option A flood mitigation Flashcards
hydrograph elements
rising limb
peak flow/ discharge
lag time
run off curve
base flow
recessional limb
rising limb
-amount of discharge and speed at which its increasing
-(flash flood= very steep)
-generally steep in urbanised catchments
peak discharge
-higher in larger basins
-steep catchments- lower infiltration rates
- flat catchment- high infiltration rates so more through flow and lower peaks.
lag time
-time interval between peak rainfall and peak discharge
-influenced by basin shape, steep, stream order
runoff curve
-relationship between overland flow and throughflow
-low infiltration=high moisture, impremeable surface, strong rainfall, overland flow
base flow
-seepage of groundwater into the channel
-slow movement and main long term supply of river discharge
how does seasonal change impact (river regime)
- amount and nature of precipitation
-seasonal variations in temperature and evapotranspiration
-changes in vegetation cover
variations in rock, soil types and shape and size of basin
recurrence interval
frequency in which events of a certain size occur
catastrophe of flood
high magnitude but low frequency
urbanisation hydrological impact
-shorter lag time
-steeper rising limb
- higher peak flow
-steeper recessional limb
factors influencing flood risks
-precipitation type and intensity
- temperature+
evapotranspiration
-antecendent moisture
-size of basin
drainage density
rock and soil impermeability
-slopes
-vegetation type
-land use
how did urbinization increase flood risk
-creation of impermeable surfaces (roads, roofs, pavements)
-smooth surface served with dense network of drains gutters and underground swerves- increase in drainage density
-natural river channels often constricted by bridge supports or riverside facilities- reduce carrying capacity
impact of urbanisation on lower part of basin
- increased erosion.
- more water getting into rivers
increased speed of flow and transport of materials- enlarged channels
.less erosion due to riverbank protection schemes
deforestation
removal of tress and forest and their ecosystems
deforestation effects of hydrological cycle
-more overland flow leading to more frequent erosion
-rivers transporting more sediment
-reduced evapotranspiration
channel modifications examples and explanations
-channelisation (create new channels)
-enlargement (synthetic levees on preexisting channels so that more water is moved)
-straightening
flood mitigation
examples
-ways of reducing flood risk
dams
afforestation
channel modification
planning
dams
purpose and implications on environment and society
-hold back water during times of flood and release when risk is gone
-benefits to agriculture, energy production (hydroelectric), navigation, recreation, tourism
-increased water loss due to evaporation
-channel erosion downstream
decline in sediments reaching deltas, or ocean.
reservoirs
store excess rainwater in upper drainage basin
afforestation
-flood abatement=decreasing amount of runoff which reduces flood peak
-increase amount of interception and reduce overland flow
planning
planning for floods:
-personal insurance
-being prepared for flooding (sandbags, sealing doors and windows, moving electrical generators)
insurance problem
-people in LIC’s may struggle to get insurance incase of flooding
flood prediction
predicting flood occurrences and strength to prepare for extreme weather events
things to improve flood warnings
-improved rainfall and snow pack estimates
-better river gauging (data collection)
-more current information about human populations and infrastructure
-technology shared among all agencies involved in forecasting and risk assessment
