Flooding and flood mitigation

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When **discharge rises above bankfull** so the channel overflows onto the floodplain.

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The **probability** of a damaging flood multiplied by the **harm** (damage, lives) it would cause.

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**Built structures** that control the river — dams, levees, flood walls, channel straightening.

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**Natural and planning** approaches — afforestation, floodplain zoning, river restoration, warning systems.

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A raised embankment that **increases channel capacity**, so more discharge is carried before the river overtops.

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Land-use planning that **keeps housing off the most flood-prone land**, removing risk at source.

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It speeds the flow, so water reaches **downstream** settlements faster — raising the flood peak there.

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Trees intercept rain and aid infiltration, slowing run-off so the **flood peak is lower and delayed**.

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It stops the river spreading locally, so more water is carried faster **downstream**, raising the peak there — risk is transferred.

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Hard = powerful but costly and shifts risk; soft = cheaper and sustainable but slower and less certain against extreme floods.

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Intense rainfall and steep relief (also impermeable geology, a round/compact basin, sparse vegetation).

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Two+ contrasting measures linked to the flood peak, a named scheme, a weighing of effectiveness vs cost/side-effects, and a clear judgement.