Hydrology and fluvial geomorphology 1.4 Flashcards
What are the causes of flooding?
- Heavy rainfall
- Prolonged periods of rainfall
- Impermeable surfaces
- Melting snow or glaciers
What are the main impacts of flooding? EWISE
- Environmental damage
- Wildlife damage
- Infrastructure damage
- Social damage
- Economy damage
In what ways can human activity directly modify drainage basins?
- Altering precipitation: cloud seeding
- Storing water within drainage basins by building dams or groundwater recharge.
- Changing channel characteristics so speed is affected: deepness or straightness.
- Transferring water between basins
- Abstracting water from the river
In what ways can human activity indirectly modify drainage basins?
- Deforestation and afforestations affects a basins flows and stores.
- Changing agricultural land use: changing of impermeable surfaces or vegetation cover.
- Urbanisation decreases permeability of land and increases speed and volume of surface runoff.
What is the flood recurrence interval?
A method of presenting the probability of a flood of a given scale in an area. Estimate is given in years, for example a 100 year flood.
What does amelioration mean?
The act of making something better
How are forecasts and warnings used to prevent flood risk?
- To estimate the level of flood risk.
- Early warnings are important so people can take action.
- The Met Office releases AMBER and RED flood warnings.
What is hard engineering?
Physically altering a river and its channel through building structures or using machinery, usually used to protect surrounding land and property.
What is soft engineering?
The use of natural, sustainable means to reduce flooding, rather than building structures.
Hard engineering: dams
- Built for either water storage or flood prevention.
- It is only if the dam collapses or is controlled safely that water can get through.
- Dams can be expensive, displace settlements and displace wildlife.
Hard engineering: channel straightening
- Where bends and irregularities are removed using machinery.
- They are straightened so that water flows faster and therefore reduces risk of flooding onto floodplains.
- However, this can cause further flooding downstream.
Hard engineering: levees
- As well as being natural, levees can also be reinforced or reconstructed.
- They provide a raised embankment so that water level must increase before flooding.
Hard engineering: diversion spillways
- A constructed channel that allows excess water to flow into when the channel is overflowing.
- On many spillways, there are usually floodgates that control when they are opened and closed.
Soft engineering: floodplain and drainage basin management
- Floodplains provide the space for excess water to infiltrate into the ground.
- It is important to manage them as certain activities can damage them and reduce their effectiveness.
- Agricultural land use is thought to be the most damaging form of land use on a floodplain. E.g. livestock trampling reduces infiltration.
- Agricultural subsides can be used to preserve floodplains.
Soft engineering: wetland and river bank restoration
- Wetlands are ecosystems that are partially submerged in water.
- They are important as they provide somewhere for floodwater to inundate.
- Banning or limiting the drainage of wetlands can help to protect the ecosystem.
- Riverbanks can be restored by protecting and reintroducing vegetation which can limit erosion.
- Ensuring there is no waste so that the river cannot be blocked by a buildof sedimentation.
