Rivers Flashcards
River regime
The variablility of a rivers discharge over the course of a year
Discharge
The amount of water passing a certain point over a period of time
Storm hydrograph
Shows the change in a rivers discharge caused by a period of rain
How do floods occur
Floods occur when discharge exceeds channel capacity
Boscastle 17th August 2004
Brief summary
Rivers Valency, Jordan & Paradise feed into Boscastle
Boscastle built on flood plain
1 months rain in 24 hours
3 million tonnes of water fell onto 40 square kilometre drainage basin
Few trees on side of the valley
Tourist season
Flood management
Reduce lag time and peak discharge
Increase channel capacity
Improve channel efficiency
Hard engineering solutions
Dredging Channel widening/straightening Levees/embankments Dams Outflow storage Flood walls
Soft engineering solutions
Afforestation Floodplain zoning Flood warnings Protection River restoration Wetland & river bank conservation
Natural causes of flooding in Bangsladesh
Onshore winds
In the path of tropical cyclones
Vast drainage basin
Low lying relief
Human causes of flooding in Bangladesh
Population pressure
Urbanisation
Global warming
Impacts of flooding in Bangladesh (1998)
670,000 ha of farmland was destroyed
1000+ human deaths
30,000,000 people made homeless
Dhaka
Capital of Bangladesh
Population of 17,000,000 and growing by 1,500,000 each year
10,000,000 people live in the slums
Cherrapunji
Total annual rainfall is 10980 mm
Total rainfall for May to August is 7560 mm
The LA river, Calfornia
Source in the Simi Hills and Santa Susana Mountains
48 miles long
Managed almost the entire length
Only 2% of water reaches the sea
Management strategies on the LA river
Sediment/debris dam
Flood control basin (dam)
Spreading grounds over permeable rocks
Much of the channel has been straightened and lined with concrete