Rivers And Flood Management Book 3 Flashcards
Define a flood
When the amount of water in a channel exceeds the capacity of said channel
Flooding is natural but what can contribute to its magnitude and frequency?
Human activity
What is the name of studying historical records to try to estimate when a dangerous flood will occur?
Flood frequency-magnitude analysis
What can hydrologists use historical records to predict?
Th probability of a flood and the risk of extreme 1 in 100 year floods
What type of floods are more likely to occur in the future?
High discharge floods
Generally speaking, what type of floods occur more frequently?
Lower discharge floods
What is flood magnitude?
The severity of a flood
Why is flood prediction not very reliable?
Much of it is based on historical data
What government agency works in protecting settlements form floods?
The environment agency
What are the physical causes of flooding?
- Excessive prolonged rainfall
- Intense rainfall
- Rapidly melting snow
- Coastal storm surges
What are the human causes of flooding?
- The growth of urban areas
- Deforestation
- Climate change
- Hard engineering
What are the physical impacts of flooding?
- The area of land flooded
- The amount of sediment deposited
- Any change to a river’s course
What are the human impacts of flooding?
- Economic cost- householders+insurance companies
- Economic impact- business+agriculture
- Economic cost of organising help by government and aid agencies
- Social impacts such as deaths, homelessness, displacement of people
- Social impact of health issues
Where do the human impacts of flooding tend to be more severe?
Less developed countries
Why do the human impacts tend to be greater in LEDCs?
Large numbers of deaths, larger numbers of homeless. Contamination of water supplies. Crops can be ruined, potentially leading to a food shortage. Emergency services cannot cope, reliance on foreign assistance
What impacts are most severe in MEDCs?
Economic impacts: insurance claims can be huge, emergency services are trained and equipped well, governments have extra funding to respond in the aftermath of a flood
What does flood management seek to reduce?
The frequency of magnitude of flooding and so limit the damage it causes
Give an example of where even the most sophisticated flood management has failed
On the Mississippi river when it flooded in 1993 and April and May 2011
How did management strategies differ in the more economically developed world and the less economically developed world?
In the MEDW rivers are heavily managed such as the Colorado and Mississippi in the LEDW more limited strategies are used such as on the Ganges in India
Give six examples of hard engineering
Dams, embankments, channelisation, channel enlargement, flood relief channels and flood storage reservoirs
How do dams reduce the risk of flooding?
They are allow water to be stored temporarily in a reservoir and to manage the rate of flow downstream
How do embankments reduce the risk of flooding?
They allow the river channel to carry a greater volume of water
How does channelisation reduce the risk of flooding?
It allows water to pass more rapidly along the channel and can involve cutting off meanders
How does channel enlargement reduce the risk of flooding?
It increases channel efficiency and reduces roughness and can involve dredging and the removal of large boulders from the riverbed
How do flood relief channels reduce the risk of flooding?
They are built when it is too expensive or difficult to modify the existing channel and take excess water around the settlement
How do flood storage reservoirs reduce the risk of flooding?
They allow excess water to be stored and can be and can be used for recreational purposes and example would be in Milton Keynes which has been protected from flooding by the rivers Ouse and Ouzel
Name six soft engineering strategies
Afforestation, agricultural land use management, land use only, wetland and riverbank conservation, river restoration schemes, forecasts and warnings
How does afforestation reduce the risk of flooding?
Planting trees will slow down the rate at which water reaches the river it is a long-term strategy as the trees take some years to mature
How does agricultural land use management reduce the risk of flooding?
Contour ploughing, leaving crop stubble in the ground over winter and strip farming in semi arid areas can help reduce the risk of surface run-off
How does Landuse zoning reduce the risk of flooding?
Not building any residential areas on the land at risk of flooding and leaving the grazing all recreational activity so they can flood when necessary
How does the wetland on the riverbank conservation reduce the risk of flooding?
Natural River channels and their valleys are protected so that habitats and species diversity can be maintained arable land can be returned to former meadowland that can be flooded on a regular basis
How do river restoration schemes lower flood risks?
They return rivers to their original pre-managed states and is more about enhancing the environment and producing flood risk
How can forecast and warnings reduced flood risks?
This allows bodies to immediately give advance warnings and advice on evacuation procedures, in LEDCs such as Bangladesh raised concrete shelters have been built so people can be evacuated to a safe place
