SOME MINOR DAMS
- Arch dam, and buttress dams come under the category of medium dams, although their use is not very common.
- They have been discussed quite in details.
- Earth dams and gravity dams are the most commonly used dams.
- They will be discussed in their full perspective in subsequent chapters separately.
- Steel dams and timber dams are also sometimes adopted but only as a temporary measure of storing water.
- A brief description of steel and timber dams which are considered as minor dams have been given here.
1. Steel dams.
- These dams are not in common use.
- No dam in Indian has yet been constructed of steel.
- In USA some dams had been constructed in steel in early part of this century.
- These dams consist of a deck slab made of steel plates.
- These plates are supported by inclined struts.
- These dams may also be of cantilever type.
- In this, a frame work of steel sections is installed in the rigid foundation and deck plate is fixed on them.
- In this case tensile forces one induced in deck plate and girders.
- They are cheaper than other rigid dams.
- They can be built in very short time with modern methods of fabrication.
- They are more adaptable in case of unequal settlement of foundation.
- They are more leak proof.
- Frost action does not have any adverse effect on steel.
- They can be repaired easily by welding.
- Life is shorter than concrete or masonry dam.
- They require constant maintenance.
- They are not as adaptable to vibrations due to spilling water.
- This is because they are too light.
- They have to be anchored with foundation.
- Bearing stresses are excessive as bearing are in this case is very small.
- They are also a sort of temporary dams.
- They consist of a frame work of wooden bullies and planks.
- Timber dams are usually of three types.
1. Rock Filled Crib Timber.
- In such dams, crib piers of wooden members are erected at centre to centre distances of 2 to 2.5 m.
- In order to impart stability to the piers, rock boulders are filled in the open spaces left in the wooden members.
- After having erected all the crib piers, along the centre line of the dam, timber planks are fixed to prepare the face for retaining water.
- If rock foundation is available at the site, the bottom of the cribs is anchored with the rock.
- In case of earth foundation, sheet piles are driven both at the U/S as well as D/S side of the cribs.
- System of sheet piles or that of anchoring with rock foundation is essential to maintain the cribs in position.
2. Beaver Type Timber Dam.
- This dam does not involve even driving of sheet piles or anchoring with foundation rocks.
- This dam is suitable for small heights and also where plentry of timber is easily available.
- The stock is finally covered on water face by wooden planks.
- To avoid scouring and also to add to the stability of the dam, the lower U/S end should be covered with boulders and sand.