urban drainage Flashcards
why is infiltration low in urban areas
because urban areas are covered in impermeable surfaces such as concrete or tarmac
what is the impact on groundwater of urban areas
low infiltration means replenishment of groundwater is slow
why is precipitation higher in urban areas
due to the UHI effect. this is where surfaces are heated up which creates hot dense air which rises up. convection currents are created and the air cools down and condenses to form precipitartion.
why is is high rates of precipitation bad in urban areas
because ground is impermeable and too much rain can block the drainage systems meaning urban areas often flood.
what effect does urban areas have on the water cycle
there will be large levels of runoff and low infiltration. sloping roofs gutters and roads will direct water into drains which will quickly empty into a stream. so urban areas are more likely to have flooded rivers afetr heavy rainfall. this will reduce groundwater levels.
what are people and urban areas at risk of
flooding
what is catchment management
a holistic way of managing rivers and improving drainage systems by looking at the whole river cathment and the interactions between water and land.
what does catchment management aim to do
minimise issues such as flooding, drought, river pollution and erosion
how can you manage river catchments
hard engineering- dams, floodwalls, reservoirs
soft engineering- land use management (planting trees)
what are some charcteristics of an urban area compared to a rural area
-greater precipitation
-higher runoff
-lower infiltration
-lower evapotranspiration
-less water stored
what does an urban hydrograph look like
it is flashy. this is due to high levels of surface runoff and low levels of infiltration and interception. The lag time of an urban river is shorter due to drainage systems which speed the flow of water through urban areas and a higher peak discharge is evident in urban rivers.
drainage system
Network of underground pipes and rains used to get rid of rainwater in urban areas
guttering
Channels water off buildings and into a drainage system
what is the lag time like in an urban area
Of an urban river is shorter due to drainage systems which speed the flow of water through urban areas
SUDS
sustainable urban drainage system
what are the problems urban drainage faces
flooding and pollution of the envrionment
what are the drawbacks of catchment management
Catchment management schemes are disruptive and expensive. eg construction of the three gorges dam in china flooded 13v citys and 140 towns, displacing 1.2 million people
soft engineering (rivers)
-Afforestation increases interception and reduces throughflow, along with surface runoff. EVT removes water that would eventually end up in the river channel. Afforestation reduces flood risk and water pollution
-Floodplain zoning - restriction on building on certain areas of a floodplain
-Riverbank conservation to reduce lateral bank erosion and collapse through planting to stabilise banks and reduce silting downstream
-River restoration aims to restore the river channel to its original course by removing and reversing past management strategies
-Restoring natural wetlands on floodplains
hard engineering (rivers)
-Dams, floodwalls and reservoirs are built to prevent flooding and ensure a regular supply of water
-River straightening increases the flow of water by increasing the gradient of a river’s channel and removing natural meanders (bends)
-Levees - natural ones can be increased in height to increase bankfull capacity
Embankments can be built or increased using concrete or sustainable materials (usually dredged from channel)
-Diversion spillways also called flood relief channels bypass the main river’s channel during periods of high flood risk. They can also be a permanent feature which act as a wetland, and improve the local environment
