humans and dams

i will discuss how human activities impact river processes

Humans interfere with river processes to control flooding

this can be done by cutting off meanders or building dams

the Mississippi river was very hard to navigate

by cutting off large meanders it shortened the course

since the river’s journey is now shorter, it steepend the slope which meant that the river flowed faster downstream

this lowered flood levels as the water was drained away quicker

despite efforts by the Corp of engineers the river regained 50 miles of its original meanders

the interaction of humans still cuts off 100 miles off the journey of the Mississippi river

humans have also constructed dams to prevent flooding e.g the Poulaphuca dam

a dam is a barrier built across the river

it is used to hold back the flow of the river

water builds up behind the dam to form new artificial reservoirs or lakes

the flow of water through the damn and the river is regulated and controlled via penstocks or gates

the water level in the reservoir behind and in front of the dam can be controlled

they are usually made of concrete

damns can be used to harness hydro-power electricity, a cheap renewable energy

they help reduce the risk of flooding as the water level in the river down stream can be controlled

they also provide a water supply for industrial and domestic use

dam construction can affect the rivers processes both upstream and downstream

dams block the transportation of the rivers load

larger bedload is affected and are first dropped when the river enters the reservoir

suspended load settles on the lake bed

the river has a reduced load downstream after the dam

deposition

the river slows down as it enters the reservoir

this leads to a reduction of needed to transport its load

sediments build up on the lake floor

these fine grained deposits are called alluvium

the reservoir needs to be dredged to remove the sediments

erosion

water flow through the dam means the river has more energy

this leads to erosion downstream

usually a plunge pool may form infront of a dam

flooding has been controlled as a result of dams

when the rainfall is high some of the gates can be closed to reduce the river volume downstream so flooding is less common