Flashcards in Rivers and Coasts Deck (43)
A) what are the inputs in a river basin system/hydrological cycle?
A) what are the flows in a river basin system/hydrological cycle?
Channel flow (rivers)
Surface runoff (water flowing overground)
Through flow (water in soil flowing downhill)
Groundwater flow (water in rock flowing downhill)
Infiltration (from ground to soil)
Percolation (from soil to rock)
A) what are the outputs in a river basin system/hydrological cycle?
River flow into the sea
A) where is wate stored in a river basin system/hydrological cycle?
Surface storage (lakes, reservoirs)
Groundwater storage (in soil and rock - rock that holds soil is an aquifer)
Channel storage (held in a river)
A) What are the key features of a storm hydrograph?
Rainfall (shown as bar graph)
Discharge in cumecs = main line graph, discharge: volume of water that flows in a river per second
Rising and falling limb (increase and decrease of discharge)
Lag Time (Delay between peak rainfall and peak discharge)
A) what factors could make a storm hydrograph more dramatic and therefore dangerous?
High/ intense rainfall
Previously wet conditions
B) What are the natural causes of river flooding?
Prolonged rainfall - saturated ground, water can't infiltrate, increases runoff, increases discharge rapidly
Heavy rainfall - lots of runoff, increases discharge quickly
Snowmelt - increases discharge quickly
Relief (I.e. Steep sided valley) - increases runoff, increases discharge quicker
Geology - more prone to flooding if the rock is impermeable because there less percolation, more surface run off
B) What are the human causes of river flooding?
Deforestation - less interception (and therefore evaporation/output), increased discharge. Also causes soil erosion, soil gets washed into river which decreases carrying capacity
Urbanisation - concrete and tarmac are impermeable, increases runoff no increases discharge quickly. Also building on flood plains
What is a tributary?
A smaller river that joins a larger river
What are the types of weathering in a river? Briefly explain
Mechanical - without changing chemical composition (freeze - thaw weathering)
Chemical - by changing the chemical composition (carbonation weathering)
Biological - through living things (plant roots)
What are the four processes of erosion in a river basin? Briefly explain
Hydraulic action - the force of water breaks rock particles away from the river channel
Corrosion - eroded rocks picked up by the river scrape against the channel and wear it away
Attrition - eroded rocks smash into each other and break into smaller fragments
Corrosion - river water dissolves some types of rock like chalk and limestone
What are the four types of transportation?
Traction - large particles are pushed along the river bed
Saltation - pebble-sized particles are bounced along the river bed
Suspension - small particles are carried along by the water
Solution - soluble materials dissolved in the water are carried along
Why/when do rivers deposit material?
If the volume of water falls
If the amount of eroded material in the river increases
If the water is shallower
If the river reaches its mouth
How are waterfalls and gorges formed?
A river flows from hard to soft rock
Soft rock erodes more and a 'step' is created which erodes more so there is a steep drop
The hard rock gets undercut by erosion and it collapses because it is unsupported
The collapsed rocks erode the soft rock at the bottom to create a plunge pool (corrasion)
The waterfall undercuts more so a gorge is created
How are meanders created?
The current on the outside of the bend flows faster because it is deeper (less friction to slow down water so more energy)
More erosion takes place on the outside of the bend to form river cliffs
The slower current on the inside of the bends means eroded materials gets deposited to form slip of slopes
How are oxbow lakes formed?
Erosion causes the outside bends of a meander to get closer
The small area of land as the neck eventually breaks through (often during a flood)
Deposition cuts of the meander and forms an oxbow lake
What are flood plains?
A flood plain is a wide valley floor on either side of a river
The river floods onto the plain and water slows down and deposits material making the flood plain higher
Meanders migrate across the plain, making it wider and the slip off slopes also make it wider
What is a delta?
The deposition from when a river slows down (when meeting the sea/lakes) and doesn't get washed away builds up and blocks the channel so distributaries form. The material builds up more so low areas of flat land are formed.
What are the three types of delta?
Arcuate - rounded shape, lots of distributaries
Cuspate - triangular shape, fewer distributaries
Birds foot - lots of separate parts jut out into the sea
What are dams and reservoirs and what are the advantages and disadvantages of them as flood management?
Reservoirs release water slowly, the water can be used as drinking water or for hydroelectric power, they are also used for recreation. However, dams are expensive and cresting reservoirs can flood existing settlements, eroded material isn't deposited so farmland downstream is less fertile
What is channel straightening and what are the advantages and disadvantages of it as flood management?
Artificial straight channels replace meanders
Water moves out of the area more quickly because it doesn't travel as far but flooding downstream may happen since water is carried there faster
What are man made levees and what are the advantages and disadvantages of them as flood management?
They are man made embankments on either side of the river
They increase the rivers carrying capacity and are quite cheap
If the levees fail it can cause catastrophic flooding
What are flood warnings and what are the advantages and disadvantages of them as flood management?
People are warned about floods by TV, radio, newspaper, and the internet
The impacts are reduced because people move possessions and use sand bags
They don't stop the flood from happening and some people may not have access to the warnings
How can homes and businesses be modified as part of flood management?
People can make plans for what to do in a flood so that the impacts are reduced but it's expensive and doesn't guarantee safety
What is flood plain zoning and what are the advantages and disadvantages of it as flood management?
Restrictions prevent building on parts of flood plains so the risk of flooding is reduced and there are less impermeable surfaces but it means expansion of urban areas is limited and it doesn't help areas that have already been built on.
What are the properties of destructive waves?
They have a high frequency of 10-14 waves per min
They are high and steep
Backwash > smash
Created by string winds and large fetches
What are the three types of mass movement?
Slides - shifting in a straight line
Slumps - shifting with rotation
Rockfalls - shifting vertically
explain longshore drift
The process of material moving along a coastline
1) waves follow the direction of prevailing wind
2) waves hit the coast at an oblique angle
4) swash carries material up the beach
5) backwash carries material back at a right angle
6) the material gradually moves along in zig zags
When does the amount of deposition increase?
Where there is lots of erosion elsewhere and when there's lots of transportation of material into the area and when there is less energy