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67 Cards in this Set
- Front
- Back
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What are some different ways to reduce flood risk
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Channelisation
Flood storage reservation Dams Afforestation Levées ........... |
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What is channelisation
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Straightening, deepening and widening the river so its efficiency and capacity increases. Concrete banks are used to minimise erosion
BUT the by straightening the river, the problem is just moved further downstream |
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What is a reservoir?
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Where water is stored, it stops the water going over land and minimises amount of water downstream
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What is a dam?
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A reservoir to store and control the water. Water is held back by the dam, and released in a controlled way
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What landforms are created by a meander and where?
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A river cliff on outside of meander
A point bar on inside of meander |
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Features of the inside of a meander?
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Slower velocity
Deposition Shallower water Point bar |
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Features of the outside of a meander
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Fastest flow
Lateral erosion Deepest water- thalweg River cliff Undercutting |
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What are riffles?
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Riffles are SHALLOWER, FASTER sections of water
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What are pools?
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Pools are DEEPER, SLOWER sections of the water
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How are River Cliffs created?
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On the outer bend of the meander, current is faster, causing HYDRAULIC ACTION + CORROSION to erode outer bend and create the River Cliff
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How is the Point Bar created?
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The eroded material from outer bend, is TRANSPORTED by HELICOIDAL movement and DEPOSITED on inner bend to form the Point Bar
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How are meanders created?
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Eventually pools MIGRATE to OPPOSITE sides of the river
Riffles are found in STRAIGHTER sections of the channel This causes river to become SINUOUS |
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What is Isostatic Change?
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When there are local changes to level of land (sea level changes due to height of land changing) EG lce Age caused land to sink slightly so sea level appears to rise slightly
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What is Eustatic Change?
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When the sea level rises or falls globally. EG global warming, global cooling, melting glaciers, Ice age (when the ice melts)
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What is Rejuvenation and what does it do?
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Rejuvenation is when there is a FALL IN SL in relation to land level
Or a RISE IN LAND relative to Sea Rejuvenation lets river RENEW its energy and its CAPACITY TO ERODE as POTENTIAL ENERGY is increased |
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What land forms are created by rejuvenation?
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Knick points, river terraces and incised meanders
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What is the Competence of the river
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The largest sized particle a river can contain at any one moment of time
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What is the Capacity of a river
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The ideal amount of debris a river can carry at any one moment of time
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What is a 'Grade'?
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The idealised long profile of a river ie if the energy was balanced along a river's course and river was able to carry all of its load
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What is a Knick point?
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Marked break or change in slope of a long profile of a river due to rejuvenation
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Would an efficient river have a large or small wetted perimeter?
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Low
Because less contact with banks and bed= less friction |
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How to calculate hydraulic radius, and what it shows?
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HR= cross section area/wetted perimeter
The higher the value, the more efficient the river |
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What is Discharge measured in?
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Cumecs, m^3/sec
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What factors affect the speed of the river?
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Weight of water PE
Height above base level PE Steepness of channel KE |
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What is so special about clay?
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It needs a lot of energy to get started as it is cohesive and flocculates
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What causes a drop in river's energy?
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Increase in volume of load (eg landslide)
Decrease in rainfall Flood in the river Shallow water (inside meander) Decrease in gradient |
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Name the 4 processes of Erosion
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Attrition, abrasion, hydraulic action, solution
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Attrition
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When the pebbles knock together and become smaller and rounder
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Abrasion
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Material carried by the river wears away the bed and banks, causing vertical and lateral erosion
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Hydraulic Action
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Frictional drag and pressure created by the moving water forces the air bubbles into crack in the banks and can collapse and weaken rocks
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Solution
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Water in channel is slightly acidic so it can dissolve the bed and banks
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What are the 4 different types of River Transportation?
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Suspension, dissolved load, bedlock traction, bedlock saltation
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Suspension
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Tiny particles remain suspended in the water
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Dissolved load
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The products of solution are carried by the river
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Saltation
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Particles are too large to be suspended and may be lifted and dropped till they gradually move downstream
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Traction
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When river flows fast, large stones may slide with aid of smaller stones
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How are Waterfalls created?
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EROSION
Harder, resistant sediment on surface and softer sediment below. Soft sediment erodes creating plunge pool due to abrasion and attrition Then creates hangover- because hard sediment doesn't erode Collapses to create a gorge |
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What is the name of the sands and clays deposited on a river floodplain?
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Alluvium
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How are Interlocking Spurs created?
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EROSION
Occurs in upper course where there is more vertical erosion As the river erodes the landscape, it winds and bends to avoid areas of hard rock Creating the interlocking spurs |
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How are Ox-bow lakes created?
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EROSION and DEPOSITION
When there's high discharge, higher velocity=more erosion on outer bend of meander, making the neck smaller and smaller Meanwhile former channel is cut off by deposition |
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How are Incised Meanders created?
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EROSION
Rejuvenation SL decreases/land level increases more vertical erosion, river becomes deeper The meanders that are usually in the LC and further up due to rejuvenation (because river stays at same level, but SL has decreased/LL has increased) River erodes more vertically to try to reach equilibruim |
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How are Rapids formed?
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EROSION
Resistant rock on top, softer rock below Water flows over resistant rock, cuts through softer rock As the resistant rock ins't eroded, this creates a bump, and when the water goes over the bump it becomes more turbulent and creates white stretches of water |
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How are Pot Holes created?
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EROSION
Pebbles in river bed get trapped in slight hollows on river They're drilled deeper into the holes by turbulent action of river Abrasion enlarges hole Attrition inside hole creates smooth pothole |
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Where are Pot Holes found in the river?
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Usually in Middle Course- Rougher river bed, more sediment
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How are River Terraces created?
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EROSION
Vertical erosion occurs on a former floodplain Where it renews its downcutting, its new channel sinks into the former floodplain So old floodlplain is above level of present river |
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How are Floodplains created?
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EROSION and DEPOSITION
river reaches bankfull stage and spills over onto flat adjacent land |
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How are Levees created?
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DEPOSITION
River overflows its banks Increase in friction due to contact with floodplain creates loss in velocity and more deposition The heavier sediment settles closer to the channel and finer materials travel further |
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How are Deltas created?
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DEPOSITION
They are at the mouth of river by sea The velocity decreases at the mouth so bedload and suspended material is deposited Fresh water mixes with sea water and clay and it flocculates Clay settles on river bed |
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What must there be for deltas to be created?
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Rate of deposition must be higher than rate of sediment removal
Sediment load must be large Sea must have small tidal range and weak currents |
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What types of deposit are Deltas usually composed of?
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Larger particles deposit first to form TOPSET beds
Medium particles travel further to form FORESET beds Finest particles travel furtherest and form BOTTOMSET beds |
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What different shapes of Deltas are there?
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ACUTE- dendritic pattern. Lots of tributaries- causes braiding. Smooth outline
BIRDS FOOT- Few river channels lead to sea. Elongated CUSPATE- Material is spread out evenly on either side of channel. Pointed like a cup ESTURAINE- Funnel shape. Tidal and river forces |
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How is braiding created?
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Different discharge
Little water in channel More deposition/ increase in sediment/ decrease in gradient |
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Characteristics of where Deltas are found
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Lower, flatter land
Little vegetation Low energgy Low tidal range Lots of sediment |
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Stores in hydrological system
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Groundwater store
Lakes Reservoirs Soil storage Rocks Puddles Surface storage |
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Transfers/flows in hydrological system
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Throughflow
Infiltration Percolation Overland flow Base flow |
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What are the 4 stages of the Water Budget?
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Soil moisture recharge
Soil moisture surplus Soil moisture utilisation Soil moisture defecit |
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What factors can affect Storm Hydrograph?
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Size and shape of drainage basin
Drainage density Steepness of slope Duration and intensity of rainfall Type of precipitation Permeability of rock Vegetation cover Urbanisation Deforestation |
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What would permeable rocks do to the storm hydrograph
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Permeable rocks can ABSORB more water
So there is longer lag time Higher peak discharge |
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Describe and explain the uses of a hjulstrom curve
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It shows the ability of the river to erode, transport and deposit materials. This is affected by the efficiency, discharge and thus the capacity and competence of the flow.
It is useful in showing the minimum velocity needed to pick up a certain sized particle, through the critical erosion velocity. And the Maximum velocity a river can be flowing before it deposits its load, critical deposition velocity |
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What is the difference between long and cross profiles?
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Long profiles look at the rivers length. Cross profiles look at the shape of the river channel
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Discharge
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Volume of water
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Velocity
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The speed it travels
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What affects the discharge of a river?
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Drainage density- tributaries
Soil type Rock type Relief- steepness of slope Antecedent rainfall Dams Urbanisation |
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How does potential energy and kinetic energy change the development of a valley profile?
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PE occurs in a valley profile near the top of the river by the source. This is because it is high up so has the most gravitational energy
The PE is then converted to KE when it is flowing downstream KE can be used in several ways- eg turbulence and friction uses up KE, converting it to heat energy |
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Evaluate hard schemes of protection
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Gorges- 3 gorges dam. Bad because 1.4 million relocated. Destroyed cultural monuments. Pollution. Destroyed habitats of animals- white flag dolphin. £25 bn to build
Schemes like channelisation can reduce flood risk in a certain area, but just moves the flooding downstream. Artificial Raising river banks- water unable to enter river after flooding |
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Evaluate soft schemes of protection
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Afforestation- good but the trees will take years to grow. So good for the future. But not an immediate solution
Forecasting and preparation, warning systems Flood land use zoning |
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Comparing MEDC flood effects to LEDC
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Cumbria Bangladesh
MEDC- cost £100 million, but paid for by the government 2 killed Power supplies cut iff LEDC- cost 10% of the GDP. People lost half their income 1000 killed Millions left homeless and were unable to repair damage |
