river flooding pg Flashcards
what is river flooding
when the volume of water exceeds the capacity of the river channel and therefore overflows the river banks
what causes river to flood h and p
human
as a result of us altering the db of a river itself
physical
result of natural enviroment
name physical and human causes of flooding
physical
relief, rainfall, rock type, basin size, soil saturation, vegetation
human
deforestation, basin size, urbanisation
urbanisation description
building in areas at risk of flooding - tarmac areas made so water cannot drain and flows into river
agriculture des
arable farming - soil left unused and exposed for periods of time leads to more surface runoff
deforestation des
trees absorb water so if cut down less water is absorbed and will end up in river
rock type des
impermeable rocks don’t allow water to pass through so river more likely to flood because water doesn’t rain but held in river
basin size des
when large able to store more water. if small increased risk of flooding as water capacity is lower
soil saturation des
when soil no longer absorb any more water it becomes saturated and causes flow of water over land into river
relief des
steep slopes allow water run over land quickly leaving little time for water to seep into soil so water enters nearby river
precipitation des
rainstorms can lead to flash floods as river cannot contain increased volume of water
what is discharge measured in?
cumecs meters per sec
what is a flood hydrograph
graph that plots river discharge after storm.
peak discharge def
highest discharge recorded
lag time def
difference between peak discharge and peak rainfall
hard engineering def
strong construction methods to hold back floodwater usually expensive needs maintaining
examples of hard engineering (6)
channel enlargement by dredging embankment concrete lined channel reservoir (caused by dam) afforestation land use zoning
what is soft engineering
more natural ways to reduce impact of flooding on humans with less intervention and more preparation usually sustainable
methods of soft engineering
afforestation (planting trees)
floodplain zoning
what are names of warning levels for flooding and defs
severe flood warning
extreme danger to life and property. stay in upper floors and turn off electricity and leave when possible
flood watch
flooding on low lying land and roads.
flood warning
threat to homes and businesses should move items to upper floors turn off electricity
