Types and Choice of Dams

Types and Choice of Dams

A dam is a thick wall made of reinforced concrete (R.C.C), earth and stone masonary to raise the water for storage at high head. It is built across the river.

Dams are classified as :

1. Fill dams :

1. Earth dam
2. Back-fill dam

2. Masonary dams :

1. Gravity dams
2. Buttress dam
3. Arch dams

3. Timber dams

Selection of Site of Dams :

Following points must be considered while selecting the site of dams :

1. It should be located at the neck of river.
2. Soil bearing capacity should be high.
3. Material for construction are available/accessable at site.
4. Site should have transport and communication facilities.
5. Good catchment area should be available on upstream side.
6. It should be away from earthquake zone.
7. Minimum disturbance to people, submergence of area.
8. It should disturb minimum ecological balance.
9. It is economical to construct.

Choice of Dams :

1. Gravity Dams : These are constructed by R.C.C. or stone masonary. The water thrust is resisted by gravity The cross – section of solid gravity dam is shown in Figure A. Because of its weight it needs a solid rocky foundation . The resultant force of weight, W and water thrust, P should intersect the base within middle third of its base line for stability of dam. Advantage of this type of dam is that they can be constructed faster with high quality of construction.

Figure A

2. Buttress Dam : Figure B shows a buttress dam. It has flat deck laid on supporting structure called buttresses. It is also called as hollow gravity type dam. The weight of water P on the deck is transmitted to buttresses as thrust.

Figure B

These dams are cheaper than masonary dams since required much less concrete.

3.  Arch Dam : Arch type masonary dam is shown in Figure C. These are generally not used since construction of such dams require very narrow valley with steep slopes of solid rock so that it can resist the large thrust of water.

Figure C

4. Earth Dam : These dams are constructed for small hydro plants upto 70 m height. These are constructed of earth fill with wide base.

Figure D

Since these type dam require large volume of earth material, such material should be available near the site of dam construction. The side slope of dam are done by stone pitching.

Advantages of earth dam are that these are cheap in construction compared to masonary dam and have long life if protected from corrosion.

Disadvantages are that it has more seepage losses and it may be subjected to serious damage from erosion by water. It is not suitable for spill way structure.

5. Rock – fill Dam : It is constructed from loose rock of all sizes. It has trapezoidal shape with wide base with a water tight section to reduce seepages. It is suitable for mountainous regions where all sizes of rocks are available.