Rivers and coasts

Hydrological cycle:

It describes the continuous transfer of water vapour from stores such as oceans or lakes into the atmosphere, then back to land as precipitation, finally returning to the original stores.

The hydrological cycle can be seen as a natural system that recycles water and is therefore globally sustainable. However at a smaller scale the smooth flow of the system can be interrupted by short-term extreme climatic events such as:

• Periods of prolonged rainfall can create a surplus of water on the land that may lead to flooding. 
• Periods of drought can cause water shortages that may in turn lead to food shortages in some parts of the world.

The river system:

The river system is the part of the hydrological cycle operating on land. It is made of 4 key parts:

• Inputs: water entering the system through precipitation.

• Stores: water stored in lakes, rocks, soil or vegetation. Storage can be temporary and is linked to the amount of runoff.

• Transfers: Processes that move water through the system,  such as surface run off, infiltration and underground flow

• Outputs: Where water is lost to the system as rivers reach the sea or through evapotranspiration 

KEY TERMS:

• Evaporation - water turning into water vapour
• Evapotranspiration -  the sum of evaporation from the earths surface together with the transpiration of plants
• Groundwater flow - movement of water underground through the rocks
• Infiltration - seeping of water into soil
• Interception - collection of water by vegetation
• Precipitation - moisture that falls from the atmosphere in any form
• Surface runoff - all water flowing on the earths surface
• Sustainable - capable of existing in the long term
• Through-flow - movement of water through the soil
• Transpiration - loss of moisture from plants
• Water table - the upper level of underground water

What is a drainage basin?

An area of land that is drained by a river and its tributaries. Precipitation falling within the catchment area finds its way into streams and rivers that flow towards the sea. 

The edge of a drainage basin is called a watershed and is often a ridge of higer land. Precipiation falling on the other side of the high land flows into a neighbouring drainage basin. 

Main features of a drainage basin are:

• Watershed -The boundary between two drainage basins.
• Estuary - Part of a river that is tidal
• Mouth - Where a river enters the sea
• Tributary - A stream or river that flows into a larger stream or river
• Source - Where a river begins
• Confluence - where two or more streams or river channels meet.

How are drainage basins adapted for human use?

Water is one of the worlds most important natural resources for human survival and economic development. Consequently many drainage basins are used as a source of water and a means of dealing with waste water, especially in towns and cities. Drainage basins are adapted in many ways, including:

• bulding dams and reservoirs
• irrigation schemes and agriculture
• widening abstraction for industry and power…