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Chapter: Civil - Water Resources and Irrigation Engineering - Diversion and Impounding Structures

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Clasication of Masonry or concrete dams

1. Gravity dams in which the water pressure are resisted by the weight of the dam only. 2. Arched dams, which are built in the form of horizontal arches and in which water pressures are resisted by the reaction of the abutments at each end of the arches.

Dams are broadly classified into three categories

 

1.     Masonry or concrete dams (Straight and Arched)

2.     Rock fill dams

3.     Earth dams

 

The masonry dams are classified again under two categories

 

1.     Gravity dams in which the water pressure are resisted by the weight of the dam only.

 

2.     Arched dams, which are built in the form of horizontal arches and in which water pressures are resisted by the reaction of the abutments at each end of the arches.

 

 

While investigating for the site for locating any dam for an irrigation project, the following favourable conditions should be looked into:

 

 

1.     The flows in the river during the flow season, should be fully adequate to create a reservoir of sufficient capacity the feed the proposed ayacut under the project.

 

2.     The required capacity of the reservoir, can be secured with a dam of reasonable length and height.

 

3.     The nature of foundations for the dam should be suitable with minimum foundation treatment works. Faulty river bed Zones, and Zones of known seismic activity should be avoided.

 

4.     The Materials required for the construction of the dam should be available reasonably near about, to effect economy in the construction.

 

5.     The selection of site should have adequate facilities for the safe disposal of the surplus water of the river during heavy floods.

 

6.     The selected site should have adequate communication facility to convey men, materials and construction equipment.

 

7.     Three should be no gaps in the foreshore of the reservoir, which require additional constructions.

 

8.     The site should give adequate facilities to locate the off takes for the Main canals.

Elementary Profile of a Gravity dam

 

 

As masonry or concrete dams are unsuitable for withstanding any tensional stresses, they should be designed so that no such stresses are developed at the foundations and also in the body of the dam.

 

The correct theoretical, economic profile of such a dam is a right angled triangle, with the

Upstream side  facing   the  water   being  vertical,

 

b=H/SqRt(p)

 

Where b is the base width of the dam.

 

H = Height of the vertical side of the triangle facing water up to Top.




Figure:

 

The specific gravity of the Masonry with which the dam is constructed.

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