Flood management (hard)

Question 1

Dams and reservoirs

Answer 1

+ Can be used to control a river’s discharge. Reservoir as a water store. Can be used for energy etc.
- Without sediment to transfer, river has more energy downstream. Loss of land, displacement of people. E.g. Three Gorges Dam, Yangtze River, China

Question 2

Levees

Answer 2

+ Raising levees effectively increasing the capacity of the channel to hold water, therefore making it less likely that the channel capacity will be exceeded by discharge.
- Will make situation worse downstream if water cannot spill onto floodplain. Mississippi (1993 floods)

Question 3

Dredging

Answer 3

+ Channel able to hold greater volumes of water before it floods.
- Expensive and needs to occur every year. In late1960s, 63 000m3 of sediment dredged from each kilometre of the Mississippi every year

Question 4

Channelisation

Answer 4

+ Alter channel shape to make it more efficient and reduce friction.
- Increase flood risk downstream where faster flow increases erosion (line channel with concrete). The Kissimmee River in Florida has been extensively channelized which has resulted in the loss of wetlands

Question 5

Spillways

Answer 5

Channels to divert floodwater away from urban areas/areas vulnerable to flooding to low impact areas. Bonnet Carré Floodway begins 50km north of New Orleans – diverts excessive water away from Mississippi during times of high discharge through a series of holding reservoirs into Lake Ponchartrain, and eventually into the Gulf of Mexico. This reduces the flood risk to New Orleans and Baton Rouge

Question 6

Channel shortening

Answer 6

Cutting off meander necks to make channel shorter and straighter. Increases gradient so water flushed through system quickly, reducing flood threat. Mississippi shortened by over 300km