Rivers, Floods and Management:
River Drainage and Storm
1 What is River Discharge?
1.1 The volume of water in a
channel passing a particular
point in a given period of
1.2 Values are expressed in cumecs (cubic
metres per second)
1.3 The calculation is: discharge (m3 per second)
= cross-sectional area (m2) x velocity (metres
2 What Factors Affect River Discharge?
2.1 Distance Downstream: In humid environments, river
discharge increases downstream. Main reason for
increase in water are caused by tributaries joining the
2.2 Climatic Characteristics: Snowfall results in time delay as it is being
stored for a long time until snowmelt happens and there is a sudden
surge in discharge. Temperature affects evaporation rates and
2.3 Land Use: Afforestation reduces discharge and make it more constant. Urbanisation increases
discharge because water is transferred rapidly over impermeable surfaces such as tarmac-and
through pipes and sewers.
2.4 Water Abstraction (Removal): This is for domestic use and
the irrigation of crops, this reduces discharge. This can be
seasonal, with greater demand for water in summer months.
2.5 Channel Modification: Constructing a reservoir regulates the discharge and makes it
more constant. The channel itself might also be modified to reduce flood risk e.g. channel
straightening and enlargement tend to increase discharge.
3 The Storm Hydrograph
3.2 This is a graph that shows the
discharge of a river following a