TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Chapter - 1

INTRODUCTION

1.1 GENERAL

Dam: Dam is a manmade barrier built across a river to hold back river water for safe

retention and storage of water or control the water flow. Dams allow to divert the river flow

into a pipeline, a canal or channel (Fig 1.1). Dams result in substantially raising water levels

in the river over a large area, thus create a storage space. Dams may be of temporary or

permanent nature. Dams may be built by constructing an embankment across the river at

some suitable location. The water body created behind a constructed embankment or dam is

called a manmade lake or reservoir. Dams are built by humans to obtain some economic

benefits.

Natural processes as landslide and rock falling into the river may obstruct the river

flows for some time and create a dam like condition. The earthquake of 2005 resulted in a

debris embankment of more than 200 m width and 70 m height across Karli/Tang Nullah near

Hattian Balla in AJK (Fig. 1.2a). Considering the stability of the debris fill the water

impoundment was used as a tourist point until 2010 when heavy rainfall in the catchment

area caused a huge flood wave leading to failure of dam by overtopping. A recent land slide

caused a large rock mass to form a 2 km long, 124 m deep and 350 m wide fill across Hunza

River with formation of 375+ ft (115 m) deep and 25+ km long Attabad lake (Fig. 1.2b)

disrupting communication network KKH in the area. Effort is underway for planned

demolition of this dam. Wildlife (Beaver) may also create ponds or small dams for their

habitat purposes.

Reservoir: Reservoir is defined the as a man-made lake or fresh water body created or

enlarged by the building of embankment, dams, barriers, or excavation and on which man

exerts major control over the storage and use of the water (Golze 1977, P-619). The

embankment may be constructed on one or more or all four sides of the reservoir. Fig. 1.3

shows a reservoir created at a high location than river to boost operations of a pumped

storage hydropower plant.

Need:

1. River supply usually does not match with the demand at all times/months. Dam’s

storage reservoir is created to match releases with the water demand.

2. Dams are created to substantially raise water level and thus provide working head for

hydropower production or to direct water into off taking canals (e.g. irrigation canal).

0

50

100

150

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Ave

rage

mo

nth

ly

dat

a (T

h.A

F)

KT Dam: Average Supply and Demand Supply

Demand Excess river flows stored

Stored water released to meet demand

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Figure 1.1a: Water reservoir created by Tarbela Dam.

Figure 1.1b: Aerial view of Tarbela Dam’s 65+ km long reservoir (Source: Earth-Google).

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Length of Lake = 2000 Mtr

Average Width = 350 Mtr

Average Depth = 50 Mtr

X-SECTION

KARLI NULLAH LAKE

2.2 KM

202’ 189’ 171’ 149’ 137’ 122’ 110’ 95’ 77’ 57’

44’

100 M

100 M100 M

100 M100 M

100 M100 M

100 M100 M

100 M100 M

BED OF NULLAH

150 M60 m

4’

INLET

DISCHARGE

30’

Figure 1.2a: Natural dam across Kalri Nullah AJK formed by land slide due to earthquake.

Figure 1.2b: Natural dam across Hunza River formed by land slide. A spillway was

excavated to drain the Attabad lake reservoir and planned breaching

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Figure 1.3 : Upper Reservoir of Taum Sauk 450 MW pumped power plant (Reynolds

County, Missouri, on the East Fork of the Black River) made of ridge top 6562 ft long

84 ft high CFRD dike with 10 ft parapet wall. The reservoir dike constructed in

1960’s failed on Dec 14, 2005 due to internal leakage and slope failure. Plant

remained out of use as of Jan 2007. [http://www.ferc.gov/industries/

hydropower/safety/projects/taum-sauk/consult-rpt/sec-2-summ.pdf].

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Purposes

Dams and reservoirs are built to raise water level for storage and safe retention of

large quantity of water. Water is subsequently released to achieve various purposes. Dams

may be constructed to meet one or more purposes as (USBR 2001, P:1-3):

1. Irrigation (e.g. Tarbela and Mangla dams)

2. Hydropower development (e.g. Bunji dam)

3. Domestic, municipal, industrial water supply (e.g. Hub dam, Simly dam)

4. Stock watering

5. Flood control

6. Recreation (picnic, camping, fishing, swimming, kayaking, white water

rafting)

7. Fish and wildlife protection and development, and improvement of river

ecology

8. River water quality / pollution control and management

9. Stream flow regulation for various purposes

10. Navigation

11. Mining (for processing of raw ore or waste materials),

12. Mine tailings dam (to store mine processing waste product)

Multipurpose dams:

Most dams are multi-purpose, serving more than one purpose. Mostly these additional

purposes are achieved as byproduct outcome, e.g., hydropower, recreation, etc. For

multipurpose dams, the storage is allocated and prioritized for different purposes and cost

allocation (Fig. 1.4).

1.2 DAM AND RESERVOIR DEVELOPMENT STRATEGY

Reservoir design can be considered in a broader sense. It is really selected with such

improvements or remedial work as may be considered necessary to assure safe and

satisfactory performance of its intended purpose. Development of a reservoir must assure

structural integrity and adequacy of the reservoirs. The reservoir site is evaluated in terms of

geology, rim stability against slides, water tightness and water holding capability, seismicity,

Storage for

Irrigation and

other uses

Flood detention space Flood surcharge

Free board

Hydro

power

plant

Normal conservation level Max spillway

crest level

Dam crest

Figure 1.4: Multipurpose dam.

Dead storage

Power tunnel

/ irrigation

outlet Dead storage level

River bed profile before

dam construction

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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bank storage, evaporation, sedimentation, land use and mineral resources, right-of-way and

property ownership, relocation of the populace, utilities, and transportation facilities,

historical-cultural and religious monuments, resettlement, etc.

The water stored behind the dam exerts a large water pressure on the dam. A dam

must be able to withstand such high pressures. In addition dam must be safe against failure

due to overtopping, foundation thrust failures, destruction of dam body due to internal

erosion and material failure, foundation uplift, and retain storage contents – practically no

loss of water due to seepage.

Natural or man-made water bodies, albeit large ones, has high aesthetical appeal and

thus attract huge number of visitors for recreation. The reservoir design must include

provisions of recreation facilities as parking area, picnic area, camping area, hiking and

biking trails, nature walk trails, horse trails, rock climbing, enjoying surrounding scenery,

water sports, motel, public services, restrooms, emergency services, indoor shelter areas,

project guided tours, etc. These should be evaluated in terms of need vs luxury and security

concerns for the structure and public.

Reservoir area requires clearing of brush/shrubs/trees from below maximum reservoir

levels for safe use of reservoir surface. Such clearing may be done by cutting/pulling or by

protected fires. In flat side reservoirs large surface area is exposed on reservoir lowering.

Suitable alternatives may be evaluated to make economic use of this area for short time

activities, as farming, sand mining etc.

1.3 CLASSIFICATION OF DAMS

Dams can be classified according to many different features as location, release

pattern, hydraulic design, size, filling and emptying mode, service region, type of materials,

etc.

1.3.1 According To Location

On-Channel: Dam is constructed across the main water feeding river. Examples Tarbela,

Mangla, Simly, Hub dam. Water from other rivers may be diverted to the dam

through feeder channels to increase the water availability, e.g. Kurram Tangi dam.

Off-Channel: Dam is constructed on a channel having much smaller flow. Major storage

water is transferred from a different nearby river. This is done due to non-availability

of suitable/economic dam site on the major flow river. Example Akhori dam.

1.3.2 According to Release Pattern

Storage dam: Water is stored and later released through an outlet for consumptive or non-

consumptive purposes as per requirements. The outflow is controlled as per need.

Recharging dam. There is no outlet provided to release water and all incoming water is

retained. The water infiltrates through the foundation and/or dam body. The main

purpose of the dam is to induce recharge to ground water system in the area. Small

release in d/s channel may be made to allow seepage in the channel bed.

Delay action dam / retarding dam. These dams are used to retard the peak flow of flash

floods. There may or may not be any control over the outflow. For no control over the

outflow the outflow rate varies as function of storage volume / water depth in the

dam. The flood peak is thus considerably attenuated. The outlet capacity is set that

maximum outflow discharge do not exceed the safe capacity of the downstream river

during highest flood. The reservoir empties fully after the flood. For control on

outflow by gates (detention dam) , the flow is released in such a pattern to retain the

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water for long time but there is enough storage available to store next flood event.

These dams are usually meant to reduce flood damages as well as to induce maximum

recharge in the area. One type of such dam is a porous dam built of a porous

embankment, e.g. stone gabions.

Diversion dam These are hydraulic structures with a main purpose to raise water level to

divert flow into the off taking channels / canals/ hydropower pressure tunnels and

penstock of run-of-river hydropower projects. These are preferably called as barrage

or canal head works. The storage created by these is minimal, e.g. Patrind Weir.

Coffer dam: These are small temporary dams built across the river on upstream and

downstream side of the main dam in order to keep the flow away and the working

area dry. The u/s coffer dam causes the flow through the diversion system and d/s

coffer dam prevents the flooding of the working from backwater effects. After

completion of the main dam the u/s coffer dam may be made part of main dam or

abandoned to drown in the reservoir while d/s coffer dam is dismantled and removed.

Tailings dam These dams are constructed away from any river along a topographic slope by

constructing small dikes on three or all four sides to store slurry / waste of mineral

mining and processing facilities. The water evaporates or is evacuated and the solid

contents dry up filling up the storage capacity.

1.3.3 According to Hydraulic Design

Non-Overflow dam: Flow is not allowed over the embankment crest for reasons of dam

safety. (earth, rock) dams.

Overflow dam The dam body is made of strong material as concrete and flow is allowed

over the dam crest Concrete dams

1.32.4 Classification of dams according to Size

Dams may be classified as small, medium or large as under:

Small. USBR defined small dam as one having maximum height < 15 m (50 ft).

Medium: Intermediate sizes 40-70 ft

Large: ICOLD defined large dam as: a dam that follows one or more of following

conditions. (Thomas 1976 P-0)

Dam height > 15 m (50 ft) measured from lowest portion of the general foundation

area to the crest

A dam height 10-15 m but it compiles with at least one of the following condition:

a. crest of dam longer than 500 m

b. capacity of the resulting reservoir more than 1 million m3

c. maximum flood discharge more than 2000 m3/s (70,000 cfs)

d. dam has specially difficult foundation problems

e. dam is of unusual design

Unique: Dams exceeding 100 m are considered as unique. Every aspect of its design and

construction must be treated as a problem specifically related to that particular site.

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1.3.5 According to Filling and Emptying Mode

The storage of a dam may be filled and emptied in short time (one season) or long

time (several seasons). The dams are defined as:

Seasonal: Seasonal dams are filled and then emptied within the same water year (September

to August). Example Tarbela dam. Thus water level in the dam varies from maximum

(normal conservation level) to minimum (dead storage level) in most years. Such

dams have annual releases usually equal or little more than the minimum annual flow.

For very wet or very dry years the reservoir may not reach the extreme levels. The

seasonal dams spread the water stored in wet months over to dry months in the same

year thus provide service for a single season only.

Carry over: Filling and emptying of a carry-over dam reservoir continues over more than

one year (e.g. 2 to 5 years). Example. Hub Dam, Kurram Tangi Dam. Thus water

stored in wet years may be released during subsequent dry years The annual releases

are usually more than minimum annual flow but equal to long term average annual

flow. Carry over dams are applicable where wide variations occur in annual flows.

Carry over dams spread storage during wet years/months over to dry years and

months and thus provide service for multiple seasons.

1.3.6 According to location of service area

Local: The service area of the dam is limited to a single contiguous localized geographic area

located very near the dam. Far located areas and geographic regions do not benefit.

E.g. Kurram Tangi, Simly, Khanpur dams.

Regional: The service area of the dam extends to many widely apart geographic regions

located any distance from the dam. Thus all near and far located areas and geographic

regions get the benefit. The water supply to all areas is possible through a network of

river and canal systems. Exampleas are Tarbela, Diamir-Basha, Kalabagh, Mangla

dams.

1.3.7 According to type of material

A dam can be made of earth, rock, concrete or wood. Dams are classified according to

the materials used as under: (Novak et. al. 2001 P: 11-18, 33)

A. Embankment Dams (Figs. 1.5 to 1.6)

The embankment dams are made by use of natural materials of earth and rock only

and no cementing materials are used. Same or varying materials are used to construct the dam

embankment. There are two main types:

1. Earthfill Dam: These are constructed of selected soils (0.001 ≤ d ≤ 100 mm)

compacted uniformly and intensively in relatively thin layers (20 to 60 cm) and at

controlled optimum moisture content. Compacted natural soils form more than 50%

of the fill Material. Dams may be designed as: Homogeneous, Zoned or with

impermeable core (Figs. 1.5 and 1.6a). Zoned part is made of relatively finer material

that reduces seepage flow, e.g. clay. The fill material is placed as rolled, hydraulic fill

or semi-hydraulic fill.

2. Rockfill dam: Over 50% of fill material be of class ‘rock’ usually a graded rockfill

(0.1 ≤ d ≤ 1000 mm) is filled in bulk or compacted in thin layers by heavy plant.

Some impervious membranes/materials are placed in the interior or on u/s face of the

embankment to stop/reduce seepage through the dam embankment (Fig. 1.6b). Dams

section may be homogeneous, zoned, with impermeable core, or with asphalt or

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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cement concrete face. Zoned part is made of relatively finer material that reduces

seepage flow, e.g. clay. Core is made of clay, concrete, asphalt concrete etc.

Dams made from mix of large proportions of earth and rock materials are called as

Earthfill-rockfill or Earth-rock dams.

Figure 1.5: Earthfill dam. Left-homogeneous dam, right-zoned dam.

B. Concrete Dams

Concrete dams are formed of cement-concrete placed in the dam body. Dam section is

narrow with steeper side slope (Figs. 1.7a,b). Concrete dam section designed such that the

loading produces compression stress only and no tension are induced any where. The

reinforcement is minimum mainly as temperature control. Concrete is placed in two ways: as

conventional plain/reinforced concrete (RC dam) or as roller compacted concrete (RCC

dams). Rubble/random/stone masonry may be used as bulk material in dam section. The

variations of concrete dam include:

1 Gravity dam: Stability due to its mass. Dam straight or slightly curved u/s in plan (no

arch action). The u/s face is vertical or nearly vertical, d/s sloping.

2. Arch dam: Arch dam has considerable u/s plan curvature. U/s and d/s faces are

nearly straight / vertical. Water loads are transferred onto the abutments or valley

sides by arch action. Arch dam is structurally more efficient than concrete gravity

dams (requires only 10-20% concrete). However abutment strength and geologic

stability is critical to the structural integrity and safety of the dam. Multiple arch

dams.

3. Cupola/Dome/Double curvature dam:. U/s & d/s faces curved in plan and profile

section, curved in plan as well/ as arch (Part of a dome or shell structure).

4. Buttress dam: It consists of continuous u/s face (i.e. deck) supported at regular

intervals by d/s buttress or crib. Types include massive buttress, diamond head, round

head with each section separate. Ambursen / flat slab buttress / decked buttress.

5. Hollow gravity: Dam section are made hollow to reduce uplift pressure at d/s side

and smaller total construction materials. (This type falls between gravity and buttress

dams)

C. Timber/steel dam

The bulk of the dam is made of timber braces with timber board facings. Such dams

were mostly constructed by early gold miners in California USA for obtaining river water for

separating gold dust and getting water power; such dams are not practically used any longer.

The face of earthfill or rockfill dams may be also fitted with timber board for seepage control.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.6a: Earthfill embankment dams.

Figure 1.6b: Rockfill embankment dams.

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Figure 1.7a: Concrete dams.

Figure 1.7b: Future Concrete dams.

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1.4 PLANNING AND DESIGN OF DAM

1.4.1 Stages

Any dam project is carried out at following stages

Initial screening based on river profile and topographic maps.

Reconnaissance plan-uses only any available data

Pre-feasibility plan-little exploration and additional field data

Feasibility plan-Extensive exploration and additional field data

Design stage: – point tests/surveys to finalize design

At each succeeding stage, the plan is firmed up with more precise details, dimensions and

analysis; More data is used at each successive stage. The design stage ends up with drawings

appropriate for construction activities. Still further details/revision continues well during the

construction of the dam as new information is gathered or some already available information

is found to be incorrect and not valid.

1.4.2 Data Required

Large amount of data is required for planning/designing of dams (Golze, 1977 P. 47-50).

These include as:

1. Location & vicinity map

2. Topographic maps/aerial photographs of dam site

3. Elevation surveys/triangulation + bench mark

4. Transportation map (road, rail, air)

5. Geological / rock formations data of dam site

6. Seismic/tectonic activity map

7. Climatic data (P, T, ET, wind, sunshine)

8. Stream flow data (daily average flows)

9. Sediment data

10. Flood data (instantaneous peak flow rates, time to peak, base time, flood duration,

flood volumes, flow hydrograph, etc) of all or major floods

11. Water rights

12. Demographic/land ownership/housing data for the reservoir area, resttlement

13. River environment/ecology (u/s, at site, d/s) (fish, w/life, birds, flora, fauna,

vegetation)

14. Project water requirement

15. Power requirements & national grid / transmission lines

16. River hydrographic data (bed levels, flood levels, cross section, bank/valley

levels)

17. River stage-discharge data (u/s, tail water)

18. Groundwater table data in the vicinity, u/s and d/s area

19. Public recreation need

20. Land evaluation

21. Public/Private buildings

22. Availability of construction materials

23. Geo-political economic data

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1.4.3 The Planning/Design Team

Dam planning/design is a multi-task activity; various tasks are as:

(1). Site selection, (2). topographic surveys, (3). water availability assessment, (4). sizing and

layout, (5). geologic surveys and construction materials investigations, (6). geologic

evaluation of foundation, rim, abutment and pond area, (7).dam section design, (8). dam

seepage and stability analysis, (9). Diversion arrangements details (diversion tunnel, coffer

dam), (10). floods and spillways, (11). hydropower works, (12). irrigation outlets and

irrigation system design, (13). Reservoir sedimentation, (14). Reservoir operation studies,

(15). Material quantities and costing, (16). Environmental studies, (17). Land acquisition and

replacement, etc.

Thus planning and design of dam is a multi-disciplinary task and require teamwork of

following disciplines:

1. Project Manager (for overall project control)

2. Water resources engineer (for project design and water supply demand studies)

3. Layout planner (for alternate locations and/or layouts)

4. Surveyors (for plan and topographic surveys of reservoir area)

5. Hydrology + meteorology (to assess water availability, and floods)

6. Engineering geologist, Geophysist/Siesmologist, Geophysical exploration

specialist / Drillers (for foundation and abutment exploration)

7. Geo-technical engineers (for foundation, embankment and cut slope design)

8. Hydraulic engineer (for hydraulic design of outlets, spillway, energy dissipation)

9. Structural engineer (for structural design of outlets, spillway. Powerhouse, energy

dissipation)

10. Mechanical engineer (for design of controls, gates, valves, hoists, )

11. Hydropower engineer (for layout and design of hydropower units)

12. Electrical engineer (for design of electric power controls and transmission)

13. Instrumentation engineer (for monitoring instrument design)

14. Telecommunication engineer (to design workplace and office communication)

15. Environmental engineer, Environmental scientists (to study environmental

impacts of the project on fish, wild life, flora, fauna, etc and needed mitigation

measures to maintain healthy and conducive environment for on-site and off-site)

16. Infrastructure/road/municipal engineer / Civil engineer (for layout and design of

office space, workshops, access road network, contractor camp, workmen

housing, security system, water supply, solid liquid waste disposal)

17. Quantity Surveyor / Costing engineer (to quantify construction material volumes,

material unit costs, total project costs

18. Construction planner / manager (to design construction activity chart, time and

cost scheduling, critical time analysis)

19. Economists (to determine project financial and economic viability [B/C ratio,

NPW, IRR], project cost repayment capacity and schedule

20. For associated irrigation development more professionals as Irrigation engineer,

Irrigation agronomist, Soil expert will be required.

1.5 DAM SITE SELECTION

The purpose of a dam is to retain and store large quantities of water in a safe way.

Many considerations are analyzed. Most desirable condition is that dam project can provide

largest storage volume with smallest dam size (in terms of dam length and height) for dams

for irrigation purposes whereas small storage volume is required for run-of-river hydropower

projects. The dam storage space may be viewed considering river valley geometry u/s of

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proposed location in terms of river bed profile (steep, gentle or moderate, and flat - Fig. 1.8)

and river cross section (wide, narrow, and gorge – Fig. 1.9) and river valley depth below

adjacent mountains/rocks (deep, medium, shallow). River with flat bed profile and wide cross

section will provide large storage volumes and are thus most desirable for irrigation dams. On

the contrary steep river bed profile with cross section as narrow to gorge is good for run-of-

river hydropower dams which normally need small storage volumes. Deep river valleys

provide large storage volumes and shallow valleys provide small storage volumes.

A dam can be built anywhere if you can spend enough money. However preferred site

have following characteristics which lead to lower project costs. Thus alternate dam sites

locations are evaluated for most cost effective choice. Many times trade-off and compromises

are made to select a dam site.

1. Small river channel width with steep side gorge: short dam crest length, leads to

large storage for small dam length

2. A wide and flat sloping valley upstream of the dam site (for storage dams) and

narrow and steeply sloping valley for hydropower dams.

3. River channel and valley has very flat slopes u/s of dam site (leads to large storage

for small dam heights).

Dam

Steep

Gentle

Flat

Max water level

Figure 1.8: River bed profile

Wide Narrow Gorge

Figure 1.9: River valley cross section and depth

Max water level

River

Shallow

Medium

Deep

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4. Deep valleys - Deep reservoir possible – require less area and lesser land costs,

less surface evaporation

5. Enough water flow/yield available to meet requirements/demand

6. High sediment load tributaries are excluded

7. Geology favorable for foundation (foundation can be designed at any site, but it

increases costs), competent hard rock is most suitable.

8. Abutments are water tight, and reservoir rim allow minimum percolation and

seepage losses.

9. Small river sediment rate (longer dam life); this depend on river morphology and

catchment characteristics. More sediment load requires large dead storage space.

10. Land use of reservoir area is minimal – lower economic values mean smaller

resettlement issues and lower compensations.

11. Reservoir area not very sensitive to environment (wild life parks, endangered

species, historical places, monuments etc).

12. No seismic and tectonic activities or active faults in and near the site.

13. Socio-political stability (no unstable gestures) (Gomal-Zam, Mirani, Kurram

Tangi dams), Diamer-Basha vs Kalabagh dams.

14. Reservoir and dam area less populated

15. Site have adequate stream flow record

16. Site is easily accessible; approach road is present or can be developed easily.

17. Construction material available nearby easily

18. Site near load center (demand area) for water+ power

19. No mineral resources in reservoir area (present or future)

20. Site allows a deep reservoir & small surface area (less land costs and small

evaporation losses).

21. Transportation system (air, rail, road) available to reach site and carry

construction materials and machinery.

22. Existing infrastructure, e.g. highway, least affected, e.g. KKH and Diamir Bhasha

dam.

1.6 DAM COMPONENTS

Elements of a typical dam include (Figs. 1.10 and 1.11):

1.6.1 Main Dam

This is the main structure built across the river. The height of a dam depends upon

desired storage capacity and the site conditions. The crest length of the dam depends upon

topography at the dam site. The dam may be built of many different materials (Figs. 1.6 and

1.7). The stored water is released from the dam as per requirements.

1.6.2 Flanks/Abutment:

The rock mass on right and left banks of the river constitute abutments. Dam is joined

with and supported by the abutments. In addition outlet tunnels, diversion tunnel, spillways

are also placed in the flanks. The geology of the abutments has to be strong enough to enable

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placing various structural components without any risk. In addition abutments need to be of

competent rock of lowest permeability without any structural defects.

1.6.3 Saddle Dam:

The reservoir is usually formed by the main dam on one side and low/high hills on all

other sides of the reservoir. In most cases the elevation of the hills along the rim of the dam is

much higher than the reservoir maximum water level. In some other cases elevations of

surrounding hills along a part of the rim/periphery of the reservoir is not high enough over a

small section to completely contain the stored water and a saddle (low level place) is formed.

Water can flow out through the saddle. A small embankment is then constructed at this

low/saddle point to seal off the reservoir rim and is called as saddle dam. Example: Sukian

dam and Jari dam for Mangla Dam project.

1.6.4 Diversion Channel/Tunnel

This is water conveyance system from upstream of u/s coffer dam to downstream of

d/s coffer dam. These channel or tunnel are constructed prior to dam construction such that

river flow is passed around and away from the dam site through the diversion tunnels and that

than dam site remain dry and accessible to construction at all time. The capacity of diversion

structure is set such that most probable floods likely to occur during the construction period

can be passed over without danger of overtopping of cofferdam and inundation of

construction area. Necessary arrangements are made at d/s end for energy dissipation. These

tunnels may be abandoned (plugged – Simly dam) after project completion or converted to

irrigation / power / desilting tunnels. Diversion tunnel may not be provided (Mirani dam) and

u/s coffer dam.

1.6.5 Cofferdam

These are small temporary dams built u/s and d/s of the dam site to make the

construction area dry and workable. The u/s cofferdam causes water to flow through the

diversion tunnel and the d/s cofferdam prevents backwater level to inundate the construction

area. Coffer dam may be dovetailed in u/s part of dam (Mangla) or abandoned. Material used

earth, rock, concrete etc. Arrangemnet are required for control of seepage across the coffer

dam.

1.6.6 Spillway

This is a water release/conveyance structure to pass the large flood volumes safely

across the dam without danger of overtopping of the dam crest. There would be one or more

spillways usually at different levels (Service, additional, emergency). The lower spillway is

used to release often occurring flood and regular inflows and is called as service spillway. It

has usually more elaborate arrangements and may be free flowing or gated. The auxiliary or

emergency spillway is set at or above normal conservation level and has fewer arrangements

and is usually free flowing. This is used only during flood events of extra-ordinary nature.

Fuse plug, rubber dam etc may be used to delay water release and possible additional storage

at the reservoir.

The spillway may be an integral part of the main dam (mostly for concrete dams) or be a

separate structure in the dam abutments.

1.6.7 Outlet Works

(a) Intake Structure / Tower: This is a structure to admit and control flow of water into the

irrigation/power outlets. It would be a tower or inlet flush with reservoir side walls. Gates

may be provided at u/s, intermediate or d/s end of the outlet tunnel. Necessary provision is

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

17

made to keep the intake operation for long after sedimentation by having multiple water entry

levels particularly for domestic supply purposes. Multi level inlet openings may be used.

(b) Irrigation/Power Outlet Tunnel: This is a large water conveyance structure to release

water to irrigation network and/or powerhouse turbines. The outlet is in the form of a tunnel

dug or formed through the abutment / flank for earth / rockfill dams or through the dam body

for a concrete dam. At the u/s end an intake is provided along with gates, trash rack. The

tunnel design must eliminate risk of cavitation and/or aeration. Gates may be placed at u/s,

d/s or intermediate location. The power tunnel is transitioned into surge chamber,

penstock/scroll case etc. Energy dissipation structure may be provided at d/s end, if needed.

Irrigation outlet may release into a canal or into the river if demand site is at distance from

the dam. The intake level of the tunnel is kept below or at the dead storage level. Air vent is

provided to minimize cavitation. Water cushon for vortex control are also provided.

(c) Low Level Outlet: A low outlet tunnel may be provided to flush sediments, draw water

from below dead storage level under very drought condition, emptying of reservoir in

emergencies, draw water during repair of outlet tunnel/gates, etc. The intake level is kept

much lower than the intake level main irrigation tunnel. May discharge into stilling basin for

spillways/outlet works or as a separate energy dissipation structure provided.

Figure 1.10: Dam components (http://www.dnr.state.wi.us/ORG/WATER/WM/dsfm/dams/gallery.html)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

18

Figure 1.11: Dam layout showing main dam, saddle dam, u/s and d/s coffer dams, spillway

and stilling basin, diversion tunnel(s), power tunnel, power house and irrigation canal.

550

500 450

500

450

400 500

400

PH 450

Saddle dam

u/s coffer dam

d/s coffer dam

Maindam Spillway

Diversion tunnel Outlet

Reservoir limits

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

19

1.6.8 Seepage Control and Drainage System

Dams are designed to store water with least seepage through the dam embankment

and the foundation but seepage do occur. The drainage/seepage water also causes tremendous

uplift pressure particularly at d/s half of the dam base. Features are included in the dam

design to minimize seepage through the foundation and through the dam embankment and

uplift pressure. Arrangements are provided for safe exit of unobstructed seepage. These

include: Cutoff wall, Sheet piles, Slurry trench, Grout Certain, U/s Blanket, Pressure relief /

Drainage Wells, Drainage gallery, Blanket Drain, Chimney Drain, Toe Drain, etc.

1.6.8 Preliminary Works

This includes civil works, infrastructures, buildings required to be provided before

start of construction of main dam work. These include offices, staff housing, community

buildings, water supply, approach road, client/consultant/contractor camp, labor camp,

security arrangements, rest house, rail sidings, air strip, helipad, etc.

1.6.9 Hydropower Development

(a) Powerhouse: Building to house turbine, generators, mechanical workshop, valves, draft

tube, office, control room, visitor area, up transformer, etc for hydropower generation.

(b) Penstock: This is a large diameter pressure pipe used to deliver water to turbines.

(c) Surge chamber. To contain water hammer surge on plant load rejection / sudden shut-

down.

(d) Switchyard: This is an area to install electrical equipment to change low to high tension

power supply for further transmission.

Other features include power channel, head race channel, tail race channel, draft tube etc.

1.6.10 Slope protection/Riprap

Stone is placed on u/s & d/s dam slopes for protection against damage due to wave

action, rain water, burrowing animals. Parapet wall may be used to protect dam top against

sudden waves generated by strong winds, tsunami, etc.

1.6.11 Dam Instrumentation

Various gages/instruments are installed in the dam body, foundations, spillway to

monitor settlement, movement, stresses, pore water/uplift pressure, earthquake.

1.6.12 Stilling Basin

To dissipate excess energy of diversion tunnel, low level outlet, irrigation tunnel,

spillway, etc.

1.6.13 Gallery/Shafts

These are provided in the dam body for access to interior of concrete dam body.

These are horizontal, vertical (with round stair ways), sloping.

1.6.14: Operational buildings

These are buildings required for operation of the dam and works. These include

Office buildings, Rest House, Security buildings, Staff residences and other community

buildings, gate control room.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

20

1.6.15: Temporary works:

These are installations required for temporary use and are removed after project

completion. These include contractor’s camp, material processing, handling and stock area,

machine room, casting yard, steel fabrication, labor camp, etc.

1.7 MERITS AND DEMERITS OF DAMS

1.7.1 Embankment Dam

a Merits (Novak et al. 2001 P-14)

1. Suitable to type of sites in wide valleys and relatively steep sided gorges alike.

2. Adoptable to a broad range of foundation conditions-from competent rock to soft

and compressible or relatively pervious soil foundation.

3. Use of natural materials at smaller cost thus no need to import or transport large

quantities of processed materials or cement to the side.

4. Subject to the design criteria, embankment dams are extremely flexible to

accommodate different fill materials (rock, earth) if suitably zoned internally.

5. Construction process highly mechanized and continuous (less human handling as

form work, curing time)

6. If properly designed, dam can safely accommodate appreciable degree of

settlement-deformation without risk of serious cracking and possible failure.

Embankment dams withstand earthquake better. However the foundation of these

dams, if deep and of unconsolidated origin, is more liable to settlement and failure

by earthquake (liquification).

b Demerits

Inherent greater susceptibility to damage or destruction due to over topping

(require adequate flood relief and separate spillway).

Vulnerable to concealed leakage and internal piping/erosion in dam or foundation.

c. Limitations

Spillway and outlet are usually separate from main dam.

1.7.2 Concrete/Masonry Dams

a Concrete Dam Merits (Novak et al. 2001 P-17)

1. Concrete dams, except arch and cupola, are suitable to site topography of wide or

narrow valley alike, provided that a competent rock foundation is present at

moderate depths (< 5 m) (arch best for narrow section)

2. Concrete dams are not sensitive to overtopping under extreme flood conditions.

3. All concrete dams can accommodate a crest spillway, if necessary, over the entire

dam length, provided that steps are taken to control d/s erosion and possible

undermining of the dam. Thus cost of separate spillway is avoided.

4. Outlet pipe works, valves and ancillary works are readily and safely housed in

chambers or galleries within the dam. Power house can be placed at d/s toe of

dam.

5. Has high inherent ability to withstand seismic disturbances.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

21

6. Cupola dam is extremely strong and efficient structure for a narrow valley with

competent abutments.

b Demerits

1. Concrete dams require sound and stable rock foundations.

2. These require processed natural materials of suitable quality and quantity for

aggregate and importation to site and storage of bulk cement and other materials.

3. Traditional mass concrete construction is slow, labor intensive and discontinuous,

and require adequate skill for formwork, concreting etc.

4. Cost per unit of concrete dam much higher than embankment fill. Smaller

quantities seldom counter balance for dams of given height.

1.8 DAM FOCUS POINTS (Novak et al. 2001 P 10-11)

Dams have following focus points and thus differ from other major civil engineering

structures.

1. Every dam, large or small, is quite unique; foundation geology, material

characteristics, catchment yield and flood hydrology are each site specific.

2. Dams are required to function at or close to their design loadings for extended

periods.

3. Dams do not have a structural life span, components must be designed for long

life). Dams may have notional life for accounting/economic purposes, or a

functional life span dictated by the reservoir sedimentation. Dams may be

decommissioned at the end of their useful life; this may lead to dam demolition.

4. Majority of dams are of earth fill made from a range of natural soils, and are least

consistent of construction materials.

5. Dam engineering draws together a range of disciplines to a quite unique degree

(hydrology, hydraulics, geology, geotechnical, structure etc).

6. FIRST PLAN: All type of dams may be considered at the site, thus plan

alternative design until discarded due to technical, financial or environmental

reasons.

7. Dam engineering is critically dependent upon the application of informed

engineering judgment. Some compromise tradeoffs are always considered.

1.9: ELEVATION-AREA-VOLUME RELATIONSHIP

The elevation-volume-area relationship for a reservoir/dam describes the variations of

volume and surface area with elevation/height. This relationship is determined from elevation

contour map of the reservoir area. The elevation is determined by topographic survey at grid

or random locations (grid spacing varies with level of investigation from 200 m for pre-

feasibility study to 50 m or less for feasibility study). Wide contours indicate a gently sloping

flat valley area and closed spaced contours indicate steeply sloping cliff sides. Contours are

drawn at an interval of 5 to 10 ft (Fig. 1.12). Surface area is measured for each contour line.

The incremental volume between two consecutive contours is determined by trapezoidal

formula as:

V = (A1+A2)/2×h (1.1)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

22

where A1 and A2 is plan area of the two consecutive contours with h contour interval. Total

volume at any elevation is obtained by adding successive incremental area as VH = H V.

Table 1.1 below show calculations for elevation-volume-area relationship. The reservoir

surface area and volume is related as (H = Elevation – datum):

Vol. = H

0

dH Area and Area = dV/dH, (1.2)

The data points are plotted with volume or area on x-axis and elevation on y-axis (volume on

primary x-axis, and area on secondary x-axis) (Fig. 1.13).

Equations may be developed (usually a power function) to find elevation for a given storage

or area as

El = A (Vol)B + datum and El = C (Area)

D + datum

where El is elevation, Vol is storage volume, Area is reservoir surface area, and A, B, C, D

are curve fitting parameters.

Table 1.1 : Elevation-Area-Volume Relationship for a Dam.

Map Scale: 1 inch = 5000 ft; 1 sq in = 5000

2 = 25,000,000 sq ft = 1 sq in = 25,000,000 / 43,560 = 573.92 Acres

Selected datum (ft amsl) =1800

Elevation Height above datum

Map area Plan Area Incremental volume

Total storage capacity

(ft amsl) (ft) (sq. in) (Acres) (AF) Acre Feet ThAF

1805 5 0.00 0 0 0 0

1850 50 0.49 281 4,993 5,043 5

1900 100 1.88 1,079 34,005 39,048 39

1950 150 4.11 2,359 85,945 124,993 125

2000 200 7.17 4,115 161,846 286,838 287

2050 250 11.03 6,330 261,134 547,972 548

2100 300 15.69 9,005 383,379 931,352 931

2150 350 21.14 12,133 528,438 1,459,789 1,460

Example. For Kurram Tangi dam the elevation-storage-area relation are described as:

(volume in AF, elevation is ft amsl, and area is in acres and 1805 is datum) (Figs. 1.14 to

1.17).

El = 2.6905 × (Vol)0.3432

+ 1805

El = 2.5821 × (Area)0.5226

+ 1805

For some cases more than one equation may be needed to describe the data for different

ranges. Inverse equations may be derived to find volume or area corresponding to any

elevation, e.g. for Kurram Tangi dam elevation-area-volume dam is described as (Volume in

AF, Elevation in ft amsl, Area in acres and Datum = 1805 ft amsl..

Vol.= 0.05595 (Elevation - Datum)2.913

Area = 0.163 (Elevation ft - Datum)1.9132

Equation form of the elevation-area-volume relationship may be useful for various purposes,

e.g. reservoir simulations, flood routing for spillway design and diversion tunnel design.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

23

Figure 1.13: Kurram Tangi Dam: Elevation-Volume-Surface Area Curves.

0

5

39

125

287

548

931

1,460

0.05

0.28

1.08

2.36

4.12

6.33

9.00

12.13

1800

1825

1850

1875

1900

1925

1950

1975

2000

2025

2050

2075

2100

2125

2150

2175

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1800

1825

1850

1875

1900

1925

1950

1975

2000

2025

2050

2075

2100

2125

2150

2175

0 200 400 600 800 1,000 1,200 1,400 1,600

Ele

va

tio

n (

ft)

Area (Thousand Acres)

Ele

va

tio

n (

ft)

Capacity (Th.Acre-ft)

KURRAM TANGI DAM: Elevation-Capacity-Area Curves

Reservoir Capacity

Reservoir Surface Area

N

2100 ft

2050

ft 2000 ft

1950 ft

Kurram Tangi Dam

2150 ft

Figure 1.12: Topographic surface contours of Kurram Tangi

Dam.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

24

1.10 DAM HEIGHT

The height of any dam above the lowest level in the river channel is determined from

(i) the gross storage (live storage + dead storage) capacity of the dam, (ii) the space required

to pass maximum design flood over the spillway (called flood surcharge), (iii) the wave

height generated from extreme winds, (iv) the wave runup over the upstream sloping face due

to wind gusts and (v) the free board. The reservoir level corresponding to normal reservoir

storage is called as normal conservation level NCL and is determined from the elevation-

volume relationship of the dam. Referring to Figs 1.13, the normal conservation level is

determined as 2076.2 for gross storage capacity of 0.716 MAF. The wave height and wave

runup is determined from reservoir area, depth and prevailing wind speeds in the vicinity of

the dam. Free board of 5 to 10 ft is customary provided depending upon the reservoir

importance and other factors.

For Gross storage = 0.716 MAF (Live storage = 0.55 as determined from mass curve /

reservoir operation studies, and dead storage = 0.166 MAF as determined from sedimentation

analysis), the required dam height is worked as:

Minimum River bed level at dam site = 1805.0 ft amsl

Normal conservation level for 0.716 MAF = 2.6905×(716000)0.3432

+1805 = 2076 ft amsl

Maximum reservoir depth = 2076-1805 = 271 ft

Flood surcharge (from PMF routing) = 6.5 ft

Wave height e.g. = 3.5 ft

Wave runup e.g. = 4.0 ft

Free board e.g. = 10 ft

Total dam height = 271 + 6.5 + 3.5 + 4.0 + 10.0 = 295.0 ft

Dam crest level = 1805.0 + 295.0 = 2100.0 ft

1.11 DAM LAYOUT

Dam embankment

Once the site of a dam is selected, the layout of dam embankment is carried out. The

outline of dam is done on a contour map of potential dam location. Following steps are taken

(Fig. 1.18).

Earthfill-Rockfill dam:

Data: Dam crest level = 2100 ft, u/s face slope = 3.5:1 (H:V), d/s face slope = 3.0:1; contour

interval = 50 ft, river bed level = 1805 ft

Crest:

1. Locate the centerline of dam crest by connecting two points on 2100 ft contour line

along right and left abutments such that the dam has smallest crest length. The

geologic makeup of the foundations and abutments is also considered. Measure the

crest length.

2. Mark the crest width (e.g. 30 ft) parallel to the selected centerline.

3. Mark chainage along the dam crest with 0+00 mark at one of abutments, e.g. right

abutment. Determine the dam crest length.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

25

Figure 1.14: Elevation-Surface Area curve fit to data.

Figure 1.15: Kurram Tangi Dam: Elevation-volume curve fit to data.

52

281

1,079

2,359

4,115

6,330

9,005

12,133

y = 2.582141x0.522649 R² = 0.999916

0

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000

Ele

vati

on

Ft

+ 1

800

Surface Area (Acres)

KTD: Elevation vs Reservoir Surface Area Curve

20

50

100

150

200

250

300

350

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

0 200 400 600 800 1,000 1,200 1,400 1,600

Ele

vati

on

Ft

+1800

Volume (ThAF)

KTD: Elevation vs Reservoir Capacity Curve

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

26

Figure 1.16: Kurram Tangi Dam. Surface area vs. elevation curve.

Figure 1.17: Kurram Tangi Dam: Volume vs. elevation curve.

0 5 39

125

287

548

931

1,460

0

200

400

600

800

1,000

1,200

1,400

1,600

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

Vo

lum

e (T

hA

F)

Elevation (1800+ft)

KTD Elevation vs Capacity Curve

52 281

1,079

2,359

4,115

6,330

9,005

12,133

y = 0.162962x1.913170 R² = 0.999916

-

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

12,000

13,000

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

Su

rface A

rea (

Acre

s)

Elevation (1800 +ft)

KTD Elevation vs Area Curve

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

27

U/s face:

4. Determine the horizontal distance corresponding to 50 ft vertical height for u/s face (

= 50 x 3.5 = 175 ft). [3.5 :1 is slope of u/s face]

5. Mark a line A-A’ on u/s face parallel to crest edge spaced 175 ft apart between 2nd

contour line of 2050 ft.

6. Mark lines B-B’, C-C’, D-D’, E-E’ 175 ft apart between other contour lines of 2000,

1950, 1900, 1850 ft, respectively.

7. Mark location of point F of lowest elevation in the river channel.

8. Connect points A-B-C-D-E-F-E’-D’-C’-B’-A’ with a smooth line and connect the

outline with crest edge on u/s face. This defines the dam outline or footprint along u/s

sloping face.

D/s face:

9. Determine the horizontal distance corresponding to 50 ft vertical height for d/s face (=

50 x 3.0 = 150 ft). [3:1 is slope of d/s face]

10. Mark a line G-G’ on d/s face parallel to crest edge spaced 150 ft apart between 2nd

contour line of 2050 ft.

11. Mark lines H-H’, I-I’, J-J’, K-K’ 150 ft apart between other contour lines of 2000,

1950, 1900, 1850 ft, respectively.

12. Locate point L of lowest elevation in river channel on d/s side.

13. Connect points G-H-I-J-K-L-K’-J’-I’-H’-G’ with smooth line and connect this with

crest edge on d/s side. This defines the dam outline or footprint along d/s sloping face.

Crest length, Longitudinal Section and Cross section

14. Draw longitudinal section (L-section) along centerline of dam crest. This will provide

valley profile between the river’s left and right abutments (Fig. 1.19).

15. Draw dam cross section at maximum depth (section F-L at Ch 7+45 in Fig. 1.19), and

also at other chainage, e.g. at every 200 ft apart (Fig. 1.19).

Concrete gravity dam:

The layout of concrete gravity dam is similar to earthfill dams with the exception that

u/s and d/s face slopes are very small (u/s ~ 1 H:10 V, d/s ~ 0.7 H:1 V)

Dam appurtenants

The layout of dam appurtenants (spillway, outlet, diversion tunnel, power house, etc)

is determined such that space requirement of all dam components is adequately met. Few

trials may be needed to finalize the layout of dam embankment and dam appurtenants.

Figs 1.20 to 1.23 describe the alternate layouts for Kurram Tangi dam for dam

embankment and dam appurtenants.

1.12 DAM ENVIRONMENTAL IMPACTS

Construction of dams significantly alters the river flow regime. The flow in flood

season is considerably reduced while the flow in other months is increased. The changed flow

pattern affects the ecology and echo system of the river d/s reaches. The dam construction

affects the migration of cold-water fish for their annual spawning voyage to u/s cold-water

regions. However the dam reservoir provides an excellent place for supervised fish

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

28

development. The river may have cropped area which is seasonally flooded by the river flood

flows (sailaba area). Construction of dam may lower the flood flows thus the sailaba area

need to be irrigated by alternative means. Affected area adjacent to the dam may be provided

supplemental canal or tubewell irrigation facilities. Waterlogging and high watertable may

appear in some places above or below the dam site.

The sediment carried by the flood water get trapped in the dam and thus a small amount

of sediments enters the d/s reach of the rivers. The imbalance in the sediment flow combined

with educed flood flows causes a aggradations of the river bed. This slowly lead to raising of

the flood levels in the affected river reach requiring a constant raising of flood dikes and

spurs. The sediment reduction due to dams leads to erosion/degradation of the river delta at

the entrance to the ocean. Thus erosion of coastal areas is negatively affected by the

construction of dams.

It is required that environmental impacts of dam may be evaluated independently and

necessary mitigation measures may be taken to mitigate and minimize the adverse

environmental impacts.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.18: Topographic surface contours at a dam and layout of dam outline.

2050

2000 1

950 1900

1850

2100

2100

2050

2000

1950

1900 1850

Dam Crest;

El = 2100 ft

RIV

ER

DOWNSTREAM

SLOPING FACE

UPSTREAM

SLOPING FACE AA

AB

AC

AD

AE

AA’

AB’

AC’

AD’

AE’

AG

AH

AI

AG’

AH’

AI’

AJ AJ’

AK AK’

AL

AF

SLOPE: u/s = 3.5 H:1 V; d/s = 3.0 H:1 V; SCALE = 1:5000.

Ch 1

+0

0

2+00 4+00 6+00 8+00 10+00 12+00 14+00

Crest

length =

1650 ft

175 ft

175 ft

175 ft

175 ft

50×3.5=175 ft

30 ft

150 ft

50×3.0 = 150 ft

150 ft

150 ft

150 ft

SHORE LINE

Contour interval

Δh = 50 ft

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

30

Dam section for concrete dam

Dam section for earthfill dam

Dam Crest; El = 2100 Ft, Length = 1650 ft

Chainage (ft) 2+

00

4+

00

6+

00

8+

00

10+

00

12+

00

14+

00

0+

00

16+

00

1800

1900

2000

2100 E

levat

ion (

ft)

(a) Longitudinal section

Dam crest: El = 2100 ft, width = 30 ft

Normal conservation level = 2081.6 ft

U/s slope =

1 V:3.5 H

D/s slope =

1 V:3.0 H

River level = 1805 ft

885 ft 1032 ft

(b): Dam maximum cross section at F-L Ch 7+45 ft.

295 ft

1947 ft

Dam crest: El = 2100 ft

River level = 1805 ft

675 ft 787 ft

(c): Dam X-section at Ch 4+00 ft.

225 ft

1492 ft

Valley El = 1875-1950 ft

225 ft

El = 1875 ft El = 1875 ft

Dam crest: El = 2100 ft

River level = 1805 ft

765 ft 578 ft

(d): Dam X-section at Ch 12+00 ft.

255 ft

1373 ft

El = 1845

El = 1935 ft 165 ft

Dam crest: El = 2100 ft

420 ft 368 ft

(e): Dam X-section at Ch 14+00 ft.

140 ft

818 ft

El = 1960 ft El = 1995 ft 105 ft

Figure 1.19: Longitudinal and cross section of dam of Fig. 1.18. Scale: 1:5000

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

31

Figure 1.20: Contour map of dam area of Kurram Tangi Dam site.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

32

Figure 1.21: Dam embankment layout of Kurram Tangi Dam.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

33

Figure 1.22: Layout plan of concrete face rockfill dam (CFRD) embankment and

appurtenances for Kurram Tangi Dam.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

34

Figure 1.23: Layout plan of concrete gravity dam embankment and appurtenances for

Kurram Tangi Dam.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

35

1.13 RESETTLEMENT

The construction of dam requires large land area to be occupied by dam embankment,

spillway channel, outlet canals, hydropower plant, offices, approach roads, housing facilities,

etc. In addition the reservoir occupies very large surface area in many square kilometers. The

area to be occupied by a dam and reservoir has to be possessed before the construction of the

dam. The affected area may be under mix of private and public ownership. The area may be

partly or wholly used for various productive purposes as cropping, grazing, rock quarrying,

public entertainment, parks, residential, commercial or industrial purposes, etc. Most of dam

sites are usually remote to present urban and industrial centers; thus a significant part of the

affected area may be barren and unproductive.

Construction of dam will deprive the current occupants of the area from productive

benefits. Nevertheless some inhabitants occupying the river banks and nearby villages will be

needed to be moved out of the area and resettled. The affected persons will not only loose

their residential houses but most often their means of livelihood (agriculture, small to

medium business etc.) In addition the dam and reservoir may inundate some places of social-

religion nature. Some transportation corridors (rail lines, highway, and other roads) may get

submerged. Thus dam project must include a plan to resettle the affected persons to new

places, restoring their economic livelihood, etc which is socio-politically acceptable to the

affected population groups. The affected persons may be provided compensation in the form

of cash, kind (equivalent housing and business units in some nearby areas). It is also

important to ensure the social and cultural harmony and adjustment of the people moving to

new locations.

The transportation corridors have to be moved to new locations above and away from

the dam and reservoirs. The religious and social/cultural monuments and places must be

planned to be protected by flood dikes, by moving to higher and safer levels, etc. Else the

affected persons will react very strongly to the dam project, jeopardizing the whole project.

Monuments of lesser importance may not be protected due to the large numbers. Various

socio-cultural-political groups must be approached, contacted and satisfied to come with

suitable resettlement plans, which is acceptable to both the affected persons and the dam

owners.

Fig. Dam failure.

1.14 DAMS IN PAKISTAN

There are numerous small, medium and large sized dams in Pakistan with main purposes for

irrigation, hydropower generation, municipal water supply. These also provided recreation

opportunity, but now have been closed due to present security concerns. These dams are:

Warsak dam, Rawal dam, Mangla dam, Tarbela dam, Chashma reservoir, Hub dam, Simly

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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dam, Khanpur dam, Satpara dam, Mirani dam. In addition there are more than 50 small dams

owned by provincial Irrigation departments. Figs. 1.24 to 1.30 show features of few dams.

Region wise list of dams is as under:

Azad Kashmir

Mangla Dam

Balochistan

1. Akra Kaur Dam

2. Burj Aziz Khan Dam

3. Garuk Dam (planned)

4. Hingol Dam (planned)

5. Hub Dam

6. Mirani Dam

7. Naulong Dam (under construction)

8. Pelar Dam (planned)

9. Sabakzai Dam

10. Saindak dam

11. Shakidor Dam

12. Sukleji Dam (planned)

13. Wali Tangi Dam

14. Winder Dam (planned)

Federally Administered Tribal Areas

1. Bara Dam (planned)

2. Gomal Zam Dam (nearing completion)

3. Kurram Tangi Dam (planned)

4. Munda Dam (under construction)

Gilgit–Baltistan

1. Bunji Dam (planned)

2. Diamer-Bhasha Dam (under construction)

3. Satpara Dam (nearing completion)

Islamabad Capital Territory

1. Rawal Dam

2. Simly Dam

Khyber Pakhtunkhwa

1. Darmalak Dam (under construction)

2. Jabba Khattak Dam (under construction)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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3. Karak Dam (under construction)

4. Khair Bara Dam (under construction)

5. Khanpur Dam

6. Lawaghar Dam (under construction)

7. Karak Dam (under construction)

8. Palai Dam (under construction)

9. Tanda Dam (Ramsar Site)

10. Tarbela Dam

11. Warsak Dam

Punjab

1. Akhori Dam (planned)

2. Dhrabi Dam

3. Dohngi Dam

4. Ghabir Dam (under construction)

5. Kalabagh Dam (planned)

6. Khai Dam

7. Chiniot dam (planned)

Sindh

1. Darawat Dam (under construction)

2. Karoonjhar Dam

3. Nai Gaj Dam (under construction)

4. Chotiari Dam

Details of WAPDA ongoing and future projects can be obtained from Wapda web sites

http://www.wapda.gov.pk/htmls/ongoing-index.html and

http://www.wapda.gov.pk/htmls/future-index.html respectively. Details of few dams in

included below.

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.24: Layout and cross section of Mangla Dam. (Source: Agha, 1980)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.25: Layout plan and cross section of Tarbela Dam. (Source: Agha, 1980)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.26: Layout plan and cross section of Hub Dam. (Source: Agha, 1980)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.27: Layout plan and cross section of Khanpur Dam. (Source: Agha, 1980)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.28: Layout plan and cross section of Simly Dam. (Source: Agha, 1980)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.29: Layout plan and cross section of Bolan Dam. (Source: Agha, 1980)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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Figure 1.30: Layout of Kalabagh dam (source: Wapda, 1988)

TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION

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1.14.1 Simly Dam data

1. Location : on Soan River 35 km North-east of Islamabad

2. Main purpose: Water supply to Islamabad.

3. Construction: Started 1972, completed 1982

4. Project cost: Rs. 643 million

5. Catchment area = 150 sq.km

6. Gross storage at 2315 elev = 33,115 AF

7. Live storage at 2315 ft elev = 27,708 AF

8. Dead storage : El= 2233 ft and cap = 5,407 AF

9. Reservoir length = 6 km

10. Water supply = 37 MGD

11. Sediment load = 221 AF/year (against est of 331.5AF/y)

12. Dam = zoned earth and rock fill

13. Max Height = 263 ft

14. Crest length = 1010 ft

15. Crest width = 30 ft

16. Crest elevation = 2330 ft SPD

17. Main Spillway: Ogee crest length = 110 ft, Crest elev = 2295 ft

18. Discharge capacity = 45,000 cfs

19. Gates: 3 x 32x25 ft

20. Energy dissipation: chute and two basins in tandem

21. Auxiliary spillway: free overflow weir 459 ft long at crest, crest elev = 2317 ft, Max

Q = 35800 cfs

22. Diversion: Horse shoe tunnel 28 ft dia, 594 ft long and RCC lining

1.14.2 Diamer Basha Dam Project

Location = 40 km d/s of Chilas and 300 km u/s of Tarbela

Dam type: Roller Compacted Concrete gravity (with small curve)

Height = 272 m, crest length = 939 m

Reservoir level = 1160 m

Gross capacity = 8.1 MAF (10 BCM)

Live capacity = 6.4 MAF (7.9 BCM)

Dead storage level = 1060 m

Spillway: Ogee type with flip bucket and plunge pool with 14 Nos. radial gates 11.5 m

x16.24 m

Outlets: low levele – 2, sluicing – 5

Installed capacity = 12 x 375 = 4500 MW (2 underground type powerhouses, one on each left

and right abutment)

Annual generation = 18,000 GWH/yr

Est cost = US$ 8.5 billion

1.14.3 Bunji Dam

Location: on Indus river near Gilgit

Dam height = 180 m

Type: RCC gravity

1.14.4 Mirani Dam Project

Owner: WAPDA

Design consultants: JV of NESPAK-ACE-Binie Black & Montgomery

Contractor: M/s DESCON on EPC/Turnkey basis (fixed price)

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Location: District Kech in Central Makran Range of Balochistan. (30 km west of Turbat) at

longitude 62-41-38.46 E, and latitude 25-56-31.16 N

River system = Dasht River in (Fed by Kech River and the Nihing River)

Hydrology

Catchment area = 7,964 sq. miles,

Average annual rainfall = 4.2 inches

Average annual flow = 223,000 acre feet

Reservoir

Gross storage = 302,000 AF (373 Million m3)

Live storage = 52,000 AF (64 Mm3)

Av annual releases = 114,000 AF

Dam

Type = Earth-Rock fill CFRD

Height = 127 ft (39m)

Length at Crest = 3,350 ft (1020 m)

Crest top width = 35 ft (11 m)

Spillway

Type = overflow

Clear waterway = 344 ft

Design capacity = 205,800 cfs

Max capacity = 384,300 ft

Outlet

Tunnel dia = 8 ft

Capacity = 377 cfs

Others

Access road = 43 km

Irrigation system: gravity lined channels: command area = 33,200 acres

Right bank command area = 20,800 acres [236 cfs]

Left bank command area = 12,400 acres [141 cfs]

Completion = July 2002 to October 2006;

Project cost = 101 Million US $

1.14.5 Jammergal Dam

Owner: Small Dams Organization, Punjab Irrigation and Power Dept.

Location: Jammergal Kas (6 km N of Darapur village from Rasul-Jhelum Road) Distt Jhelum

Catchment area = 5.86 sq. mile (15 sq.km)

Av annual rainfall = 230 mm

Av Ann sediment = 5.47 AF/sq.ml

Max routed inflow = 2145 cfs

Gross storage = 3152 AF

Dead storage = 1502 AF

Live storage = 1650 AF

Normal Res level = 891 ft

Dead storage level = 879 ft

Pond area at NPL = 175 acres

Pond area at dead level = 97 acres

Main dam type = earthfill homogeneous

Max Haight = 62 ft

Length at top = 460 ft

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Top width = 20 ft

HFL = 897 ft

Dam top level = 903 ft

Spillway = chute type ungated

Length spillway crest = 55 ft

Max capacity = 2145 cfs

Outlet: pipe outlet of 2 ft dia at 879 ft level Max Q = 7.25 cfs

Irrigation command area = 925 acres

Crop intensity: Kharif – 53%, Rabi – 67%, annual – 120%

Main irrigation channel length = 15,400 ft (with concrete/brick lining)

1.14.6 GOMAL ZAM DAM (http://www.wapda.gov.pk/htmls/ongoing-index.html )

1. LOCATION OF DAM Khajuri Katch on Gomal River

2.MAIN COMPONENTS

a) DAM

Height 436.4 Ft.

Length 758 Ft.

Type Roller Compacted Concrete Curved

Gravity Dam

b) RESERVOIR

Gross Storage 1.140 MAF

Live Storage 0.892 MAF

C) Irrigation System

Length of Main Canal 60.5 Km

F.S. Discharge 848 Cusecs

Length of Distributaries 204 Km

Culturable Command Area 163,086 Acres

d) Power House

Installed Capacity 17.4 MW

e) BARRAGE

Length of Barrage 620 ft.

3. PROJECT BENEFITS

Irrigated Agriculture Development 163,086 Aces

Power Generation 90.9 GWH.

Flood Control

4. PRESENT STATUS Works in progress

1.14.7 AKHORI DAM LOCATION: Akhori Dam site is loacted near Akhori Village across Nandna Kas, a small

tributary of Haro River in Attock District of Punjab.

OBJECTIVES: (i) Storage of water for: a. Supplementing Indus Basin Irrigation System

and (ii) Power Generation

SALIENT FEATURES

Main Dam

Dam Type Earth & Rock Fill

Height 400 feet = 122 m

Length: 3.23 mile = 5.16 km

Gross Storage 7.6 MAF

Live Storage 6.00 MAF

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Saddle Dam

Height 213 feet

Length 4.78

Conveyance Channel

Conveyance Channel Length 23 Miles (37 Km) (from Tarbela to Akhori dam)

Conveyance Channel Capacity 60,000 Cusecs

Bed Width 249.3ft (76 m)

Depth 32..8ft (10 m)

Installed Capacity

Hydel Power Potential 600 MW (2155 GWh/Annum)

Environmental and Resettlement

No of Affectees 55800

No of Houses 9270

Land 65976 Acres

Roads 102 Kms

Estimated cost US$ 4.40 Billion

Construction period – 5 years

Current Status

- PC-II approved for Rs. 194.804 million by CDWP through circulation in March 19, 2004.

- Final Feasibility Study Report has been received on Jan. 26,2006.

- PC-II for Detailed Engineering Design and Tender Documents of the Project amounting

to Rs. 818.00 Million submitted on June 23, 2006 for approval of ECNEC.