Dam Engineering.pptx

Department
of
Civil
Engineering
Course
Course Code: CE-6005
Course Name: HYDRAULIC STRUCTURES
Credit Hours: Theory 3(3-0)
Instructor
Name: Dr. Muhammad Zohaib
Designation: Assistant Professor
Department: Civil Engineering
Email: muhammadzohaib@nutech.edu.pk

Introduction
 A hydraulic structure may be defined as any structure
which is designed to handle water in any way
 This includes the retention, conveyance, control,
regulation and dissipation of the energy of water
 Such water handling structures are required in many
fields of civil engineering
 The principal ones being water supply and
conservation, hydroelectric power, irrigation and drainage,
navigation, flood control, fish, wildlife service’s and certain
aspects of highway engineering

Introduction
 Various equations, based on continuity, energy, and
momentum principles, may be used
 To calculate the most suitable length, width, shape,
elevation and orientation of the structure.
 The application of these basic principles to the practical
problem of the design of hydraulic structures is called
hydraulic design
 Designed and constructed for managing and utilizing
water resources to the best advantage of the human
being and environment

Classification of hydraulic structures
The principal hydraulic structures can be grouped
under the following three main categories :
Heading‐up and Control of water
Conveyance and Navigation works
Storage works

Heading‐up and Control of water
 Their main purpose is to raise the upstream
water level to feed the canals/tunnel
 They also serve in controlling and regulating the
rate of flow and measurement of flow in the
stream.
It comprise:
 weirs
 Barrages

Conveyance and Navigation works
 Structures which are used for transportation and to
transport the fluid it self.
Conveyance and Navigation works includes:
 Pipes
 Open Channel
 Pressure conduit
 Canal system
 Tunnels
 Sewer pipes and etc.

Storage Works
 structures which store water for future use.
 The stored water can be used when the natural
flow is less than the required demand. It comprises:
 Large dams and Tanks

Classification of Hydraulic Structures by function

Dam and reservoir structures
 Dam structures
 Dams is a barrier across flowing water that
obstructs, directs or retards the flow, often creating a
Reservoir.
 The blockage or storage formed, can be utilized
for various water resources development purpose
 The primary purpose of a dam is to provide
safe retention and storage of water.

 The specific main functions /advantages of dams and
reservoirs are:
 Water storage for days, weeks, months, years, and over years for power
generation and sediment control.
 Water supply (municipal, industrial or community water supply,
irrigation purposes)
 Flood control
 Regulation/balancing of river flow (such as navigation, low flow
augmentation)
 Recreation
 Multipurpose

 Construction of the dam have also disadvantage
The disadvantages includes
 Distraction of fauna and flora in the dam valley
 Interference in the landscape through dams and reservoirs
 Change of ground water level
 Strong influence on sediment balance
 Change in water temperature and quality
 Influence on fish
 Displacement of people from reservoir site

 Structure related to Dam includes
 Spillway
 Bottom outlet
 Intake
 Gate and valves
 Service road
 Reservoirs
 Bridge
 Energy dissipaters
 Diversion structures

Figure Schematic diagram of the dam components
1. Reservoir
2. Dam
3. Service Intake
4. Bottom outlet
5. Spill structure
6. Diversion structure
7. Service road

Reservoir
 A reservoir is a large, artificial lake
created by constructing a dam across a river
 Broadly speaking, any water pool or a lake may be
termed as a reservoir.
 However, the term reservoir in water resources
engineering is used in a restricted sense for a
comparatively large body of water stored on the
upstream of a dam constructed for this purpose.
 Thus a dam and a reservoir exist together.
 The discharge in a river generally varies
considerably during different periods of a year

Reservoir
 If a reservoir serves only for one purpose, it is called a
single-purpose reservoir.
 On the other hand, if it serves for more than
one
purpose, it is termed a multipurpose reservoir.

Reservoir
Depending upon the purpose served by a given
reservoir, the reservoir may be broadly classified
 Storage or conservation reservoir: Those are
reservoirs which retain excess supplies during
period of peak flow and can release gradually
during low flows or when the need arises.
 Flood control reservoirs:- store a portion of
flood flows in such a way to minimize the flood
peaks at the area to be protected downstream.
 Multipurpose reservoirs:-are those reservoirs
which are planned and constructed to serve not only
one purpose but various purpose together.

Purposes of storage works
1. Irrigation
2. Hydro-electric power generation
3. Control of destructive floods
4. Low water regulation for navigation
5. Domestic and industrial water supply
6. Recreation
7. Preservation and breeding of useful
aquatic life, etc.

Storage Components
 The reservoir volume is subdivided in to the following parts,
when seen in its vertical section

Storage Components
 Dead storage: The portion of the storage capacity from which
water is not normally withdrawn, in accordance with operating
agreements. It is the storage that lies below the invert of the
lowest outlet and thus cannot be evacuated by gravity.
 Live storage: The volume of storage in which water will be
taken for demand, using service outlet. It is the portion of the
storage capacity in which water will normally be stored and
withdrawn for beneficial uses.
 Surcharge storage: This is required as a reserve between full
reservoir Level and the Maximum Water level to contain the peaks
of floods

Storage Components
 Bottom outlet: The outlet which is mainly used to discharge the
water from the reservoir for the environmental flow and for
flushing of sediments. Some times it is also opened to discharge
when there is flooding on the upstream.
 Service outlet: It is used to discharge the required amount of
water for downstream beneficiaries as their need.

Basic terms
 Yield from a reservoir: is the volume of water which can be
withdrawn from a reservoir in a specified period of time.
 Safe yield (Firm yield): is the maximum quantity of water
which can be supplied from a reservoir in a specified period of
time during a critical dry year.
 Secondary yield: is the quantity of water which is available
during the period of high flow in the rivers when the yield is
more than the safe yield.
 Average yield: is the arithmetic average of the firm yield and
the secondary yield over a long period of time.
 Design yield: is the yield adopted in the design of a reservoir.
The design yield is usually fixed after considering the urgency
of the water needs and the amount of risk involved.

 Reservoirs important function is to store water during
floods and to release it later, i.e., storage capacity is its
most important characteristics.
 The available storage capacity of a reservoir depends upon
the topography of the site and the height of dam.
 To determine the available storage capacity of a reservoir
up to a certain level of water, engineering surveys are
usually conducted.
 The storage capacity and the water spread area at different
elevations can be determined from the contour map
 A contour plan of the area is prepared to a scale of 1 cm =
100 m or 150 m with a contour interval of 1 to 3 m,
depending upon the size of the reservoir
Storage Capacity of the dam

 Area-Elevation Curve
 From the contour plan, the water spread area of the
reservoir at any elevation is determined by measuring the
area enclosed by the corresponding contour.
 The storage capacity of the reservoir at any elevation is
determined from the water spread area at various elevations.
 Generally, a planimeter is used for measuring the area.
An elevation-area curve is then drawn between the surface
area as abscissa (x-axis) and the elevation as ordinate (y-
axis).
 Generally, the volume is calculated in Mm3.
Storage Capacity of the dam

Reservoir Storage Capacity
determination
 The following formulae are commonly used to determine the
storage capacity
 Trapezoidal formula: According to the trapezoidal formula,
the storage volume between two successive contours of areas A1
andA2 is given by
where h is the contour interval.
Therefore the total storage
volume V is
where n is the total number of areas.

determination
Cone formula: According to the cone formula, the
storage volume between two successive contours of
areasA1 andA2 is given by

determination
Prismoidal Formula: According to the prismoidal
formula, the storage volume between three successive
contours is given by
The prismoidal formula is applicable only
when there are odd numbers of areas (i.e. n
should be an odd number).
In the case of even number of areas, the volume up to
the second last area is determined by the prismoidal
formula, and that of the last segment is determined by
the trapezoidal formula.

determination
Example: 1)A reservoir has the following areas enclosed by contours
at various elevation
Elevation(m) 200 220 240 260 280 300
Area (km2) 150 175 210 270 320 400
Determine the volume of the reservoir Use
a. Cone method
b. Trapezoidal
c. prismoidal formula

Dam: Is a barrier across flowing water/river that
obstructs, directs or retards the flow of water, often
creating a Reservoir.
There are various ways of classification of dams.
Some of them are :
i. Classification based on function served
ii. Classification based on hydraulic design
iii. Classification based on material used
iv. Classification based on rigidity
Classification of dams

 Storage dam: ‐ It is a common type of dam constructed to impound
surplus flood water for use in dry period. It may be constructed of a
wide variety of materials such as concrete, stone, earth and
rock‐fill.
 Diversion dam: ‐ It is a dam of smaller height constructed to raise
water level of the river and not for storage or equalization of flow.
 Detention dam: ‐ It is constructed to store water during floods and
release it gradually at a safe rate when the flood recedes.
 Debris dams:‐ is constructed to retain debris such as sand, gravel
and floating woods and the water that passes over the dam is
relatively clear.
 Coffer dams: ‐ it is constructed to divert the water during period of
construction. It is temporary dams constructed for facilitating
construction. It is constructed mainly on upstream but also on
downstream depending the slope of the river at the site
Classification according to use

Overflow dam: They are designed to pass the
surplus water over their crest. They must be
made of materials which will not be eroded
by such discharges .E.g. concrete, masonry
etc…
Non‐overflow dam: They are those which are
not designed to be overtopped. This type of
design extends the choice of materials to
include earth fill and rock fill dams.
Classification according to hydraulic
design

1. Masonry dams: ‐ made of masonry
2. Concrete dams:‐ made of concrete
3. Earth dams:‐ made of earthen
materials
4. Rock‐fill dams:‐ made of rock
5. Timber dams: ‐made of timber
6. Steel dams: ‐ made of steel
Classification according to construction
materials used

Characteristics of concrete dams Gravity dam
 It is constructed from concrete materials
 Its stability is based on its own weight
 The gravity dam section profile is essentially triangular to
ensure stability and to avoid over-stressing of the dam or
its foundation.
 Concrete gravity dams could be straight or curved in plan
 It is suited to wider valleys( relative to arch dam),
provided that excavation to rock is less than about 5m
 It needs sound rock foundation
 Requires imported cement
Characteristics of dams

 Good for narrow valleys.
 it also suitable for wide valleys.
 Smaller construction fill volume (compared to
embankments)
 Construction can takes place irrespective of weather
condition
 Smaller free board (1-1.5m)
 Can be constructed as overflow dam, i.e. can
accommodate spillway, hence cost for separate spillway
reduced.
 Outlet pipe work, valves and other ancillary works can be
provided within the body of the dam
Advantageous of Concrete Dams

 Sensitive to settlement, demanding sound rock
foundation
 Sensitive to earth quake
 Depending on the dam type, it’s construction is
demanding (technical personnel, machine
requirement, form work)
 Bad interference in to natural landscape
 Completed unit costs are much higher than
embankment fills, which seldom balanced by the much
lower volumes of concrete required in a dam of certain
height.
Disadvantageous of Concrete Dams

 Arch dam is dam with upstream curvature which
constructed from concrete materials.
 Stability is obtained by a combination of arch and gravity
action.
 Utilizes the strength of an arch to resist loads placed upon it
by 'arch action‘.
 The strength of the rock mass at the abutments and
immediately down valley of the dam must strong enough.
 It is suited to narrow gorges/ V-shape valley.
 High abutment loading.
 50-85% concrete saved relative to gravity dams.
Characteristics of Arch dam

 The foundations and abutments must be competent not
only to support the dead weight of the dam on the
foundation but also the forces that are directed into the
abutments because of arch action in response to the
forces acting on the dam.
 Arch dam can be classified as
 Single‐curvature arch dams
 Double –curvature arch dams
 Arch‐gravity dams
Characteristics of Arch dam

 Buttress dams require between one thirds and half of
the concrete required for a gravity section, hence
making it more economical for dams over 14m.
 Concrete saved 30-60% relative to gravity dams.
 Threat of deterioration of concrete from the
impounded water is more likely than from a thick
gravity section.
 There is also an elimination of a good deal of uplift
pressure.
 create higher contact stress, needs sound rock.
Characteristics of buttress dam

Characteristics of buttress dam

Load Resisting Mechanism of concrete dams
Gravity Dam

LoadResisting Mechanism of Arch dams

Load Resisting Mechanism of buttress dams

 Any dam constructed of naturally excavated materials placed without
addition of binding material other than those inherent in the natural
material.
 It is suited to either rock or compressible soil foundation and wide valley.
 It can accept limited differential settlements.
 Embankment dams are usually referred to be types such as Earth fill,
Rock fill, and Hydraulic fill.
 Earth fill dam: An embankment dam constructed primarily of compacted
earth in either homogeneous or zoned areas containing more than 50% of
earth.
 Rock fill dam : The term rock fill dam usually represents dams that
contain more than 50% compacted or damped pervious rock
 Hydraulic Fill dam: An embankment dam constructed of earth, sand,
gravel or rock generally from dredged material conveyed to the site of
placement by suspension in flowing water.
Characteristics Embankment dams

Characteristics Embankment dams

 Dams must be planned, designed, and constructed to
operate efficiently
 a. Prior (preceding) to construction Reconnaissance
 The main purpose of such investigations is to screen out
the poorer(minor) alternatives.
 To decide thetypes and amounts of more
expensive and time-consuming data (such as stream
flow records, topographic mapping, and so on) which
need to be collected for making feasibility
investigations of the remaining selectable alternatives.
Phases of Engineering activity for site
investigation and construction of dam

Reconnaissance
Field trips and reconnaissance of dam site, reservoir area and
downstream area.
 Collection and evaluation of existing data Like:-
 Socio-economic
 Political
 Environmental and
 Physical data of the catchment

 Hydrologic data
 Collection and analysis of stream flow (mean monthly flow ) and
precipitation record
 Annual sediment load
 Maximum observed flood level in the river
 Report on damage caused by flooding
 approximate maximum and minimum daily water demand
andAssessment of available yield
 A flood occurring once in 100 years or less may cause enormous
damage. Therefore, stream gauging records of 10, 20 or 30 years
required based on size of dam

 Meteorological Data
 Average monthly temperature
 Average monthly rainfall
 Maximum recorded storm intensities
 Annual rate of evaporation
 Data collection like, precipitation, evaporation,
infiltration and percolation condition of the site.
 Geological Data:
 Geologic map of location site
 Nature and type of rock of foundation and
 abutments(support)
 Geologic condition of dam and Spillway site

 Earthquake information
 Historical seismic information
 Construction material type
 Possible quarry sites for construction materials should be
identified with in a reasonable distance from the construction site
 Miscellaneous data
 Erosion condition in the catchment area,
 Transportation
 Existing facilities and rates
 Local labor

 Preliminary and Feasibility studies
 Detailed investigation of site conditions
 The data collected is used for preliminary design and economic
analysis
 Final selection of dam type, main dimensions, dam site and layout, costs
and etc.
 Final investigation and Basic design
 Completion of detailed site investigations
 Detailed design, cost estimates, construction schedules,
 Development of:
 Basic report
 Tender documents for the construction of civil works (drawings,
specifications, general and special contract conditions)

 b. During Construction
 Detailed (design and construction execution)
 Stepwise detail of dam design ahead of construction.
 Site investigations oriented towards construction.
 Construction activities
 Preliminary installation of contractor at site
 Construction of required infrastructure (road, camp, plant, water and energy
supply, etc.)
 River diversion
 Construction of dam and associated structures
 Commissioning and operation manuals
 Preparation of manuals for testing, monitoring and operation of
 equipment.
 Maintenance and service

Factors governing Selection of site for dam
As dams require huge amount of investment cost, care should be
taken while selecting the suitable site.
 The following factors shall be considered when selecting the
site of a dam.
Topography
 As much as possible, the dam should be located where the river
has narrow gorge which opens out upstream to create a
large reservoir .
Suitable foundation:
 Suitable foundation is necessary for dam site
 The existence of joint patterns in an abutment (their orientation,
inclination and infilling) affect the stability of the dam.

 Rock foundation: ‐Any type of dam can be constructed on good
rock foundation.
• Such foundations have high bearing capacity and resistant to
erosion and percolation and are ideal for all types of dams
 Gravel and coarse sand foundation: ‐ such foundations have
low bearing capacity and earth and rock fill dams are suitable
• As there may be high seepage, cut‐off may be provided
 Fine sand and silt foundations: ‐ it is suitable only for earth and
low height concrete dams.
• As there is settlement, piping, seepage erosion at the d/s toe and
liquefaction failure, measures should be done.

 Clay foundation: ‐ it is not suitable for construction of dam.
These foundations have very low bearing capacity. The
settlement is quite large and hence it needs foundation treatment
before dam construction.
Availability of Technical skills
• At many sites neither skilled contractor nor artisans are available.
• This can preclude the adoption of dams that require intricate
framework or very high quality concrete. The embankment type
dams or a masonry gravity dam may then prove most suitable.

Cost effectiveness
• Site conditions naturally influence the cost of various
types of dam.
•Expenditure for operation and maintenance (including
replacement) of the project.
•The capital cost includes the costs of planning, investigations,
designs, and construction besides the cost of acquiring rights to
the use of water, litigations, and rehabilitation of the affected
people.
•The benefits likely to be received from a water resource project
are have to be known.

•For a very high dam, for instance, the cost may be high. For
concrete dams costs for external spillway can be saved in case of
spillway located at the dam crest. However, standard prices of earth
and rock fill materials in the past have not risen as much as those
of mass concrete dams.
Availability of materials
•The cost of transport of material to the site has to be considered,
for different dam options.

Environmental and related issues
• Environment is best defined as all external conditions
which
affect the existence of all living beings.
•Different living beings affect one another, and the environmental
requirements of different living beings are interrelated
•The environmental, economic and other socio-political issues
associated with reservoir development must in all instances be
acknowledged at the outset and fully addressed thereafter.
•This is especially important in the case of the larger high-profile
projects.
• Especially on cross boundary river

Hydrology
• The possibility of inundation by floods during construction
may favor a concrete dam.
• Where high flow occurs, an embankment dam will require
special and detailed protection; whereas concrete dam could be
overtopped with little damage.

Summarizes dam type characteristics in the
context of selection

Dam Site Assessment and Investigation
•Parties directly involved in engineering of dam activities
are:
- Owner - public or private organization
o Provision of financial resources
o Establishment of general objectives
- Consulting Engineer
o Planning and design
o Construction supervision
- Contractor for civil works
o Construction of required infrastructure
o Construction of civil works
• Assembly of equipment

Spillway site selection
 A good site for spillway should exist at or near the dam
site.
 Availability of construction materials: dam requires
large amount of construction materials and hence, there
should be sufficient amount of construction material with
high quality and quantity at nearby to reduce
transportation cost.
 Water tightness of reservoir: the bed and side of the
reservoir should be water tight to reduce seepage loss
 Submergence area: the area submerged on the upstream
of the dam should be small and should not submerge costly
land and property

Spillway site selection
 Accessibility: ‐ the site should be easily accessible for
transportation of construction material. If there was no
road to the site, access roads should be constructed prior
the construction.
 Sediment rate: ‐ the incoming water should be relatively
free from sediment in order to increase the life span of the
reservoir
 Minimum overall cost: ‐ it should be relatively minimum
cost including maintenance and operation

Foundation of dams and their treatment
 Foundation treatment is a technique of improving the
foundation property for the construction of high concrete
structures.
 For convenience, foundation may be classified as rock,
coarse‐grained materials and fine‐grained materials
foundations
 The commonly adopted foundation treatments are:
 Surface preparation and
 Foundation grouting.

 Surface preparation
 Removing the entire loose soil till sound bedrock is
exposed without damaging the underlying rock.
 If faults, seams or shattered rock zones are detected in the
exploratory geological investigations, special steps and
remedies must be taken to ensure their removal.
 Foundation Grouting
 Pressure grouting is the process of injecting suitable
cementations’ slurries or similar materials into
inaccessible places, such as the underlying formation of
foundation of dams for the purpose of sealing seams,
cracks and fissures or filling voids and also used to
improve the strength and elastic properties of the material
into which it is injected

 In general, grouting for foundation treatment may be
classified as
 Consolidation orArea Grouting and Curtain grouting
 a. Consolidation orArea Grouting
 The objectives of consolidation grouting are to strengthen
the rock, to stop water passage through the disintegrated
rock and to increase bearing strength of the strata.
 It is done in an area, usually the entire dam foundation, by
drilling shallow holes (3 to 15 m deep) on a grid pattern at a
spacing of 5 to 30 m.

 This comparatively shallow and low pressure grouting is
done for the general consolidation of the foundation
before concreting of the dam section and is followed by
high pressure grouting after some concreting of the dam has
taken place.
 It also helps in checking the leakage of high‐pressure
grout used later in the curtain grouting

 Curtain grouting
 Curtain grouting (or high pressure grouting) is done to form
a deep curtain wall or an impervious barrier in the
foundation just down‐stream of the heel of the dam.
 It is high pressure grouting is required and relatively
deeper holes are drilled near the heel of the dam.
 It helps in reducing seepage through the foundation
 and reduces the uplift pressure.
 Holes required for curtain grouting are quite deep. The
holes are usually vertical but some times it could be
inclined. Inclined holes are required to intercept the
inclined joints in the rock to develop an effective grout
curtain.

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