Throughflow
Throughflow (also called interflow) is the lateral movement of water through soil layers and the upper soil profile, moving downslope toward river channels. It occurs when soil is saturated or nearly saturated and water moves sideways along soil horizons rather than percolating vertically downward.
Real World
During the 2015 Cumbrian floods, saturated hillside soils in the Lake District redirected water laterally as throughflow, delivering it rapidly to already swollen rivers like the Eden.
Exam Focus
When explaining flood risk, state that throughflow is faster than percolation but slower than surface runoff to show process understanding.
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