2. DAM
DAMS is an hydraulic structure build up of impervious material to create a reservoir to upstream across
the river to impound water
Dams and Reservoir are complements of each other
Dam are constructed in the mountainous to reach the river where the valley is narrow and foundation is
good
Generally, A hydropower structure constructed at or near the dam site to develop hydropower
Dams are most important hydraulics structure
3. CLASSIFICATION OF DAM
• DAMS are classified based on function being served
• Storage dams
• Detention dams
• Diversion dams
• Debris dams
• Coffer dams
4. STORAGE DAMS
• Storage or conservation dams are constructed to store water during the rainy season. When there is
large flow in the river.
• Storage water is utilized during the period when river water is reduced and less than the demand.
• Water stored in the reservoir is used for various purposes such as irrigation, water supply and
hydropower.
• Storage dams are most common type of dams and in general dams means a storage dam unless
qualified otherwise.
5. DETENTION DAM
• Detention dam are constructed to control flood
it retards the flow in the river on its downstream during flood by storing some flood water
• Thus the effect of sudden flood is reduced to some extent
6. DIVERSION DAM
• Diversion dam are constructed for diverting water of the river to off-taking canal or conduit.
• Diversion dams are usually of low height and has small storage reservoir on its upstream.
• Diversion dam is sort of storage weir which also diverts water and has small storage.
• Sometimes, the weir and diversion dam are same.
7. DEBRIS DAM
• Debris dam is constructed to retain debris material such as sand, gravel and drift wood flowing over the
river.
• Water passing over the debris dam is relatively clear.
8. COFFER DAM
• Coffer dams is not actually a dam. it is rather enclosure constructed around the constructed site to
water so that the construction can be done on dry.
• Coffer dam is thus a temporary dam constructed for facilitating construction.
• Coffer is constructed on upstream of main dam to divert water into a diversion tunnel during the
construction of the dam.
• When the flow during construction of the dam is not much, the site is usually enclosed by coffer dam
and pumped dry.
• Sometimes, coffer dam on the downstream of dam also required.
10. OVER FLOW DAM
• Overflow dam is designed to act as overflow structure
• Surplus water which can not retained in the reservoir is permitted to pass over the crest of the over
flow dam which acts as spillway.
• Over flow dam is made of material which does erode by the action of over flow water
• Cement concrete is generally used in overflow dam and spillway.
• Most of the gravity has over flow section of some length and rest of the length is non overflow dam
• Sometimes, the entire length of the dam of low height is designed as an overflow dam.
• Overflow dam is also called the spillway section.
11. NON –OVER FLOW DAM
• Over flow dam is designed as such that there is no over flow through it.
• Non over flow dam can be built of any material such as concrete, masonry, earth, rock fill, timber.
• Non over flow dam is usually provided in a part of total length of the dam
• Sometimes, non over flow dam is provided for the entire length and a separate spillway is provided in
the flanks or in a saddle away from the dam.
12. CLASSIFICATION BASED ON CONSTRUCTION
MATERIAL
• Masonry dam
• Concrete dam
• Earth dam
• Rock fill dam
• Timber dam
• Steel dam
• Combined concrete cum earth dam
• Composite dam
14. RIGID DAM
• A rigid dam is quite stiff
• It is made up of stiff material such as concrete, masonry, steel and timber
• These dam deflected and deform very little when subjected to water pressure and other forces
15. NON – RIGID DAM
• Non rigid dam is relatively less stiffed as compared to rigid dam
• It is made up of earth and rock fill material
• There are large settlements and deformation in these dam
• Rock fill dam are neither full rigid dam nor fully non rigid
• Sometimes, classified as semi rigid dams.
16. CLASSIFICATION BASED ON STRUCTURE
• Gravity dam
• Earth dam
• Rock fill dam
• Arch dams
• Buttress dam
• Steel dam
• Timber dam
17. GRAVITY DAMS
• Gravity dam resists the water pressure and other forces due to its weight(or gravitational forces).
• Stability of gravity dam depends upon its weight.
• Gravity dam are usually made up of cement concrete.
• In the past, gravity dam are constructed of stone masonry but now it is rarely constructed, except for
very small heights
• Sometimes, gravity dams are generally straight in plane( axis is straight from one abundant to the other)
and the called straight gravity dams
• Sometimes, they are slightly curved in plane with convexity towards the upstream and are called curved
gravity
• Gravity dams are approximately triangular in cross-section, with apex at the top
18. CONTINUE…
• Gravity dam are more expensive than earth dams but are durable
• They are quite suitable for the gorges with steep slopes, they require strong rock foundation.
• If the foundation consist of soil the height of the dam is limited to 20m or so.
• Gravity dam is solid gravity dam when there is no hollow space except for small galleries or shaft
• On the other hand, hollow gravity dam has large hollow spaces left within the body of the dam for the
purpose of reducing the weight and for more effective use of concrete for resisting the stresses
• Hollow gravity dam are similar to buttress dam
19. EARTH DAMS
• Earth dam is made up of earth(soil).
• It resists the forces normally due to shear strength of soil.
• The weight of earth dam also helps to resist the forces , the structural behavior of earth dam is entirely different
• The earth dams are usually built in wide valleys having flat slopes at flanks(abutments).
• Foundation requires less strengthen than gravity dams hence they can be built on the sites where foundation is less strong
• Height of the dam is normally depends upon the foundation material too.
• Normally, have zoned section with an impervious zone called core in the middle and relatively pervious zone enclosing the
impervious zone on both sides.
• Earth dam is built on pervious foundation a concrete wall or steel sheet pile is also provided in continuation of the core
section.
• Drainage filter or rock toe is provided on the downstream to carry away the water that seeps through the dam and its
foundation.
20. ROCK FILL DAMS
• Rock fill dam is made up of rock fragments and boulders of large size
• An impervious membrane is placed on the rock fill on the upstream side to reduce the seepage through the dam
• The membrane is usually made of cement concrete nor of asphaltic concrete.
• Steel and timber membrane were also used but now they are obsolete.
• Dry rubble cushion is placed between the rock fill and membrane for the distribution of water load and support to the
membrane.
• Sometimes rock fill dam has an impervious earth core in the middle to check the seepage instead of Impervious upstream
• Earth core is placed against a dump rock fill.
• It is necessary to provide adequate filters b/w the earth core and rock fill on the upstream and downstream sides so that
the soil particles are not carried out by the water and piping does not occur.
• The side slopes of rock fill dam are equal to the angle of repose of rock it usually taken as 1.4:1 or 1.3:1.
21. ARCH DAMS
• An arch dam is curved in plan , with its convexity towards the upstream
• An arch dam transfers the water pressure and other forces mainly to the abutments by arch action.
• Arch dam is quite suitable for narrow canyons with strong flanks which are capable of resisting the
thrust by arch action
• The arch dam may have a single curvature or double curvature in the vertical plane
• The arch dam of double curvature are more economical and are used in practice
• Uplift pressure is not important factor in the design of arch dam because the arch dam has less width
and reduction in weight due to uplift does not effect the stabilility.
22. BUTTRESS DAM
• Buttress dam are of three types
• Deck type
• Multiple arch type
• Massive head type
23. DECK TYPE BUTTRESS DAM
• It consist of sloping deck supported by buttresses
• Buttresses are triangular concrete walls which transmit the water pressure from deck slab to the
foundation
• Buttresses are compression members
• Deck is usually a reinforced concrete slab supported by the buttresses which are equally spaced
24. MULTIPLE ARCH BUTTRESSES
• In a multiple arch type buttresses dam the deck slab is replaced by horizontal arches supported by the
buttresses
• The arches are of small span and made of concrete
25. MASSIVE HEAD BUTTRESSES
• In a massive head buttresses dam there is no deck. Instead of deck slab upstream edges are flared to
form massive heads which span the distance between the buttresses.
