Flood Risk Flashcards

All 6 cards in this deck

What effect does impermeable rock or soil (e.g. granite or clay) have on flood risk?

It increases flood risk: water cannot pass through, so surface runoff increases and reaches the river quickly.

What effect does steep relief have on flood risk?

It increases flood risk: steep slopes give greater, faster overland flow and a shorter lag time, with less time for infiltration.

Why does heavy rainfall cause a greater flood risk than slow, light rain?

Heavy rain rapidly saturates the upper soil, so excess water reaches the river quickly as surface runoff (short lag time); light rain can infiltrate.

Why does urban land use increase flood risk?

Concrete and tarmac are impermeable, so surface runoff is high and drains carry water to the river quickly.

True or false? Planting vegetation in a drainage basin increases flood risk.

False. Vegetation intercepts rainfall and encourages infiltration, lengthening lag time and reducing flood risk.

Why can a long period of steady rain cause flooding even if the rain is not heavy?

The rain gradually saturates the ground, so once the soil is full, later rain cannot soak in. It flows over the surface into the river instead, raising discharge.