Flashcards in R - Flood management strategies Deck (18):
Why do we do flood management?
The aim of flood management is to protect homes, businesses and the environment from flooding
Why might river basins need to be managed?
-Prevent or reduce the impact of flooding
-Ensure reliable/pollution free water supply
-Avoid conflicts between different land uses eg tourism and farming
What is hard engineering?
Management that involved physical changes to the river - hard engineering defenses are man-made structures that reduce flooding
What is soft engineering?
SE defenses use knowledge of the whole river basin and its processes to try to work with nature
What are examples of hard engineering defenses?
-Dams and reservoirs
-Dredging the channel
-Building flood walls
What are examples of soft engineering defenses?
-Flood warning systems
-Flood plain zoning
-Alteration of urban surfaces
-Weather forecasts and flood warnings
What are the general disadvantages of hard engineering?
-They're expensive to build and maintain - and need technical skill (poorer countries often can't afford these)
-Floods happen less often, but they can be more hazardous if they do happen (eg if a dam breaks meaning a huge load of water will flood the area)
-Natural processes are disrupted, eg crops don't get fertile silt
-Some people think they're ugly (they're an eye sore)
What are the general advantages of soft engineering?
-They're cheaper to maintain (important in poorer countries)
-Flooding is more predictable, reducing the risk of an unexpected disaster
-They can improve opportunities for recreation, eg fishing
-Some people think they're more attractive than hard engineering schemes
H: What are dams and reservoirs? What are the advantages and disadvantages?
A dam is a large wall built across a rivers channel to impede its flow - water builds up behind the dam and forms a reservoir which can then be steadily drained at a controlled rate
-This helps keep discharge downstream of the dam low even during prolonged rainfall
A: -Turbines are often built into the dams which generate electricity (economic benefit)
-The reservoir behind can be used for drinking water/leisure activities
-Steady water release allows for irrigation of land below the dam throughout the year
D: -They're very expensive - they require lots of raw materials eg concrete
-Huge impact on the environment - area where the reservoir goes destroys habitats and forces people out of their homes
-They trap sediment normally carried in the river - this can cause the dam to fail/change the chemical composition of the water behind the am which can kill aquatic animals living upstream/increase erosion downstream as protective sediment has been trapped
H: What is channel straightening? What are the advantages and disadvantages?
This is where meanders are removed by building artificial cut-throughs - this causes the river to take a faster route and flow faster
--This reduces flooding because water drains downstream more quickly and doesn't build up to a point where the river channel can't contain it any more
A: - Reduces the risk of flood by speeding the river up and precenting it from pooling
-It takes less time to navigate the river bc its been made shorter
D: -Downstream of the straightening - flooding is more likely
-Erosion becomes stronger downstream because the river has a lot more kinetic energy
-Altering the river disturbs wildlife q
H: What are Levees? What are the advantages and disadvantages?
Embankments built along rivers - means the river can hold more water without over flooding so it flows less often
--They are much bigger than natural ones and are built out of eg concrete so that they are resistant to erosion
A: They allow the floodplain to be built upon
D: -They encourage development on the floodplain which can increase the risk of flooding
-If they failed they failed, the damage would be far worse than if they didn't exist at all
-They're quite expensive
H: What are Diversion spillways? What are the advantages and disadvantages?
Channels which take water away elsewhere if the water level in the river is too high - water is usually diverted around an important area/to another river
-They prevent flooding because river discharge is reduced
-They generally have floodgates which can be used to control the release of water
D: - An increase in discharge when the diverted water joins another river (or rejoins the same one) could cause flooding below that point
-If spillways are overwhelmed, water will flood areas not used to flooding, which could cause even bigger problems
S: What is flood plain zoning? What are the advantages and disadvantages?
Floodplain zoning involves placing restrictions on land usage in the areas surrounding the river
A: -Damage caused by the river will be greatly reduced
-The floodplain won't be urbanized so infiltration can occur and surface run off is reduces - this reduces the likelihood of the river flooding
-It provides recreational opportunities eg football fields
D: -Limits development in certain areas (problem if there's a housing shortage
-If a floodplain has already been built on, it can't be un-developed without forcing people off the floodplain
S: What is afforestation? What are the advantages and disadvantages?
The planting of trees in a drainage basin to increase interception and storage whilst reducing surface runoff
-This reduces the river discharge so makes it less likely that the river will flood
A: Creates new habitats for animals
-Improves water quality by filtering pollutants out of rainwater
D: Requires a lot of space to be effective
S: What is wetland restoration/conservation? What are the advantages and disadvantages?
This involves creating conditions that are favorable in the development of wetlands
-Wetlands store flood water as well as slow it down (which reduces flooding downstream)
Planting trees and and shrubs along the river bank increases interception, increases lag time and reduces discharge - this also decreases flooding
A: Vegetation protects the surface soil from erosion
-The vegetation provides habitats for wildlife and increases biodiversity
D: There is less land available for farming
S: What is river restoration? What are the advantages and disadvantages?
Involves restoring a river that has undergone hard engineering back to its original course eg un-straightening, removing artificial levees etc
A: It reduces flooding downstream as the rivers discharge is decreased
-Little maintenance is needed (as the river is left in its natural state)
-The river provides a better habitat for wildlife
D: Local flood risk can increase, especially if nothing is done to prevent major flooding
S: What are weather forecasts and flood warnings? What are the advantages and disadvantages?
The Environment Agency monitors weather forecasts, rainfall and river discharge - they warn people about possible flood through TV, radio, newspapers and the internet
A:-This means people can evacuate before the flood happens - saving lives
- people can also move possessions and use sandbags to help reduce damage when flooding occurs
D: -Some people might not be able to access the communication network
-Flash floods may happen too fast for warnings
-People may ignore warnings if they were inaccurate in the past