Strand 6 Notes: urban Drainage Flashcards
(13 cards)
Why is urban drainage an issue?
Water quality issues have become increasingly important, due to pollutants from urban areas being washed into rivers or the groundwater.
Issue of an urban river (using the hydrograph)
Tends to be flashy with a short lag time, steep rising & falling limbs so takes a shirt amount of time to respond to the storm/urban river & reach a point of high peak discharge.
What are the challenges of urban drainage
Develop,ent can harm water sources if a traditional approach was adopted, removing water from sites as quickly as possible has a range of impacts (negative).
Problems with hard engineering
Increases urban flooding as a result of using impermeable surfaces. Water can contain pollutants/toxic metals.
What are SUDs?
Sustainabke urban drainage systems a sequence if water management systems/ facilities design to drain surface water in a more sustainable approach than what has been routing run-off through a pipe to a watercourse.
Types of suds
Rain gardens: advantages- flooding protection, water conservation, groundwater recharge. Disadvantages- requires landscaping & management, (not suitable for steep slopes areas), susceptible to flooding if not managed.
Bio-retention areas: advantages- can be planned as landscaping feature & is very effective in removing urban pollutants. Reduced water run off. Disadvantages- requires landscaping & management. Susceptible to clogging.
Wetlands: advantages- good community acceptability, high potential ecological aesthetic & amenity benefits adds value to local property. Disadvantage- land take is high as it requires base flow, not suitable for steep side, vunerabke to high sediment in flows.
Retention ponds: advantages- can cater for all storms, good removal capacity of urban pollutants. High potential ecological aesthetic. Disadvantages- no reduction in runoff volume. Anaerobic conditions can occur without regular inflow. Land take may limit land use in high density sites.
Detention ponds: advantages- caters for a wide range of rainfall events, simple to design/construct, easy maintenance, safe & visible capture of spillages. Disadvantages- requires landscaping management, susceptible to clogging, not for steep sloped areas.
Green roofs: advantages- mimic predevelopment state of hydraulics & hydrology, can be applied in high density developments, improved ajr quality & helps manage UHI impacts. Disadvantages- costly, not appropriate for steel roofs. Maintenance of roof vegetation.
Pervious surfaces: advantages- reduces peak flows to watercourses reducing flooding downstream, reduced effects of pollution in runoff on the environment reduced need for deer excavations. Cost benefits allows dual use of space so no additional land taken. Disadvantages- cannot be used where large sediment loads may be washed/carried onto the surface, risks of long-term clogging.
Issues associated with the management of urban catchment includes wage pollution
Degradation of urban water due to unwanted materials, major pollutants - viruses/runoff. High water temperatures from increased urban air temperatures & discharge waste water can disturb-ecological balance.
Urban precipitation
Urbanisation reduces infiltration through its use of impermeable surfaces (tarmac, concrete) & drains water quickly to the channel. Means lag time is reduced & discharge is increased, shorter lag time in a city.
Urban areas have 5-15% more precipitation than rural areas because warmer air in cities can hold more moisture. Dust & pollution make more condensation.
Urban water mvt
High levels of precipitation would mean more rainfall & flooding in urban areas. Economically, you would have to invest in management schemes.
Interception
Precipitation lands on buildings, vegetation & concrete before it reaches soil.
Vegetation storage
Water taken up by vegetation, all moisture in vegetation at any 1 time.
Surface storage
Total volume of water held in lakes/puddles/ponds
Groundwater storage
Water underground in permeable rock strata,
