P108 - 112

Discharge of a river shows a lot of variation during a year and in the short term. It can fluctuate in a matter of hours in response to periods of rain. It is important to understand that drainage basin hydrological cycle to explain how and why the amount of water in a river is variable.

Precipitation input

Interception storage --> evaporation and transpiration output

Surface storage storage --> surface run-off flow transfer --> evaporation output

Infiltration flow transfer

Soil moisture storage --> throughflow flow transfer

Percolation flow transfer

Groundwater storage --> groundwater flow flow transfer

River carrying to lake or sea output

Storm hydrographs shows how a river responds to a period of rainfall. Flashy rivers repspond rapidly to rainfall so they have a high peak and short lag time. A delayed hydrograph will have a low peak and long lag time.

• Run-off is measured in cubic metres per second (cumecs)
• Precipitation is along the y-axis and time along the x-axis
• Rising limb/falling limb
• Peak discharge
• Lag time is time between peak rainfall and peak discharge

River discharge is influenced by weather (rainfall, temperature, previous conditions), other physical conditions (relief, rock type) and human use.

Lots of rainfall causes high river levels. High amounts of rain saturate soil and underlying rock, but a drizzle will give…