urban drainage Flashcards
(18 cards)
what Is urban drainage
a collection of water management practices that aim to be sustainable and quick to reduce flooding
why do urban areas have up to 15% more precipitation than rural areas
warming of the ground causes convectional uplift of the air
dust and pollution make more condensation nuclei
what are some key factors that might affect the drainage of precipitation in urban areas (urban hydrology)
urban areas have more impermeable surfaces e,g roads preventing precipitation from infiltrating
less vegetation
urban areas have designs to shed water quickly e.g sloping roofs, water gathers in storm sewer systems which act like drainage systems
what is a flood/storm hydrograph
shows how a river discharge response to storm events
what is discharge
the amount of water In a river flowing past a particular point expressed as cumecs
what is lag time
the time between the peak rainfall and peak discharge
what is a flashy hydrograph
short lag time and steep rising limb
urwhy are urban areas more likely to have a flashy hydrogrsaph
impermeable surfaces and lack of vegetation
lack on interception
rainfall hits ground at speed so surface runoff is promoted
what is a drainage basin
the area of land drained by a river
what are some ways that urban areas can alter water storage in a drainage basin
when urban rivers are manages they are dredged, embankments are built and rivers and channelized to increase storage capacity
more depression storage such as surface puddles because of impermeable surfaces
what is hard engineering
man made, expensive
have high impact on the landscape
unsustainable
an example of hard engineering in an urban area
river channellisation
straigenting river using concrete so it travels faster
course of the river can be altered diverting flood waters away from settlements
what is soft engineering
less expensive
sustainable
less impact on the environment
an example of soft engineering in an urban area
afforestation
trees are planted near to a river, greater interception
flood plain zoning
policies to control urban development close or on the floodplain
what are examples of SUDs
rain gardens- small depressions in the ground that act as infiltration points
bioretention basins- grave/sand filtration layers beneath reed beds
naturalised swales- wide shallow drainage channels
green roofs
how can suds affect the shape of a flood/ storm hydrograph
peak discharge is significantly lower
what are the benefits of Suds
reduce the risk of flooding by slowing down the speed of surface runoff
create green spaces in urban areas
environmentally attractive
require little to no energy
case study of a river restoration case study
castle Orwell urban wetland
see sheet
