. Simulations(incorporating separation) identified that a storage volume of 70,000 m3was a goodestimate.

The retention basin site is located in a commercial area which was already beingutilised as a parking facility. Therefore the basin was designed to be a deep circularshaft with an inner cylinder housing dewatering pumps. Operation of the basin is asfollows. When the capacity of the trunk sewer draining the basins catchment area tothe interceptor (Kuhmhle) is fully utilised, the retention basin begins filling. Theflow enters the basin tangentially on the bottom of the circular tank from a flowdividing structure on the trunk via a vortex drop-shaft. The basin fills with a swiftlycirculating flow, which concentrates sediments on the bottom of the tank as a result of

the because of the so-called tea-cup effect. When the tank is full, it overflows to aformer small natural ditch (the Gehlzgraben), which is now utilised as a storm sewerto the river Wandse. The basins input and overflow structures are designed to handlea through-flow of 30 l/s per 10,000m2of impervious area, giving a flow of about 4m3/s; for this flow the retention basin provides primary treatment.

During very high intensity rainfall events the surplus flow conveyed in the trunk

sewer will be spilled directly via a 16 m long trunk sewer overflow to theGehlzgraben. At the end of the event, when sufficient capacity is again available inthe trunk sewer, pumps start the dewatering process. Three pumps of 0.3 m3/s are

provided and it takes about 7 hours to dewater the tank. During the end-phase ofdewatering one or both of the stand-by pumps are activated for recirculating theresidual tank volume and for scouring the bottom sediments After dewatering is


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heavy rainfall events will be 16.5 m/s instead of the 30 m/s at present (Frehmann etal., 2008).

Figure 11. The Rhine-Ruhr Metropolitan Area, Germany (Wikipedia, 2009b)

Figure 12. Location of treatment works and restructuring of the Emscher sewer

system (Frehmann et al., 2008)


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new sewer network ready by 2014/15 (Geretshauser and Wessels, 2007). This willsubstantially reduce the number and frequency of CSOs required. Future plans for thearea also include:

o Improvement of rainwater treatment (for example, infiltration of rainwater atsource, where possible);

o Reduction of municipal, industrial, trade, mining and polluted rainwaterdischarges. (Herbke et al., 2006)

In terms of charging, a membership fee is paid, which is dependent on the quantity

and quality of sewerage and rainwater being discharged. For example directdischargers pay directly to the Emscher Association, whereas households arerepresented through municipalities (democratic legitimisation). As such thecharging system already incorporates the polluter-pays principle and cost recovery inthe Emscher River Basin ranges from 96.9% to 107.2% (Herbke, 2006).

It is estimated that the overall wastewater management restructuring of the 865 kmEmscher catchment area will cost around 4.5 billion (Frehmann et al., 2008).Subsidies of 4.5 million were provided for the Emscher region for theimplementation of rainwater harvesting and infiltration projects up to 1999 knownas the Rainwater Route (Figure 13). The subsidies amounted to 5/m of imperviousarea disconnected from the drainage system. Since 1994, 18 towns have participatedwith a total of 82 different projects and 47 projects have been or are beingimplemented (Figure 14). One such project is covered in Gruning and Hoppe (2007),

but is not reviewed in detail here. These pilot disconnection programmes are

centralised into a GIS known as the Stormwater Management Information System,SMIS, based on the Open Geospatial Consortium (OGC) standard. SMIS allowslocal authorities to easily identify feasible disconnection measures to implement inother areas, as well as calculating the percentage of an area with potential fordisconnection (Geretshauser and Wessels, 2007).


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Figure 14. Rainwater and infiltration projects in the Emscher Region (Becker

and Raasch, 2001)

The rates of disconnection achieved within the various schemes exhibit extremevariability. In densely populated areas, in the case of multi-storey apartments forexample, the rate of disconnection is only 2 to 3 %. For many schemes involvingcommercial projects, site pollution still exists and therefore resulting additional costsmake disconnection financially infeasible. Higher levels of disconnection can beachieved, however, in the case of larger individual commercial sites and in the case of

land owned by housing associations. Here, disconnection rates of 50 % or more canbe achieved. In addition, the provisions implemented are concentrated on asignificantly smaller area than in residential areas involving scattered individualschemes. A disconnection potential of 10% 21 km2 on average of the imperviousareas in the Emscher region appears to be realistic in the long term when the completerange of schemes is implemented. With this disconnection potential, the flood peakflow in the tributaries of the Emscher could be reduced by as much as 40 %, in thecase of minor floods with a two-year return period. The resulting significant reduction

in the flow-erosion of the bed of the watercourse is of immense ecological importancefor the tributaries of the Emscher.

As well as these disconnection activities, the main component of the restorationscheme is the large underground trunk sewer which has been under construction


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important operationally as different pumps allow the wastewater flows to be divertedto different sewers: the incoming wastewater flow from Dortmund to Gelsenkirchenwill be distributed to the existing Bottrop sewer and/or the new Emscher sewer, whichconveys flows to the Bottrop and KLEM wastewater treatment plants, respectively.This results in a number of options for flow control.

Operation of such a critical infrastructure, serving several millions of people posesparticular challenges. As such, Frehmann et al. (2008) undertook an integratedsimulation of the entire system. Treatment plants were implemented using theSIMBA simulation for wastewater systems, rainfall-runoff modelling was provided

by MOMENT (previously established by the Emscher Association) and the trunksewer was modelled using the US EPA SWMM5. The integration of these modelspermitted a range of automated operational control scenarios to be investigated acrossthe entire Emscher wastewater system. An example of this is illustrated in Figure 16,where the impact of WWTP management scenarios on COD have been simulated.

Figure 15. Longitudinal section of the Emscher trunk sewer (Frehmann et al.,

2008)


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Figure 16. COD for 4 WWTP control scenarios on the Emscher sewer system

(Frehmann et al., 2008)

Further work will be undertaken to include a multitude of rainfall scenarios (forexample, the non-uniform distribution of rainfall of different characteristics), as wellas scenarios covering the future development of the population in this highly

populated area. The value of increasing base flows for CSO abatement usinghydropower gate operation via RTC has also been researched for the Westphalia area(Achleitner and Rauch, 2007).

2.8. Greece

Most cities in Greece have separate sewer systems, so CSOs are rare. A commonproblem is the illegal connection of stormwater sewers to foul sewers. However, bothAthens and Thessaloniki have combined systems in the old city centres. There are no

plans to change this, as any reversal would be economically and technically

unrealistic (any excavation triggers interest or opposition from archaeologists thatwould severely delay implementation). However, certain interventions are proposedfor each city. These aim to separate the initial runoff of each rainfall event and drive itto the existing WWTP. This is being undertaken in order to reduce pollution loadsending in the sea; the final recipient in both cases (Bensasson, 2009). These


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treated. For flows Q/Qfull > 72%, the overflows discharge through two differentroutes:

i. Through existing overflow discharge structures (, , and ) to theKifissos river (at present this is covered for several kilometres upstream theriver mouth, with a major road running on top of it);

ii. Through the existing overflow discharge structures (1, 2 and H) to theProfitis Daniil stream which discharges to the Kifissos River.

However, one overflow discharge structure (H) and the connection pipeline to theProfitis Daniil stream do not operate adequately due to a lack of capacity. Moreover,this overflow discharge structure serves the existing combined sewer system of thecentral areas of Athens (Syntagma square, Akropolis etc). Therefore, the Ministry ofEnvironment and Public Works is undertaking (with ENM) a project to design adiversion of the Kyklovoros. This will lead the overflows directly to the KifissosRiver (instead of through the Profitis Daniil stream). The diversion of a Q = 170 - 270m3/sec from the Kyklovoros is considered very significant for flood control and

pollution alleviation in the centre of Athens (Bensasson, 2009).

2.8.2. Thessaloniki

The sewerage system of Thessaloniki covers an area of 77.5 km2 and serves apopulation approximately 1,200,000. The network comprises separate sewerage andstormwater systems, as well as some combined sections (in the centre of the town

covering 24 km2

) and a WWTP at Kalohori.

The combined sewerage system discharges to the Main Sewerage Collector(Kyklovoros or KAA), which is 16 km in length and was constructed in the 1980s.The Kyklovoros discharges to the Wastewater Treatment Plant. During intenserainfalls, the overflows discharge to the sea (Gulf of Thessaloniki / Thermaikos).There is one single overflow spillway (2 m in length) on the Kyklovoros and sooverflows discharge through an existing submarine pipeline to the sea (next to thetouristic area of the White Tower). When extreme overflows occur, a second pipelineis used which discharges to the sea at another location (New Beach).

The sewerage system of Thessaloniki, however, cannot cope with very intense rainfalle ents In addition d e to the landscape/basins of the area storm ater o erflo s


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o Alleviating pollution/discharges to the sea.o Facilitating maintenance works on the Kyklovoros or the second

collector.

In practice, the second collector also serves as a tank for the interception ofstormwater flows and the attenuation of peak flows to the waste water treatment plant(Bensasson, 2009).

2.9. Italy

2.9.1. Naples

The UWWTD was transposed into Italian law through the National Directive152/1999, which was published on May 11th, 1999. However, its complete fulfilmentis still far from being achieved, particularly in Southern Italy. However, there are anumber of features of the Neapolitan sewer network designed to deal with CSO spills.Most of the main sewer system is comprised of tunnels, due to the particular urban

context (steep slopes, dense urbanization and a large underground infrastructure). Theprinciples of sustainable drainage are not heavily utilised by the Neapolitan CityCouncil.

Within the tunnels, drop structures are quite frequent with drop heights as large as 80m. For this reason most of the structures are vortex drop shafts. Tunnel ventilationwas not carefully addressed during design. Instead, the installation of airtight inlets to

prevent the odour from escaping from the sewer during dry weather condition is

common. Additionally, in relation to odour, only the most recent installations haveaddressed this issue. Odour control was generally realised by inducing slightlyreduced pressure within the WWTP. Odour neutralization is essentially achievedthrough a two-stage chemical process (oxidation + neutralization of residual) to dealwith large concentrations of organic gas (i.e. HS or H2S). When applied, the odourcontrol operates during the entire working cycle. One of the latest installations on thesewer network in Naples is the Impianto di Coroglio. Its main features include

preliminary wastewater treatment, such as screens, sand traps, roto-sieves (illustratedin Figure 17 and Figure 18), which then pump the effluent to the main WWTP via a12 km long tunnel. The design discharge is 22,000 m3/per hour (approximately500,000 p.e.) and the plant is equipped with noise and odour control.


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Figure 17. Sand removal at Impianto di

Coroglio, Naples (Gisonni, 2009)

Figure 18. Roto sieving at the Impianto

di Coroglio, Naples (Gisonni, 2009)

RTC is not currently being applied extensively. A few pumping stations are equippedwith automatic systems aimed at managing emergency conditions. Additionally,debris screens and sediment traps are often built, but they suffer from a systematiclack of maintenance. Furthermore, no flushing systems are in operation due to: (i)steep slopes that guarantee adequate self-cleaning velocities; and (ii) water shortages,

meaning there is little spare capacity to flush the sewer channels. Flushing gates werenot installed within the system (Gisonni, 2009).

2.10. Netherlands

2.10.1. Rotterdam

The main drivers for CSO reduction in the Netherlands are national legislation forsewer systems, termed basis inspanning (basic level of reduction) and Waterplan 2(plans from the Municipality and the Waterboards). These focus on working withwater for an attractive city. The main technique used is RTC, to reach the basic levelof reduction of CSO spillages, costing approximately 1 million. However, in thecentre of Rotterdam a 10,000m3storage tank has been constructed, at a cost of 10.5million. Smaller tanks are also being planned but are not yet under construction.Additionally, small scale SUDS techniques are used. Odour problems are not

addressed under the schemes, but if future odour problems did occur these would bedealt with by additional measures. Implementation of the above schemes has resultedin a certain degree of good surface water quality and less flooding (Goedbloed, 2009).

2 11 Portugal


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during first flush effect, have led to the development and implementation of specificsolutions. Storage structures have frequently been built into the network (off-line orin-line storage) and flow control devices have been adopted for drainage system

inflows (Figure 20). These consider the acceptable average dilution for discharges inwater resources receiving treated effluents or the maximum number of alloweddischarges per year.

Figure 19. The sewer network of Lisbon

Drainage sub-systems in Lisbon (Alcntara, Beirolas and Chelas), particularly theAlcntara sub-system, are large combined sewers, making the transformation of

existing combined sewers into separate sewer systems a virtually impossible task.Thus, the Alcntara sub-system constitutes a representative example of the largecombined sewer paradigm, with inflows to the WWTP from the Alcntara sewerchannel and remaining inflows arriving at waterfront station of Largo Chafariz deDentro Algs, through pumping carried out at pumping stations. At present theexisting systems are inadequate and inefficient.

A l i d 160 illi i b i d i h di d i


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As a result, an estimated 160 million is to be invested in the upgrading and extensionof sewer networks and WWTPs up to 2012. Interesting challenges arise from thetypes of construction, cross-sectional range, tidal influence, number of CSOs and the

areas topographic profile. The main investment activities include remodelling theAlcantara WWTP (Figure 21) and the construction of the Largo Chafariz de Dentro-Terreiro do Paco-Cais do Sodre-Alcantara interceptor sewer system and six associated

pumping stations, using trench-less techniques (tunnel boring). In addition to this aWWTP water reuse project is planned (similar to that already in operation in themunicipality of Mafra within Lisbon, where gardens are watered using treatedeffluents from the Mafra WWTP). A final project covered by the investment will be

the implementation of RTC to facilitate performance modelling, receiving waterimpact assessment and maintenance cost optimisation (Almeida, 2009).

2.12. Spain

2.12.1. Barcelona

The drainage system within Barcelona experiences a rainfall regime with highintensity events. In addition the catchment contains both high mountains and flatcoastal areas with a high population density and a high percentage of impervious land.This combination has resulted in historic floods and fluvial and coastal pollutionduring rainfall events. The Great Olympic sewerage works was completed in 1992,

but the sewer network was still insufficient, inflexible and under conventionalmanagement. At this time the municipality became aware of the need for a newapproach towards the sewer system and its management. This resulted in the councilcreating a new company, CLABSA, which is a public-private partnership tasked withtransforming the drainage system. CLABSA is focused on the planning, control andexploitation of technology to be more effective against flooding and pollution(Salamero et al., 2002).

The main drivers for improvement have been fulfilment of EU directives, increaseddemand on the system, increased environmental awareness and coordination problems

with wastewater treatment plants (WWTP). With this in mind a new AdvancedManagement of Urban Drainage (GADU) approach has been utilised. The mainprinciples of this integrated approach are:

o Having a detailed knowledge of the system;

t ti l l/ l b l t l f 10 t k (Fi 23) 19 i t ti d 36


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automatic local/global control of 10 tanks (Figure 23), 19 pumping stations and 36gates (Figure 24). The system is strictly maintained and uses appropriate controlalgorithms and the extensive SITCO database within SIMO to simulate levels and

flows in the network, as well as CSO spills and their effect on receiving waters.

The Master Drainage Plan also identified a need for a 70% reduction in CSOs.Therefore between 1997 and 2005 a range of interventions were implemented,including:

o 10 x 500,000 m3tanks (Figure 23);

o 1 storage gate and 5 diverting gates (Figure 24);o 25 km of sewers with large dimensions.

In 2002, a pilot RTC scheme was conducted in the Bac the Roda catchment todevelop a methodology for Barcelona-wide implementation (Barro et al., 2002),which was then fully implemented.

During a rainfall event the infrastructure is managed using RTC across a range of

emergency levels, which are summarised in Figure 25. RTC of the detention tanks haspermitted the regulation of 2,700,000 m3of discharges per year (including industrialdischarges), preventing 470 tonne of suspended solids being spilled. This has

needs report: appendix b

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