Definition |
Storm hydrographs chart the relationship between a rainfall event and its discharge in a river channel. The measurement used is cumecs - cubic metres per second.
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Key Terms
- Baseflow - river flow away from flood periods. Reaches the channel via slow throughflow and from the water table.
- Flood - temporary excess of water that spills over the riverbanks onto land.
- Lag-time - The time interval between the peak of the rainfall event and the maximum discharge. It can be affected by channel shape and drainage basin shape.
- Peak-flow - the peak volume of water flowing through a channel. steep catchments cause the highest peaks on a hydrograph.
- Rising limb - reflects a prolonged increase in discharge in the channel
- Recession - the falling limb, denotes the end of the stormflow and the return to normal discharge through the channel.
Factors affecting the storm hydrograph
- Rainfall - The higher the amount of rainfall, the greater the discharge.
- Drainage basin - big basin = greater discharge, elongated basin = steady discharge, large and symmetrical basin = flashy discharge.
- Human activities - input of water into a channel by land drainage increases discharge. storage of water in reservoirs decreases discharge. Urbanisation and deforestation both increase discahrge. Tarmac increases overland flow because it is an impervious surface, and deforestation decreases interception.