3.2.3.5 urban drainage Flashcards
Why does urban areas have 15-30% more precipitation then rural areas?
more pollution and dust - condensation nuclei - more clouds
warmer air - more moisture
less vegetation - less infiltration / impermeable surfaces
surface and catchment characteristics
Urban - lots of impermeable surfaces and vegetation - less evapotranspiration need for drains
rural is opposite
Impact on drainage basin storage:
River channel:
River dredging : removal of soil underneath to increase depth of rivers
embankment: walks on sides of river increasing its height
Impact on drainage basin storage:
ground water and soil moisture:
Less ground water - more impermable surfaces - less infiltration -more surface run off
Less soil moisture - less vegetation - more impermable surfaces - more drains
Impact on drainage basin storage:
Interception:
less interception - less vegetation - more man made structures
What is a depression storage ?
surface water held in undulations of the land that prevent surface runoff
Impact on drainage basin storage:
Surface storage:
Task 1: Explain how the urban heat island effect impacts reservoirs, lakes and ponds.
Reservoirs, lakes and ponds are all forms of a depression storage. The urban heat island effect is the phenomenon that urban areas have high temperatures that its surrounding rural areas. This impacts reservoirs, lakes and ponds because it increases evaporation which they are vulnerable to.
do urban areas increase or decrease depression storages
more Impermable surfaces - more water held - less infiltration - increase
TASK: State the differences between the natural water cycle and the urban water cycle.
Imported water
Reduced evapotranspiration
Large volumes of poor quality runoff
Reduced infiltration
Wastewater discharge
Explain each part of urban hydrographic
Steep rising limb:
-more impermable surfaces
-less infiltration
-inc in surface runoff
Steep falling limb:
-reduced through flow due to impermable surfaces so water exits through the river channel or another drainage basin
short lag time:
time between peak discharge and peak rainfall is shorter due to steep rising limb (Increased surface run-off, and reduced throughflow due to impermeable of surfaces and drainage)
low base flow:
dec in through flow due to man made impermeable surfaces which dec infiltration
what is catchment management
Catchment Management – The management of urban water and surface water runoff within a given urban drainage basin by looking at the whole river catchment, and the interactions between water and land
aim for suds to minimise
flooding, drought, water pollution and erosion
Explain los angles river channel
One way to deal with the flood problem is shown by the way the city of Los Angeles has managed its river. The Los Angeles River channel is designed to be fail-safe. Devastating flash flooding of the LA River led the city authorities in the 1930s to convert it from natural and meandering to cement and controlled. While directing the river through this built channel has helped control flooding, it has removed the ecosystem services that a river typically provides. In addition, the entire system could be paralysed if one part of the structure sustains significant damage, such as from an earthquake.
what do suds provide?
se SUDS provide ecosystem services, such as climate regulation, flood regulation, water purification and waste management, pollination or pest control.
What are the 6 suds and what do they do?
Bio retention basins: areas of vegitation with gravel to filter dirty water and provide a habitat
swales: attractive ponds to store water and for infiltration and an habitat
greenroofs: dec surface runoff and promotes wild life
infiltration trenches: filter dirty water and promote infiltration
detention ponds: excavated lands that store water incase of flooding
pervious pavements: pavements with porus to allow infiltration
