river landscapes Flashcards
upper course characteristics
v-shaped valley
steep sides, narrow shallow channel
middle course characteristics
gently sloping sides
wider deeper channel
lower course characteristics
very wide very flat valley and channel
what does vertical erosion do
deepens the river valley and channel
dominant in the upper course
what does lateral erosion do
widens the river valley
dominant in the middle and upper course
what is hydraulic action
force of water pushing air into cracks of the river bed and breaking pieces off
what is abrasion
eroded rock picked up by the river scrape and rub against the channel wearing it away
what is attrition
eroded rocks that crash into eachother break into smaller pieces
what is solution
river water dissolves some types of rock eg chalk or limestone
what is traction
large rocks are pushed along the river bed by force of water
what is saltation
pebble sized particles are bounced along the river bed by the force of water
what is suspension
small particles are carried along b the water
what is solution ( transportation)
soluble materials dissolve in the water and are carried along
how is a waterfall created
- water flows over an area of hard rock then an area of softer rock
- river erodes the softer rock quicker forming a step
- hydraulic action erodes the step further forming a PLUNGE POOL and undercuts the hard rocks
- eventually the undercut leaves no support for the harder rock so it falls into the plunge pool
- the broken rock erode the softer rock and deepens the plunge pool
- this process repeats and the waterfall moves further up the stream leaving a steep sided gorge
formation of a meander
- current is faster on the outside of the bend
- more erosion takes place here
- current is slower on the inside bend
- more deposition occurs here forming slip off slopes
formation of an ox bow lake
- erosion causes the two outside bends to get closer
- meander neck gets narrower
- eventually the river breaks through the land and cuts across the neck
- deposition cuts off the meander forming an oxbow lake
what is hard engineering
man made structures to control the flow of rivers and reduce flooding
what is a dam and a resevior
dams are barriers built across the river
reservoirs is an artificial lake formed behind a dam
advantages of dams and resevoirs
- store water, control water flow and prevent floods downstream
- used to generate hydroelectric power
disadvantages of dams and reservoirs
- very expensive to build
- creating a reservoir can cause flooding in existing settlements
- material is deposited in the reservoir so farmland downstream can become less fertile
what is channel straightening
meanders are removed by building straighter artificial channels
advantages to channel straightening
water leaves the area more quickly so it reduces a flood risk
disadvantages to channel straightening
flooding may happen downstream instead
faster moving water can cause more erosion downstream
what is flood relief channel
channels are built to divert water around built up areas or to divert excess water if water levels get too high
advantages to flood relief channel
gates on the channel means that release of water can be controlled
disadvantages to flood relief channel
increased discharge where the relief channel rejoins the river which could cause flooding
what is soft engineering
schemes set up using the knowledge of a river to reduce the effects of flooding
what are flood warnings and preparatrion
flood warnings are issued through radio tv and internet
buildings are modified to minimise damage
residents can prepare sandbags and flood boards before
advantages to flood warnings and preparation
warnings give people time to move possessions put sandbags in place or evacuate
minimises impact of flood
disadvantages to flood warnings and preparation
- warnings dont prevent floods
- modifying buildings are expensive
- doent guarantee safety
what is flood plain zoning
restrictions prevent buildings on parts of a flood plain that are likely to flood
advantages to flood plain zoning
- flood risk is reduced
- impact is reduced, no buildings to damage less money spent
disadvantages to flood plain zoning
expansion of an urban area is limited if there arent any other suitable building sites
what is planting trees
planting trees in the river valley increases the interception of rainwater
advantages to planting trees
vegetation reduces soil erosion and provides a habitat for wildlife
disadvantages to planting trees
less land is available for farming
