CUE Bk5 - Urban Drainage Flashcards
What % of the global population are in areas where storm intensity, regularity and frequency is a problem?
> 50%
Impacts on urban hydrology (factors below) due to urbanised areas?
1. Total run off
2. Frequency of flooding
3. Peak discharge
4. Seasonal variations
5. Base/normal flow
- Incr > impervious surfaces
- Higher as shorter lag time + incr ‘flashy’ nature
- Higher (seasonal variation) more of a range and change in rural
- Less varied in urban areas (stable), rural more extremes in vegetation
- Limited variation
Hard engineering definition?
Artificial structures to work against natural processes
Soft engineering definition?
Working with natural processes, often seen as a sustainable approach
What are the 4 hard engineering strategies for rivers?
- river straightening
- levees/embankments
- diversion split way (flood relief channels)
- river channelisation
What are the 4 soft engineering strategies for rivers?
- afforestation
- river bank conservation
- flood plain zoning
- river restoration
How does river straightening work as a form of river management?
Straightens river, incr velocity of water and therefore, incr discharge due to less friction
Poor environmental choice
Habitat loss
How does levees/ embankments work as a form of river management?
Incr height of banks and so, water can incr without breaking banks + therefore decreased likelihood of flooding
Incr volume of water can be held at the given points
How does diversion split ways work as a form of river management?
Only used during floods
Open a gate to temporarily hold flood water
How does river channelisation work as a form of river management?
Lining river channels > incr velocity
How does afforestation work as a form of river management?
Planting trees
- incr interception + evaporation
- roots take up water and hold soil in place
How does river bank conservation work as a form of river management?
Planting vegetation along the river > prevents erosion of river banks (lateral)
How does flood plain zoning work as a form of river management?
Low value land use closest to river > allowed to flood naturally e.g. pastures + fields
How does river straightening work as a form of river management?
Allowing it to return to its natural habitat and course
What does SUDS stand for?
Sustainable urban drainage system
What are SUDS?
A sequence of water management practises and facilities designed to drain surface water in a manner that will provide a more sustainable approach than the conventional practise of routing runoff through a pipe to a water source. It is important to deal with both the amount and quality of the water.
What is a bund (or catch pit) linked to SUDS?
A secondary containment system designed to prevent fuel lost from the tank escaping into the environment. Bunds may be constructed from masonry or concrete to contain a single-skin oil storage tank and must be able to hold at least 110% of the tank’s contents should a leak or overpill occur.
What are the 7 key interventions linked to SUDS?
+ brief explanation of what they are
- Permeable surfaces
- Swales (wide shallow drainage channels that are normally dry)
- Bioretention basins (gravel+/or sand filtration layers beneath read beds - store + filter dirty water + improve quality)
- Infiltration trenches (gravel/sand strips)
- Detention basins (holding prongs for storage during floods
- Shallow landscaped depressions planted with flowers + shrubs
- Green roofs
What are swales linked to SUDS?
Wide shallow drainage channels that are normally dry
What are bioretention basins linked to SUDS?
Gravel +/or sand filtration layers beneath read beds - store + filter dirty water > improve water quality
What are infiltration trenches linked to SUDS?
Gravel/sand strips
What are detention basins linked to SUDS?
Holding ponds for storage during floods
What are the 3 types of control?
- source control
- site control
- regional control
Negatives of SUDS? (4)
- Careful selection > could incr spread of pollution > old industrial areas + brown field sites
- Difficult to fit retrospectively
- Has to be small scale due to existing land use
- Potentially high cost
