Rivers, Floods and Management: River Drainage and Storm Hydrograph

Rivers, Floods and Management: River Drainage and Storm Hydrograph

1. What is River Discharge?

   • The volume of water in a channel passing a particular point in a given period of time.
   • Values are expressed in cumecs (cubic metres per second)
   • The calculation is: discharge (m3 per second) = cross-sectional area (m2) x velocity (metres per second)

2. What Factors Affect River Discharge?

   • Distance Downstream: In humid environments, river discharge increases downstream. Main reason for increase in water are caused by tributaries joining the main river.
   • 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 vegetation growth
   • 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.
   • 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.
   • 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

   • This is a graph that shows the discharge of a river following a storm event
   • Characteristics that affect hydrographs:

Images and files in the map