Download - DRE-12 Ch-1 Dam Introduction 28-8-2012
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
1
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
2
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
3
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
4
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].
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
5
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
6
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
7
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.
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
8
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
9
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
10
Figure 1.6a: Earthfill embankment dams.
Figure 1.6b: Rockfill embankment dams.
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
11
Figure 1.7a: Concrete dams.
Figure 1.7b: Future Concrete dams.
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
12
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
13
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
14
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
15
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
16
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
29
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
36
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
37
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
38
Figure 1.24: Layout and cross section of Mangla Dam. (Source: Agha, 1980)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
39
Figure 1.25: Layout plan and cross section of Tarbela Dam. (Source: Agha, 1980)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
40
Figure 1.26: Layout plan and cross section of Hub Dam. (Source: Agha, 1980)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
41
Figure 1.27: Layout plan and cross section of Khanpur Dam. (Source: Agha, 1980)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
42
Figure 1.28: Layout plan and cross section of Simly Dam. (Source: Agha, 1980)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
43
Figure 1.29: Layout plan and cross section of Bolan Dam. (Source: Agha, 1980)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
44
Figure 1.30: Layout of Kalabagh dam (source: Wapda, 1988)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
45
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)
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
46
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
47
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
TARIQ. 2012. DAM AND RESERVOIR ENGINEERING Ch-1: INTRODUCTION
48
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.