River Environments (Q&A)

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What is the difference between throughflow and groundwater flow? (2m)
Ans: Throughflow is water flowing through the soil whilst groundwater flow is water flowing through permeable rocks and reaching the river. Groundwater flow is slower.

Describe the transfer of water through a drainage basin. Start with the input of water as precipitation. (3m)
Ans: Precipitation occurs in the form of rain, snow, sleet or hail. If it is rain, some is intercepted by vegetation. It will fall slowly to the ground as dripflow. Some is surface storage, some reaches the river by surface run-off. Some infiltrates and is held as soil moisture. It may go as throughflow or percolate to the groundwater storage and reach the river as groundwater flow.

Explain the main physical causes of river flooding. (2m)
Ans: The type and amount of precipitation in a drainage basin system is one factor. If it rains heavily for a long period of time, the soil and rock will be saturated-provided it is permeable. Thus surface run-off will increase, increasing flood risk as well. Severe thunderstorms cause rapid surface run-off and flash floods. If the underlying soil and rock is impermeable, infiltration can't occur. Thus increasing flood risk as surface run-off is fast.

Suggest how human activities in a drainage basin can help to cause flooding. (3m)
Ans: If it is an urban area, there will be impermeable surfaces such as tarmac and concrete. This prevents infiltration and increases surface run-off. Storm drains transport water to the river faster than surface run-off, increasing the river's level and flood risk. The land use of the drainage basin system is important. If it is deforested, there will be more surface run-off, and there will be no interception by vegetation. Thus water will reach the river quicker, increasing risk of flooding.

For a named dam or reservoir project, describe how it is a multi-purpose scheme. 
Name of dam or reservoir project: Three Gorges Dam, Yangtze River, China.
Ans: The Three Gorges Dam is a multi-purpose scheme because it has many uses. It firstly prevents flooding downstream, it also generates HEP-Hydro electrical power, about 8% of China's energy. It creates jobs and improves river transport upstream. China can then transport 10,000 ton vessels 2,000km inland to Chongqing. It also provides water supply for surrounding areas. The dam may be a tourist attraction, tourism brings in money and creates jobs.