Human Interaction with Rivers

An example of human interaction with rivers

Dam building and the development of reservoirs, e.g. The Three Gorges Dam along the Yangtze River in China.

The Three Gorges Dam

Biggest and most powerful dam ever built. Built to control the intense flooding in the region. E.g. 1931, devastating floods killed 250,000.

Impacts of a dam

Impacts the rivers erosion, transportation, and deposition.

River erosion definition

How a river removes material along the bed and banks of the river.

River transportation definition

How the river transports the eroded material.

River deposition definition

How the river leaves behind, or deposits, the eroded material.

How the dam works

The dam works by trapping water, and releasing a small amount, at high speeds.

Result of water being trapped

Flow of water downstream is interrupted and the water now travels through a narrow space creating surges of velocity. This increased hydraulic action, vertical and horizontal, which should not be active at this stage of the river.

Rivers vertically eroding

This causes the river to start eroding into the riverbed again through vertical erosion. This deepens the river channel resulting in entrenched channels that are much lower than the flood plain.

Natural flow

The dam interrupts the natural flow of the river as there is a wall built across the river channel, blocking the river flow.

Accumulation of sediment in reservoir

This reduces river’s ability to carry sediment to the sea and leads to a build-up of sediment behind the dam. This leads to an accumulation of silt in the reservoir behind the dam.

Filtered water

This causes the water there become muddy. As a result, the water here must be filtered and treated if used by humans.

Interruption of deposition

Because sediment is trapped behind the dam walls it cannot be deposited further upstream where this typically occurs. Dam walls cause the deposition to build up behind them instead.

Alluvium in dams

Because alluvium is blocked behind the dam wall, the nutrient-rich alluvium is not reaching the middle and lower stages, meaning the dam is depriving the soil of fertile alluvium.

Soil fertility

Soil fertility is lost as flood plain sediments are not replaced. This directly affects agricultural lands in the region. Farmers must use expensive fertilisers to keep their lands usable.

Deltas

Landforms like deltas are affected because not enough water is reaching them. Therefore, sea water seeps back up the delta and poisons the land with excess salt. This can kill/displace much wildlife that inhabit this area.

Impact of reservoirs

To create a reservoir, a large area of land must be flooded. During the construction of the Three Gorges Dam, over 2 million people were displaced as the locality was flooded.