Dam is a solid barrier constructed at a suitable location across a river valley to store flowing water. Storage of water is utilized for following objectives: Hydropower Irrigation Water for domestic consumption Drought and flood control For navigational facilities Other additional utilization is to develop fisheries

1. DAMS

2. Dams and reservoirs - literature
• Bell F.G., Engineering geology and
geotechnics

3. Dams
Dam is a solid barrier constructed at a suitable
location across a river valley to store flowing
water.
• Storage of water is utilized for following objectives:
• Hydropower
• Irrigation
• Water for domestic consumption
• Drought and flood control
• For navigational facilities
• Other additional utilization is to develop fisheries

4. Structure of Dam
Heel
Gallery
Toe
Spillway
(inside dam)
Crest
NWL
Normal
water level
MWL
Max. level
Free board
Sluice way
Upstream Down stream

5. Parts of a dam
• Heel: contact with the ground on the upstream side
• Toe: contact on the downstream side
• Abutment: Sides of the valley on which the structure of the dam rest
• Galleries: small rooms like structure left within the dam for checking
operations.
• Diversion tunnel: Tunnels are constructed for diverting water before the
construction of dam. This helps in keeping the river bed dry.
• Spillways: It is the arrangement near the top to release the excess water
of the reservoir to downstream side
• Sluice way: An opening in the dam near the ground level, which is used to
clear the silt accumulation in the reservoir side.

6. Dams: forces applied
• Vertical static forces
• Lateral force applied by water body
• Dynamic forces
– wave action
– overflow of water (controlled by spillway
channels)
– earthquakes and tremors
– ice/freezing

7. CLASSIFICATION OF DAMS

8. ACCORDING to the SIZE of the DAM
1. Large (Big) dam
2. Small dam
• International Commision on Large Dams, (ICOLD) assumes a dam as big
when its height is bigger than 15m.
• If the height of the dam is between 10m and 15m and matches the
following criteria, then ICOLD accepts the dam as big:
• If the crest length is bigger than 500m
• If the reservoir capacity is larger than 1 million m3
• If the flood discharge is more than 2000 m3/s
• If there are some difficulties in the construction of foundation

9. ACCORDING to the STATICAL DESIGN of DAM
BODY
• Gravity Dams
• Arch Dams
• Butress Dams
• Embankment Dams
• Composite Dams

10. Dams: types
• Gravity dam: rigid monolithic structure
– Trapezoidal cross section
– Minimal differential movement tolerated
– Dispersed moderate stress on valley floor and
walls
• Arch dam: high strength concrete wall
– Convex faces upstream
– Thin walled structure
– Relatively flexible
– Huge stresses imposed on valley walls and floor
• Earth dams: bank or earth or rock with
impermeable core
– Core of clay or concrete, extended below ground
– Sand or gravel drains built to cut fluid pressure
– Low stress applied to valley floor and walls

11. TYPES OF DAMS
• Gravity Dams:
• These dams are heavy
and massive wall-like
structures of concrete
in which the whole
weight acts vertically
downwards
Reservoir
Force
As the entire load is transmitted on the small area of foundation, such dams are
constructed where rocks are competent and stable.

12. • Bhakra Dam is the highest
Concrete Gravity dam in
Asia and Second Highest in
the world.
• Bhakra Dam is across river
Sutlej in Himachal Pradesh
• The construction of this
project was started in the
year 1948 and was
completed in 1963 .
• It is 740 ft. high above the deepest foundation as straight concrete dam being more than three
times the height of Qutab Minar.
• Length at top 518.16 m (1700 feet); Width at base 190.5 m (625 feet), and at the top is 9.14 m (30
feet)
• Bhakra Dam is the highest Concrete Gravity dam in Asia and Second Highest in the world.

13. Buttress Dam:
• Buttress Dam – Is a
gravity dam reinforced by
structural supports
• Buttress - a support that
transmits a force from a
roof or wall to another
supporting structure
This type of structure can be considered even if
the foundation rocks are little weaker
 Buttress Dams use multiple reinforced
columns to support a dam that has a
relatively thin structure. Because of this,
these dams often use half as much
concrete as gravity dams

14. • These type of dams are
concrete or masonry dams
which are curved or convex
upstream in plan
• This shape helps to transmit
the major part of the water
load to the abutments
• Arch dams are built across
narrow, deep river gorges, but
now in recent years they have
been considered even for little
wider valleys.
Arch Dams:
 Arch Dams utilize the strength of an arch to
displace the load of water behind it onto
the rock walls that it is built into.

16. Earth Dams:
• They are trapezoidal in
shape
• Earth dams are
constructed where the
foundation or the
underlying material or
rocks are weak to support
the masonry dam or
where the suitable
competent rocks are at
greater depth.
• Earthen dams are
relatively smaller in height
and broad at the base
• They are mainly built with
clay, sand and gravel,
hence they are also
known as Earth fill dam or
Rock fill dam

17. EMBANKMENT DAMS
(Rock Fill or Earth Fill Dams)
• They are mostly composed of natural materials such as,
clay, sand, gravel etc...
• Impervious core is placed in the middle of the
embankment body
• Generally riprap is used to control erosion

18. COMPOSITE DAMS
• Composite dams are combinations of one or more dam types.
Most often a large section of a dam will be either an
embankment or gravity dam, with the section responsible for
power generation being a buttress or arch.
Gravity & Rock Fill

19. Dams and reservoirs
Reservoirs
• Site selection
• Leakage from
reservoirs
• Sedimentation
• Stability: effect of
raised WT
Dams
• Types
• Forces on a dam
• Geology and dam sites
• Rock types and dams
• Dams on soils
• Ground improvement

20. ENGINEERING GEOLOGICAL STUDIES for DAM
CONSTRUCTION

21. RECONNAISSANCE STUDY
1. Evaluation of the data having at archives
2. Field investigation for limited time (Reconnaissance Study)
3. Some maps in small scale, for example 1/25.000 or
1/50.000
4. Some hydraulic data about
a. Basin
b. Precipitation area
c. Runoff, maximum discharge
5. Some approach to the reservoir area, dam site and type of
dam and height of dam...etc
6. Photogeological studies
7. A preliminary report

22. PRELIMINARY STUDIES at the RESERVOIR AREA
and DAM SITE
1. Dam site investigations
1. Location of dam axis
2. Location of diversion tunnel
3. Location of spillway
4. Location of powerhouse...etc
2. Geological studies
3. Geophysical surveying
4. Underground investigations
1. Boreholes
2. Investigation galleries
3. Pitholes
5. Surveying for materials
1. Field surveying
2. Laboratory tests

23. 6. Slope stability investigations
7. Earthquake hazard & risk analysis
8. Environmental studies
9. Leakage possibilities from reservoir area
10. Leakage possibilities from dam site
11. Erosion, sedimentation & siltation

24. DETAILED INVESTIGATION at DAM SITE
1. Topographic surveyings
2. Geological mappings
3. Underground explorations
Boreholes, adits....etc
4. Hydrogeological studies
5. Slope stability analysis

25. FACTORS AFFECTING to the PLACE of the DAM
AXIS
• Topography
• Geology
• Materials
• Spillway location availability
• Derivation
• Sediments in the flowing water
• Water quality
• Expropriation costs
• Earthquake possibility
• Downstream water rights

26. Site Selection – Geological Consideration
• Narrow valley
• Bed rock at shallow depth
• Competent rock to offer stable foundation
• Proper Geol structure

27. structure
• Horizontal strata -- desirable – load of dam
acts perpen to strata.
• Alternate competent (qtzite) and incomp
(shale) not desirable
• Beds with gentle upstream dip = ideal,
resultant force acts perpen / oblique to
bedding plane, percolation of water directed
upstream towards res

28. structure
• Beds with gentle downstream dip =
undesirable
• WHY?

29. Reservoirs: purpose
• Water storage
• Flood prevention
• Power

30. Reservoirs: site selection
• Hydrological considerations
• Fundamental controls
– topography
– climate
– geology
Water
added
Net amount of water
available for storage
Water
subtracted
Rainfall in river
basin
Infiltration
Evaporation
Transpiration
Runoff

31. Reservoirs: leakage
Water
added
Leakage from
reservoir
Water
subtracted
-
Rainfall in
river basin
Infiltration
Evaporation
Transpiration
Net amount of water
available for storage
Runoff
-
1. Dam bypass
2. Water table effects

32. river
reservoir
before
after
water table divide
Leakage to next valley
Bedrock with a water
table and finite
permeability
new
water
table
Reservoirs: water table leakage-1

33. river
before
Bedrock with low
permeability: aquiclude
High
permeability
layer
Water table in aquifer
reservoir
after
High
permeability
layer
Modified water table in aquifer
Leakage to next valley
Reservoirs: water table leakage-2

34. Most Important
• River is Effluent or Influent
• Influent = river feeds the GW
• Effluent = river is fed by GW
• Influent river = percolation will occur

35. Silting problem
• Measures :
1. Terracing of slope and construction of
retaining wall
2. Check Dam settling basins
3. Diversion of sed-loaded water