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River Landscapes in the UK 2 (River discharge and hydrographs (river…
River Landscapes in the UK 2
Floodplains
=areas around the river caused by frequent flooding
levee = when a river floods material is deposited on the banks of the river
estuaries
When there is less water, the river deposits silt to form mudflats which are an important habitat for wildlife.
partially enclosed coastal body of water with other rivers and streams flowing into it
River discharge and hydrographs
river discharge = the volume of water that flows through a river every second
how to decrease river discharge
afforestation so more interception
permeable surfaces so water infiltrates
gentle slopes for more infilitration
high temperatures increase evaporation rate
peak discharge =the time when the river reaches its highest flow
lag time = the delay when the water finds its way to the river
rising limb = discharge is increasing
falling limb = discharge is decreasing
storm hydrograph = a graph that shows how a drainage basin responds to a period of rainfall
peak rainfall = the time of highest rainfall
Causes of flooding
impermeable rock = water can't infiltrate = increased surface runoff = higher discharge
hot, dry conditions and freezing conditions cause hard ground so surface run off increases
urban areas have impermeable surface
lots of surface runoff happens on steep slopes = lag time decrease = discharge increases
previous weather conditions -> lots of precipitation = saturated soil = less water infiltrates the soil = discharge increases
heavy rainfall = lag time decreases = discharge increases
less vegetation = less interception by plants = lag time decrease = discharge increases
Flood management
hard engineering
dams and reservoirs - expensive but controls river discharge
straightening channels - less buildup of water but flooding downstream
embankments - river can hold more water but not completely protective
flood relief channels - reduces flooding in main channel but flooding where they join onto main river
soft engineering
flood warnings and preparation - people can prepare but doesn't stop flooding
flood plain zoning - less buildings close to the river so reduces damage caused but but doesn't stop flooding
afforestation - more interception but expensive
river restoration - less flooding downstream and good for wildlife but floods increase locally
An example of a river valley: River Clyde
source = south uplands
34km from Glasgow
length = 160km
meander = motherwell
oxbow lake = new lanark
waterfall = falls of clyde
floodplain = Glasgow floodplain
An example of a flood management scheme in the UK: Boscastle
why it flooded
there was 200mm if rainfall in one afternoon
car park and deforestation on slopes leading into Boscastle meant that the surface runoff increased and interception and infiltration decreased
management
widened and deepened the bridge
widened and deepened the river
removed debris and dead vegetation
issues with the management
cost £4 million
people were unhappy as new bridge doesn't fit with the historical design
increased biodiversity
