Urban water cycle: water movement through urban catchments as measured by hydrographs
Cities change how rainwater moves across the land. A hydrograph is a graph that shows how quickly and how much water flows into a river after rainfall — and urban areas produce a very distinctive, dangerous pattern.
Real World
During the 2007 Sheffield floods, river gauges on the River Don showed lag times as short as 30 minutes after peak rainfall in heavily urbanised upstream areas, compared with several hours in rural tributaries — illustrating the urban hydrograph effect in real time.
Exam Focus
When sketching or annotating a hydrograph, explicitly label lag time and peak discharge and state how urbanisation changes each value.
Essay Framework
Use PEEL to structure every paragraph. Tap each step for guidance and an example.
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