Factors influencing flood risk Flashcards
what are the human factors that influence flood risk?
-urbanisation
-deforestation
-agriculture
what are the physical factors that influence flood risk?
-precipitation
-geology
-steep slopes
why does precipitation cause flooding?
torrential rainstorms can lead to sudden flash floods as river channels cannot contain a large volume of water, steady rainfall over several days can also lead to flooding
why does geology cause flooding?
impermeable rocks encourage water to flow overland and into river channels, this speeds up water flow and makes flooding more likely
why does steep slopes cause flooding?
in mountain environments steep slopes encourage a rapid transfer of water toward river channels, this increases the risk of flooding
why does urbanisation cause flooding?
building on a flood plain creates impermeable surfaces such as tarmac roads, water is transferred quickly to drains and then into urban river channels, this rapid movement of water makes flooding more likely
why does deforestation cause flooding?
much of the water that falls on trees is evaporated or stored temporarily on leaves, trees also use water when they grow, when trees are removed much more water becomes available and increases flood risk
why does agriculture cause flooding?
in arable farming, soil is left unused and exposed to the elements, this can lead to more surface runoff, this increased if the land is ploughed up and down steep slopes, as water can flow quickly along furrows
what’s a hydrograph?
it shows how a river’s discharge changes in response to a precipitation event
peak rainfall
highest amount of rainfall per time unit
rising limp
shows how quickly the discharge rises after a rain storm event
lag time
the time difference between the peak rainfall and peek discharge
falling limb
shows the reduced discharge once the main effect of runoff has passed
base flow
the normal flow of a river when its water level is being sustained by a groundwater flow
bankfull discharge
will be drawn as horizontal line marking the level of discharge above which flooding will occur as the river will burst its banks
