3.2.3.5 Urban drainage Flashcards
built-up areas need to be drained to
remove surface water run-off; traditionally this has been achieved by using underground pipe systems to carry water away as quickly as possible
why are water quality issues become increasingly important?
pollutants from urban areas are being washed into rivers or into the ground and once polluted, groundwater is extremely difficult to clean up
modern approaches such as ____ deliver a more holistic approach to managing surface water and wherever possible mimic natural change
SUDS
why is there such large amounts of run-off in urban areas?
- precipitation falls in greater amounts with greater intensity in urban areas than in surrounding rural areas due to convectional currents created
- natural landscapes like forests and grasslands intercept precipitation and then allow it to infiltrate slowly into the ground reducing run-off
- in contrast, impermeable urban surfaces like roads and rooftops prevent precipitation from infiltrating = most of it remains above the surface where it runs off in unnaturally high amounts
- urban areas also designed to shed water quickly e.g. sloping roofs and cambered roads all
as urban areas are designed to shed water quickly, water is then gathered
- in smooth storm sewers which act like a high density drainage system
- water gathers speed and erosional power as it travels underground
- when the water leaves the storm drains and empties into streams, they fill rapidly
what is a consequence of much of the precipitation being unable to infiltrate impermeable surfaces?
groundwater and soil water levels are reduced; since this is the water that feeds streams during fry periods, base level flows are reduced = urban areas more likely to have flooded rivers after heavy rainfall
the combination of population and urban growth along with predicted increase in the occurrence of severe weather as a result of climate change has meant
many people are now at risk of flooding
while flooding is important when managing catchment in urban areas, it is not the only hing to be taken into consideration by planners:
- pollutants can harm fish and wildlife, kill native vegetation and foul drinking water supplies, and making recreational areas unsafe and unpleasant
- sediment from erosion can fill spaces between rocks on the stream bottom, thus reducing living space for habitat for the biological communities
one way to deal with flood problem is shown by the city of Los Angeles:
- LA channel is designed fail-safe as previous devastating flash flooding led city authorities to convert it from natural and meandering to cement and controller
an alternative to using hard engineering, as seen in LA is a relatively new approach to managing rainfall by using natural processes in the landscape to reduce flooding and control flooding=
SUDS
explain what is involved in a bioswale rain garden (which can form one part of a SUDS system)
- the bioswale rain garden is a sloped retention area designed to capture and convey water while allowing it to infiltrate the ground, therefore reducing flooding by natural means
other examples of components of a SUDS system include:
- roofwater collected in water butts for use in gardens
- permeable block paving used on roads and paths= rain falling onto these surfaces is filtered and stored in the stone below or it flows into grass channels, before it joins the rest of the SUDS system
- detention ponds are located around the settlement which will fill up during heavy rain and store the water, protecting other areas downstream; this water storage in the local landscape provides an attractive place for wildlife and recreation
alot of work has been carried in the USA to implement SUDS systems for example
in Phoenix, Arizona, there is a desert climate which has typical infrequent heavy rainstorms where SUDS can work particularly well in these environments
What’s the urban drainage case study?
Cheonggyecheon River Project, Seoul, South Korea
Seoul is one of the world’s _____ cities
largest along with one of most densely populated
Once central area in the city, Cheonggyecheon was built over
the course of a small seasonal stream and had become overcrowded and blighted by traffic
The South Korean colonial administration had first begun dredging the Cheonggyecheon stream in 1918 aiming to cover it as it was seen as a flood and sanitation risk- what stopped this?
Second world War and Korean war
when was two-year plan scheme launched to restore the river?
2003 where it was transformed into a 5+km of ecologically sensitive green pedestrian corridor
what were reasons for and aims of two-year plan?
- city of Seoul is in the process of changing from a development-orientated urban landscape dependent on the car to one that values the quality of life of its people and the importance of functioning ecosystems
- ageing elevated freeway and concrete deck covering the Cheonggyecheon stream posed safety risks and needed to be repaired and removed
describe the work carried our regarding Cheonggyecheon project
- elevated freeway and deck covering stream dismantled
- over 20 bridges for cars and pedestrians were built to improve movement north-south across the area
- car use discouraged in area and rapid bus lanes added
- to address variable flow of the stream, water from nearby Hanang River is pumped to the area to create a consistent flow; this water is treated to prevent pollution
what were the attitudes and contributions of parties involved in Cheonggyecheon project?
- South Korean president included the restoration of the stream in his successful bid to become Mayor of Seoul in 2001, and it became a priority for his administration
- transportation experts were concerned that removing the elevated highway would increase traffic congestion and chaos in the northern end of the city
- local businesses saw the project as either an interruption or threat to their livelihoods but to minimise any convenience and stimulate business activity, the Seoul Metropolitan Authority:
1- provided extra parking
2- reduced parking fees
3-provided support, subsidies and grants for businesses restructuring along with promoting the local businesses
since the Cheonggyecheon project
- it has become popular with residents and visitors alike for rest and relaxation with stream becoming a major tourist attraction attracting over 20 million visitors since project finished
discuss project’s economic sustainability
- despite its central location, the area has fallen behind the rest of Seoul in terms of economic viability
- since the end of the project, development capital has been invested in residential construction and property prices have risen at double the rates elsewhere in the city
discuss project’s traffic and pollution levels
- speeds in CBD slowed by only approx 10%
- stream sidewalk is an attractive alternative to street-level journeys and so more pedestrian activity in city
- public survey revealed respondents noticed improvements in air and water quality, noise and smells
explain issue of inclusive design regarding project
- design was non-inclusive
- there was limited consideration of certain user groups e.g. elderly and individuals with mobility issues
