Hard and Soft engineering Flashcards
Hard engineering involves…
man-made structures that aim to abate natural processes.
Soft engineering involves…
alleviation, so management of the drainage basin, working with natural processes.
Examples of Hard engineering:
-dams, leavees, wing dykes and straightened channels, diversion spillways (flood relief channels).
Hard engineering may cause unexpected…
effects elsewhere in the drainage e.g. increased deposition, loss of habitats.
Levees can be used to…
divert and restrict water flow to value land.
Reservoirs store excess…
rainwater in the upper drainage basin, however, only appropriate in small drainage basins.
Flood-proofing includes any…
adjustments to buildings and their contents that help reduce losses.
Short term flood-proofing:
- blocking up entrance
- sealing doors and windows
- use of sandbags
Long term flood-proofing:
-moving the living spaces above the level of the floodplain e.g. building on stilts.
Land-use zoning and land-use…
planning has been introduced since World War Two.
In the USA, land-use management has been…
effective in protecting new housing developments from 1 in 100-year floods.
Event modification includes…
environmental control and hazard-resitant desing.
Flood abatement involves…
decreasing the amount of runoff, reducing the flood peak in the drainage basin.
Flood abatement:
- afforestation
- reseeding sparsely vegetated areas
- treatment of slopes such as ploughing
- protection from overgrazing, and clear-cutting forests
- clearance of sediment(dredging)
- preservation of natural water-stores
Flood diversion refers to…
the practice of allowing certain areas such as wetlands and floodplains to be flooded to a greater extent.
Reclamation is the process of…
buying land and turning it into the natural habitat and make it a national park.
Reducing loss can be by:
- aid
- increased education and awareness
- bottom-up developments (micro-credit)
Working on prediction involves:
- Plotting gauging stations
- analysing the drainage basin(hydrographs, recurrence intervals)
4 ways of managing floods:
- hard
- soft
- manage the loss
- do nothing and accept the costs
Straightening of the channel:
- maintains discharge
- limits helicoidal flow (flow at different speeds)
- keeps thalweg at the centre
- stops lateral shifting
Artificial Levees:
- stops lateral erosion
- protected floodplain
- increase in CSA, channel capacity and hydraulic radius
Wing dykes:
- build at 90 degrees to the banks
- slower the velocity-deposition
- keeps the river straight-increase in laminar flow
- increased vertical erosion
- thalweg at the centre
Channelisation:
- the channel is covered in concrete
- reduces friction, so higher velocity and discharge
- limits thalweg shifting
- no vertical or lateral erosion
- less turbulence and eddies
Dam:
-controls the discharge all year around
