Question

Building a dam is one method of regulating the flow of a river to control flooding. Dams and their reservoirs may also provide recreational oppor- tunities and water for irrigation and hydroelectric power generation. a. When a dam is built, how will the behavior of the stream likely change upstream from the reservoir? b.Given enough time, how might the reservoir change? c. What are some possible environmental impacts of building a dam an a large river?

Answer 1

a) The behavior of the stream towards the upstream of the reservoir is as follows:

• The width of the stream increases due to accumulation on the lower side.
• The depth of the stream level increases (i.e. river bed deepening) due to accumulation on the lower side.
• The speed/flow of the water in the river decreases due to the barrier on the downstream side.
• The erosion and cutting of lands/plants may increase due to expanding and increasing the water level.
• Sediment load increases on the upstream side. etc.

b) After enough time, the characteristics of the reservoir may change such as leakage/cracks/fractures may induce on the porous and permeable soil containing side and on the constructed dam walls. The water holding capacity of the reservoir/dam may reduce over the time being due to the aging of the dam. Or sometimes the permanent natural damming also may create after enough time. The pore-pressure of the reservoir increases due to which the water-bearing strength of the reservoir reduces.

c) It has been observed that after the building of a water dam many of the places are facing reservoir-induced earthquakes. Similarly, the downstream region becomes always in a threat of flash-flood in case the gate of the dam gets opened naturally or accidentally. Similarly, the ecological condition and the microclimate also changes. The production of fishes in the upstream side increases while the downstream side faces low production of fishes. The soil/land erosion on the upstream side increases and the pore-pressure of that particular region increases which may cause instability on the land. The population of aquatic and terrestrial animals in the downstream side decreases due to low water availability. Similarly, the water-table on the downstream side goes deeper.