🌆3.2.3.5 - Urban Drainage Flashcards
What is interception?
When precipitation lands on buildings, vegetation, concrete etc before it reaches the soil. Storage is temporary, often quickly evaporated
What is vegetation storage?
All the moisture in vegetation at one time
What is surface storage?
Total volume of water held on Earth’s surface in lakes, ponds and puddles
What is groundwater storage?
Water in underground permeable rock strata
What is channel storage?
Water held in a river or stream channel
How can flooding be increased in urban areas?
If run off from roofs and paved areas is piped into waterways
What are SUDS?
Sustainable Urban Drainage Systems
What do SUDS aim to do?
Control the quality and rate of run off from a development
Improve quality of run off
Enhance the nature conservation, landscape and value of site and surroundings
What are permeable pavements?
Pavements made of porous material such as concrete blocks, porous asphalt and crushed stone
Where does water go from a permeable pavement?
It may infiltrate directly into the subsoil or be stored in an underground reservoir before soaking into the ground
What are swales?
Shallow ditches with gently sloping sides that can be built into the landscape
What are the advantages of swales?
They provide temporary storage for storm water
Reduce peak flows
Facilitate filtration of pollutants
Encourage microbial decomposition
How can green roofs act as SUDS?
They reduce flow rates and improve water quality, as well as improving insulation
What are infiltration trenches?
Stone filled reservoirs to which stormwater run off is redirected
How are pollutants removed from infiltration trenches?
By absorption, filtering and microbial decomposition in the surrounding soil
What does the type of SUDS in place depend on?
The pollutants present in run off
The size of and drainage strategy for the catchment area
The hydrology of the area and infiltration rate of soil
The presence of Groundwater Source Protection Zones or contaminated land
What do SUDS aim to do?
Drain surface water in a manner that will provide a more sustainable approach than what has been standard practice of re-routing run-off through a pipe to a water course
What percentage more precipitation do urban areas receive than rural areas?
5%
Causes for increased levels of precipitation in urban areas
. Urban Heat Island
. Cities produce large amounts of water vapour (industry)
. Less vegetation
. Impermeable surfaces
. Pollution
Causes of increased precipitation: Urban Heat Island
. Increased temperature = increased evapotranspiration
. Warmer air holds more water
Causes of increased precipitation: Less vegetation
. Decreased evapotranspiration = decreased moisture in air
. Decreased infiltration rates
Causes of increased precipitation: Impermeable surfaces
. Water quickly transported (drains and gutters)
. Increased surface runoff causing short lag time and increased peak discharge
Why do impermeable surfaces create issues for local geology
. Rock below doesn’t get water
. Clay goes brittle
. Impacts house foundations
Causes of increased precipitation: Pollution
Increased cloud formation due to more condensation nuclei
Problems with decisions being made by experts when it comes to water management solutions
Residents feel ignored
Feels disruptive i.e. Three Gorges Dam
Issues with traditional methods of urban drainage
. Increased river flow- increased flood risk
. Raw sewage leaks into rivers in high flows
. Road salt, oil, toxic chemicals washes off urban surfaces and enters rivers
. Pet waste = viruses
Why are SUDS considered a better way to manage urban drainage?
. Work with natural environment
. Improve drainage and water quality
. Some methods increase biodiversity as they create new habitats
Swales
. Temporary storm water storage
. Decrease peak flows
. Filter out pollutants
. Increased infiltration
. Installed next to roads instead of curbs
Wetlands and Ponds
. Accommodate water level variation
. Increased flood storage capacity
. Plants and algae filter out pollutants
. Silt traps decrease sedimentation
Permeable Pavements
. Porous pavements i.e. concrete blocks increase infiltration
. Direct infiltration or stored underground
. Removes pollutants in the infiltration process
Infiltration Trenches
. Stone-filled reservoirs
. Runoff directed into them, gradually infiltrates
. Filter strips removes excess solids and pollutants
SUD example
Alcester primary care centre
What SUDs are used
Soakways, swales, raingardens, permeable pairings
What are the benefits of the SUDs
. Environment benefits staff and patiences
. Control of surface runoff
. Water treated biologically through the system
. Biodiversity increases
. Lower cost of installation
Why is precipitation higher in urban areas
. Increased presence of hygroscopic nuclei
. Warmer air in cities can hold more moisture
. There is less vegetation in urban areas and therefore less evapotranspiration
. High surface run off
How much more precipitation do urban areas get than rural areas?
5-10%
Swales
Permeable pavements
Infiltration trench
