Definitions:
● Precipitation = any form of moisture reaching the ground (eg/ snow, rain, sleet or hail)
● Interception = water being prevented from reaching surface by trees/grass
● Surface storage = water held on ground ( eg/ puddles)
● Infiltration = water sinking into soil /rock from ground surface
● Soil moisture = water held in soil layer
● Percolation = water seeping deeper below surface
● Groundwater = water stored in rock
● Transpiration = water lost through pores in vegetation
● Evaporation = water lost from ground /vegetation surface
● Surface run-off/overland flow = water flowing on top of the ground
● Throughflow = water flowing through the soil layer parallel to surface
● Groundwater = water flowing through rock layer parallel to surface
● Water table = current upper level of saturated rock/soil
Factors increasing flood risk:
● Bands of depressions passing over UK at frequent intervals
○ Result in continuous heavy rain
○ Saturated soil → can no longer store water
○ Increases surface runoff
○ Rainwater enters river quicker → higher discharge and floods
● Sudden bursts of heavy rain
○ Infiltration rate is too slow to cope
○ Occur after a period of drought that bakes soil hard
○ Surface runoff occurs → discharge increases quickly and flash floods occur
● Prolonged light rainfall → may cause floods if there is a lot of previous rainfall
● Sudden snowmelt → release of stored water which increases surface runoff
Geology and relief:
● Geology = rock type
○ Mountains
■ Impermeable rocks (eg/ slate)
■ Thin soils
■ Little vegetation for interception
○ Low lying areas
■ Impermeable clay soil
■ Vegetated
■ Soil compacted → difficult for infiltration
○ Permeable rock areas
■ Less likely to flood
■ Water passes through these rocks
● Relief = height and slope of land
● Steep slopes → surface runoff occurs before rain has time to infiltrate
● Low-lying flood plains → high flood risk as not enough gradient to remove water