Fluvial Processes - Leaving Cert Geography

With reference to an example you have studied, describe and account for one way in which humans attempt to influence or control natural processes.

Refer to Fluvial Processes.

Human impact on river processes. People build dams and levees to control river flooding, this has several effects on the operation of natural river processes,

Eg. The Three Gorges Dam in China.

The Three Gorges Dam was completed in 2006, it has affected the natural processes on the Yangtze river.

The dam was built to manage flooding along the river channel and also to generate electricity.

While the dam has prevented the river from flooding by reducing the flow of water, it has interfered with the process of deposition as alluvium that should have been deposited further downstream is now being deposited in the 600km long artificial reservoir that was built behind the dam.

As the fertile alluvium is trapped behind the dam and deposited in the reservoir it also interferes with the natural process of transportation.

Flooding of farmland has been prevented, however, farmland is now deprived of fertile alluvium that would have been transported by the river and deposited during times of flooding.

Farmers now have to use expensive artificial fertilisers to fertilise farmland that used to have a rich supply of fertile alluvium.

The natural habitat of the river Yangtze has also been affected, in 2007 the dolphin has been declared extinct in the river.

Building levees prevents natural flood processes from occouring.                          Eg. The river Rhine in Germany.

Levees are raised river banks that are deposited in the lower stage of a river’s course.

These are natural river landforms, but humans also build levees and raise existing levees to stop a river flooding onto its natural flood plain.

Flood plains are flat, fertile areas. Over time these areas have become densely populated areas and large cities have been built on flood plains eg. Duisburg.

Preventing rivers from over flowing onto their floodplains by interfering with the natural process of flooding has stopped damage to important infrastructure.

But because the levees are so high, the river cannot flood naturally, so it deposits its load on the riverbed. Eventually the bed raises so that the man-made levees are the only thing containing the river and have to be constantly maintained which costs a lot to do.

Floodwater which would normally escape onto the flood plain is now trapped in the river and is funneled downstream where it can easily overflow causing extreme damage.

Levees also cause the river to flow faster as it is constrained by narrower channels. The river Rhine now flows 30% faster.