Soft Management Flashcards
What is soft engineering?
Soft engineering defenses use knowledge of the whole river basin and work alongside nature
Wetland and River bank Conservation What are they? How does it work? Positives? Negatives?
Wetlands can store large quantities of flood water and slow it down , conserving/re-stablishing wetlands gives natural protection from flooding.
Planting trees and shrubs along the river bank (riparian vegetation) increases interception and lag time, reducing discharge. Storm hydrograph becomes more subdued.
Prevents animals/humans walking too close to the river bank, prevents foot erosion
Vegetation provides habitats for wildlife, increasing biodiversity in the area
Roots stablise banks
Intercept pesticides/pollutants
Fertile areas around rivers mean potential high yielding farmland is wasted
Long term strategy- no immediate impact
Euthropication (fertilizers washed into water- encourages algae growth- blocks sunlight- plants/animals in river die)
River Restoration and Afforestation
What are they?
Positives?
Negatives?
River restoration is making the river more natural/return to its original state before management e.g. removing hard management
Afforestation is planting trees in the drainage basin, slows down the rate the water reaches the river, reducing the volume
Floodplains upstream act as a buffer against flooding downstream
Occasional flooding can be beneficial in improving soil fertility
Little maintenance, better habitats/biodiversity
Increased risk of flooding as hard engineering schemes are removed
Alteration of urban surfaces What are they? How does it work? Positives? Negatives?
Sustainable urban drainage systems (SUDS) mimic natural drainage and enable rainwater to drain back into natural systems rather than becoming storm run off contributing to flooding
Building porous pavements or soakaways increase infiltration, reduces surface,lag time increases, less flashy, reducing peak discharge.
Swales and filter strips: vegetated surface features that drain water evenly off impermeable areas
Swales: long, shallow channels
Filter strips: gently sloping areas of vegetated land where run off is directed
Retention ponds: alternates by storing run off at peak flows and releasing at controlled rate
Risk of flooding significantly reduced
Pollutants washed from urban surfaces are less likely to end up in the river as they are filtered out by the soil before reaching the river channel.
Not as effective under extreme rainfall
Land Use management and floodplain zoning What are they? How does it work? Positives? Negatives?
In some areas, planning restrictions are put in place preventing roads and buildings being constructed on the floodplain
Floodplain zoning: certain areas of the floodplain (low value land) are allowed to naturally flood so more economically valuable areas are protected
Contour ploughing: similar to terracing, natural contours marks tilling for soil
Planting and cultivating creating small ridges trapping water reducing overland flow and soil erosion
Strip farming/cropping, closely sown crops (hay/wheat) alternated with strips of row crops (cotton/corn)
Contour ploughing: Cost effective Stops soil erosion by 50% Sustainable Strip farming: Effective in soil and water conservation Reduces surface run off Keeps soil fertile
Floodplain restricted to areas such as parks, playing fields, allotments
May already be a pen urban area present
Contour ploughing: restricted to 15-20 degrees
Farmer has control
Doesn’t help excessive saturation
What is a case study for soft engineering? What management strategy did it use?
River Quaggy, River restoration
General facts about river Quaggy (Location)
17km in length
Passing through Bromley, Greenwich and Lewisham (South east London Boroughs)
Tributary of the river Ravensbourne near Lewisham
What are the reasons for river restoration?
Since 1960’s- river has been heavily managed by artificial channels (increassed channel efficiency and discharge downstream) and culverts
Increased flood risk due to urban development in Lewisham
When did the restoration scheme take place?
2003-2007
What did the scheme involve?
Bringing the river back above ground to its original source
Cutting a new channel through Sutcliffe park, creating a multifunctional open space
The park was lowered and shaped to create a floodplain, floods more easily (purposefully)
What were the social impacts of the scheme?
The parks flood storage capacity of 85,000 m cubed (35 Olympic swimming pools) has reduced the risk of flooding for 600 homes and businesses in Greenwich and Lewisham
Involvement of local community ownership and pride in restoration scheme (Quaggy waterways action group)
What were the Environmental impacts of the scheme?
Created a diverse environment for wildlife, increased biodiversity with the new wetland
Won a natural environment award
New spices e.g. Kingfisher
What were the economic impacts of the scheme?
Much cheaper than hard engineering
What is a negative for river restoration?
Limited space for development in London
