Runoff variation and the flood hydrograph
A flood hydrograph is a graph showing how a river's discharge changes after a rainfall event. Different drainage basins produce very different shaped graphs depending on how quickly water reaches the river.
Real World
During Storm Desmond in December 2015, the River Eden at Carlisle recorded a peak discharge exceeding 1,700 cumecs. The catchment's steep slopes, saturated soils, and impermeable rock produced a very short lag time and steep rising limb on the flood hydrograph.
Exam Focus
When describing a hydrograph, always label lag time, peak discharge, rising limb, and falling limb — examiners award marks for precise terminology.
Essay Framework
Use PEEL to structure every paragraph. Tap each step for guidance and an example.
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