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Physical csuses

a steep-sided channel- a river channel surrounded by steep slopes causes fast surface run-off

a lack of vegetation or woodland- trees and plants take in (drink) water. if there is little vegetation in a drainage basin then the surface run-off will be high

a drainage basic with impermably rock- this means the water cannot pass through the rock , so it will run faster over the surface

a drainages basin in an urban area- these consist largely of concrete which is impermeable and encourages overland flow. drains and sewers take water quickly and directly to the river channel. houses with sloping roofs further increase the amount of run-off