✅rivers Flashcards
what physical factors affect flood
heavy rainfall —> water arrives too quickly for it to infiltrate so there’s a lot of surface run off which increases discharge
geology (rock type) —> some are impermeable e.g. granite so run off is increased
prolonged rainfall —> saturate soil so rain can’t infiltrate —> runoff into river channels
relief —> water will reach river channel quicker because it can flow down faster —> increases discharge
what are the human factors of flooding
land use e.g. agriculture, deforestation and urbanisation
buildings made from impermeable materials —> increasing surface run off —> increasing discharge
trees intercept rain and take it in to store water —> cutting it down increases water that enters the river channel
hard engineering
man made structures built to control flow of rivers and reduce flooding
how to reduce flooding using hard engineering
dams and reservoirs
channel straightening
embankments
flood relief channels
what are dams and reservoirs
dams- barriers built across rivers
reservoir- artificial lake formed behind dam
benefits of dams and reservoirs
store water and prevent floods downstream
used to generate hydroelectric power (HEP)
disadvantages of dams and reservoirs
expensive to build dams
reservoir can flood existing settlements
material is deposited in reservoir so farmland downstream can become less fertile
what is channel straightening
meanders are removed by building straighter artificial channels
adv of channel straightening
water is moved out of an area quickly —> reduces flood risk
disadvantages of channel straightening
flooding may happen downstream instead
faster moving water may cause more erosion downstream
what are embankments
raised walls are built along river banks
adv of embankments
river can hold more water so floods less frequent
disadvantages of embankments
expensive and risk of flooding so many break
what are flood relief channels
channels built to divert water around built up areas or divert excess water if river level gets too high
adv of flood relief channels
gates on channels mean that release of water can be controlled reducing flood risk
disadvantages of flood relief channels
increased discharge where relief channel rejoins the river which could cause flooding in that area
what is soft engineering
schemes set up using knowledge of a river and its processes to reduce the effects of flooding
what is flood warnings and preparation
environment agency issues flood warnings through various media (e.g. TV, radio, internet)
buildings are modified to minimise flood damage
residents can prepare sandbags and flood boards prior to floods
advantages of flood warnings and preparation
warnings give ppl time to move possessions upstairs, put sandbags in place or evacuate —> reduces the impact of flooding
disadvantages of flood warnings and preparation
warnings don’t prevent floods
people may not have access to the warnings
modifying buildings is expensive
what is flood plain zoning
restrictions that prevent land use on parts of a flood plain that are likely to be affected by a flood
adv of flood plain zoning
flood risk is reduced —> fewer impermeable surfaces are created (e.g. roads)
impact of flooding is reduced - no buildings to damage
disadvantages of flood plain zoning
expansion of an urban area is limited if there aren’t any other suitable building sites
can’t help in areas with existing buildings
what is planting trees
planting trees increases the interception of rainwater
advantages of planting trees
discharge and flood risk decrease
vegetation reduces soil erosion and provides habitat for wildlife
disadvantages of planting trees
less land available for farming
what is river restoration
making river more natural by removing man made structures so flood plain can flood naturally
advantages of river restoration
discharge is reduced —> less risk of flooding downstream
little maintenance is needed and better habitats for wildlife
disadvantages of river restoration
local flood risk can increase especially if nothing is done to prevent major flooding
why does leeds need a flood management scheme
leeds is located on the floodplain of the river aire
this is a tributary of the river ouse which eventually joins the humber estuary near hull
what was the issue in leeds
on boxing day in 2015, storm eva caused flooding in leeds
environnement agency issued a red warning
how high is the river aire normally and what did it rise to
river aire- 0.9 metres and rose to 2.95m at 1am on the 27th december —> affected the city centre and kirkstall road area
what were the effects of the flood
damage to leeds was £36.8m
3355 properties were damaged (672 being businesses)
what has been done to reduce flooding in leeds
- moveable weirs at crown point in the city centre and further downstream at knostrop (can be lowered to create more room for flood water)
- merging river and canal (removal of 600m stretch of land known as knostrop cut island allowed river and canal to merge) (additional flood capacity for flood water)
- flood walls, glazed panels and embankments stretching more than 4.5km
(raise capacity in times of flood)
social impacts of the river aire management
+ quality of life improved for people with new green areas
+ reduced levels of anxiety as reduced flood risk
economic impacts of the river management scheme (positive and negative)
+ main routes will remain open in flood, reducing disruption for people
+ there are financial benefits by protecting houses and businesses
- cost of the scheme is about £50 million so far and expected to be nearer £100 million when fully completed
environmental impacts of river management scheme
+ moveable weir helps nature —> less flooding so organisms are protected
+ thousands of new trees help the environment through natural flood management
- part of the floodplain will be allowed to deliberately flood in designated areas if river levels are high —> reduce biodiversity
how is a levée formed
- sediment upstream is transported downstream
- when a river floods, the sediment spreads across the floodplain
- largest material is deposited first on the sides of the river bank and the smaller material is deposited further away
- after many floods, the sediment builds up to increase the height of embankments so it can carry more water which reduces flooding
cross section
shape of the river valley
long profile
shape of the gradient
