really need somebodys help?

Question

this lmy last question but i can't seem to answer
when a dam is built across a river, it raises the local base level of the river to the level of the water in the reservois that forms behind the dam how might changing the base level affect the river's ability to transport eroded material?

Answer 1

Well, I am not the expert on dams but I will share what little I know which I read. When dams are built, a factor is applied to take into account the silting that is going to take place and thus reduce the capacity of the dam to store water. So, silting is a reality. I am not sure what you meant by the base level of the river going up. The upstream side of the dam is the reservoir and the downstream of the dam is the river prior to the dam being built. The downstream river is generally with a reduced flow, esp. in lean seasons. Thus the capacity of the river to sustain the fish and other aquatic life, the capacity of the river to carry effluents etc. which may be discharged into it etc. - all these are affected adversely.

As already mentioned, the upstream gets silted up, all of which doesn't get removed in times of overflow or discharge into canals etc. Dredging is a possible solution, but is technically challenging and is expensive.