Water (Hydrological) Cycle
The continuous cycle of water between the sea, land and atmosphere.
There are five main processes in the hydrological cycle, these are:
Condensation - Water vapour changes back into water (cloud formation)
Evaporation - The transfer of water from the sea and the land to the air as water vapour
Precipitation - Any form of moisture falling from the atmosphere e.g. sleet, hail, snow, rain
Transpiration - Transfer of water from vegetation to the air as water vapour
Surface run-off - Water flowing over the surface of the earth, e.g. river
In the hydrological cycle water can be stored as snow and ice, in lakes, as ground water and in oceans and seas.
A drainage basin is an area of land drained by a river and its tributaries.
Features of a drainage basin:
Water shed - An area of high land which forms the edge of a river basin
Tributary - A small river flowing into a large river
Confluence - The point where two rivers meet
The source - Where a river starts
Mouth - Where a river flows into (lake or sea)
Ganges/Brahmaputra river basin
[TOP TIP - Make sure you can produce a sketch map of the main features of this river basin!]
Flooding in the Ganges basin - physical factors
- Heavy monsoon rain between April and September
- Tropical cyclones over the bay of Bengal in summer and autumn
- Melting snow in the Himalayas during summer months
Flooding in the Ganges basin - human factors
Deforestation in many parts of the river basin, e.g. Nepal, Bhutan and Northern India. This is a result of population growth (more wood is needed for cooking and heating. Also more forests are cleared for farm land). This has led to increased flooding. This is a result of:
- More erosion of soil as roots no longer hold soil together
- Less take-up of water by plant roots
- Less interception of rain fall by vegetation cover
Positive impact of flooding in Ganges/Brahmaputra river basin
Regular annual flooding is essential to people who live on the flood plain of these rivers, the farming season is planned around the floods, rice is a main crop and requires large quantities of water. Also, when the river floods it leaves behind fertile silt.
Negative impact of flooding in Ganges/Brahmaputra river basin
Case Study - Flooding in Bangladesh - August and September 1988
- Floods covered 80% of the land
- 7 million homes destroyed
- 25 million people made homeless
- 2379 people died
- A quarter of the rice crop was destroyed
- Thousands of kilometres of road were flooded
- Destruction of communications network meant it was impossible to deliver food and medical supplies
Solutions to flooding problem in Ganges/Brahmaputra river basin
Bangladesh Flood Action Plan (FAP) - a plan to try to control the impact of the river flooding Main features of plan:
- 5000 flood shelters built on stilts in areas most at risk
- Improved flood forecasting system using satellite and computers
- Build dams to control river flow and hold back monsoon rain water in reservoirs
- Complete and strengthen embankments along the main river channels to a height of up to seven metres
What might the examiner ask?
- Give a definition of a keyword e.g. confluence
- Explain 3 causes of flooding?
- For an area you have studied describe the impact of flooding.
- For an area you have studied, what was the cause of flooding?