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
3 main types of weathering
Physical
Chemical
Biological
Types of physical weathering
Freeze thaw
Pressure release
Insolation/exfoliation
Types of chemical weathering
Salt crystal growth
Hydration
Oxidation
Carbonisation
Types of biological weathering
Plants
Animals
Mass movement
The downward slope movement of earth material
Moves under the influence of gravity
Larger particles need steeper slopes for the effect of gravity to effect the weight of the material
Erosion processes
Hydraulic action Abrasion Attrition Corrosion Cavitation
Landforms of river erosion
Interlocking spurs
Rapids & waterfalls
Evorsion hollows/potholes
V-shaped valleys
Bernoulli effect
Traction (rolling)
Saltation (bouncing)
Suspension (floating)
Solution (dissolved)
Fluvial processes
Erosion
Transportation
Deposition
Deposition
Larger particles are deposited first as more energy is needed to carry them
Hjulström curve
Causes/theories for the formation of meanders
Obstruction
Pools & riffles
Deltas
Large areas of sediment found at the mouth of many large rivers
Positive feedback effect
Sediment supply Bar formation Flow diverted to channel bank Rapid bank erosion Repeat
Eustatic change (eustacy)
Global change in sea level
Isostatic change (isostsacy)
Change in height of land (isostatic recovery)
Paired terracing causes
Climate change
Tectonic uplift
Isostatic recovery/eustatic change
Unpaired terracing causes
Meander migration
Entrenched meanders
Rapid erosion taking place
No time to migrate across, cut straight down
Ingrown meanders
Slow erosion takes place
Endogenetic (internal) factors influencing the weathering of the rock
Presence of certain minerals
Rock texture
Presence of joints and bedding plains
Exogenetic (external) factors influencing the weathering of the rock
Climate and vegetation
Organic acid contained within plants
Presence of water
Atmospheric and soil temperature (2-3 X after per 10 degree temp rise)
Mekong river
One of the world’s richest freshwater fishing grounds
2.6million tonnes of fish a year
