Rivers Flashcards
Abrasion
Rocks moving with river wear down river bed and banks
Attrition
Rocks carried by the river collide and break each other into smaller, rounder pieces
Cross Profile
Side to side cross-section of a river channel / valley
Dam / Reservoir
Barrier built across a valley to interrupt a river and create a man-made lake which controls the discharge of the river
Discharge
Quantity of water passing a point in a river in a given amount of time
Embankments
Raised banks along the side of the river, making the channel deeper to hold more water
Estuary
Tidal mouth of a river where it meets the sea - wide banks of deposited mud are exposed at low tide
Flood
River discharge exceeds channel capacity and water spills into floodplains or other areas
Floodplains
Flat area forming valley floor on either side of the river, which is sometimes flooded
Flood Plain Zoning
Organising flood defences in a way that puts buildings away from the floodplains, which may be used for agriculture, playing fields, etc.
Flood Relief Channels
Artificial channels, which carry water away from the main river channel during periods of extreme discharge
Flood Risk
Predicted frequency of floods in an area
Flood Warning
Advance information about when a flood is expected to occur - flood warning systems give people time to evacuate
Fluvial Processes
Processes relating to erosion, transport and deposition by a river
Gorge
Narrow, steep-sided valley, usually caused by the upstream retreat of a waterfall
Hard Engineering
Methods of flood prevention which involve completely artificial structures to reduce or stop river processes leading to floods
Hydraulic Action
The force of the water in the river causes air to get trapped in cracks along the material of the river bank/bed - the pressure gradually wears them away
Hydrograph
A graph which shows the discharge of a river compared to rainfall over a period of time
Interlocking Spurs
A series of ridges projecting out on alternate sides of a valley, which the river winds its course around
Lateral Erosion
Sideways erosion on the river bank on the outside of a meander, causing the river channel to widen and contributing to the formation of floodplains
Levees
Natural embankments of sediment deposited during a flood, which build every time the river floods and which deepen the river channel, so reducing flood risk
Long Profile
The gradient of a river, from its source to its mouth
Meander
A pronounced bend in a river
Ox-bow lake
Arc-shaped lake which has been cut off from a meandering river
Precipitation
Water/moisture falling from the atmosphere e.g., rain, snow
Saltation
Particles bouncing down the river bed
Soft Engineering
Using the natural environment to work with river processes and manage flood risk
Solution
Soluble particles dissolved in the river
Channel Straightening
Removing meanders to make a river straighter to carry water downstream quicker and prevent floods
Suspension
Fine solid material held in the moving water of the river
Traction
Pebbles and stones rolling along the river bed
Vertical Erosion
Downwards erosion, wearing down the river bed and deepening the river channel
Waterfall
Sudden descent of a river over a vertical / steep slope
Erosion
Gradual wearing away and breaking down of the river bank and bed and other solid material in the river
Transport
The movement of eroded material along a river
Deposition
Material settling out of the water when the river flow slows down
Give three factors that affect flood risk
- prolonged/heavy rainfall
- relief of watershed
- geology
- vegetation
- urban land use
Explain how relief can affect flood risk
- shape of watershed determines how quickly water reaches the river
- steep sided is quicker than shallow sided valley
- rounded is fastest
- water reaching river faster; more likely to flood
Explain how geology can affect flood risk
- permeable rocks make it more likely that water will travel as groundflow or throughflow
- reduces surface runoff
- greater lag time, so river less likely to flood
Explain how vegetation can affect flood risk
- trees and other plants intercept water
- slow it down as it tries to reach the river
- increase lag time and reduce flood risk
Explain how urban land use can affect flood risk
- permeable surfaces on the ground (e.g., tarmac)
- water travels mainly as surface runoff, so reaches river quicker
- less lag time, so increased chance of flooding
Describe the location of the River Tees (3 points)
Pennines - North of the UK
Begins near Cross Fell
Ends near Middlesbrough
Roughly 128km long
Explain the formation of waterfalls
- upper/middle course of a river
- river runs over alternating layers of hard and soft rock
- soft rock is eroded faster, leaving a step
- erosion continues and hard rock is undercut; a plunge pool is formed
- overhang gets bigger and eventually falls off, making the waterfall retreat
Explain the formation of gorges
- waterfall is formed from layers of soft and hard rock
- erosion processes create a plunge pool and make it bigger over time
- overhang gradually increases until it falls and the waterfall retreats
- steep-sided valley left where waterfall once was - this is known as a gorge
Explain the formation of interlocking spurs
- upper course of a river
- mainly vertical erosion due to gravity; river cuts down into valley
- bends around hard rock that is difficult to erode
- creates interlocking spurs of land which link together
Explain the formation and development of meanders
- water goes around a bend in the river
- mostly pushed to the outside of the bend, where it moves fastest
- increases erosion due to speed (hydraulic action and abrasion)
- water is slower on inner bend, so some substances can settle out of the water - deposition
Explain the formation of an oxbow lake
- bend/meander in river becomes more pronounced over time
- slower water on inside of bend deposits eroded material
- faster water on outside of bend erodes river banks more
- period of extreme discharge takes place (e.g., rainstorm)
- neck is cut through, and an arc-shaped lake is left behind
Explain the formation of levees
- lower course of a river where flooding occurs
- sediment eroded upstream is transported downstream
- sediment spreads over floodplain during a flood
- largest material on sides of river bank, smaller material further away
- over time, sediment builds up height of the river banks; deeper channel is less likely to flood in the future
Factors leading to deposition
- volume of water decreases
- shallow water
- water moving slower
Drainage Basin
Area of land around a river that is drained by the river and its tributaries
Watershed
Area of high land forming the edge of a river basin
Source
Where a river begins
Mouth
Where a river meets the sea
Confluence
The point at which two rivers meet
Tributary
A small river or stream that joins a larger river
Channel
Where the river flows
Describe the upper course of a river
- often in an upland area; mainly vertical erosion
- river’s load is large, as it hasn’t been eroded yet
- channel is shallow and narrow
Describe the lower course of a river
- land is flatter, due to lateral erosion
- river’s load is mainly fine sediment that has been broken down over time
- channel is wide and deep
Peak Discharge
Maximum amount of water held in the channel
Peak Rainfall
Maximum amount of rainfall (mm)
Lag time
Time taken between peak rainfall and peak discharge
Rising Limb
Shows increase in discharge on a hydrograph
Falling Limb
Shows the return to normal discharge (base flow) on a hydrograph
Base Flow
Normal discharge of the river
Factors influencing lag time
- size of drainage basin
- vegetation
- valley side steepness
- soil type and geology
Evaluate the use of dams and reservoirs in river management
Pros:
- can be used to generate hydroelectric power
- reservoirs can attract tourists
Cons:
- expensive
- trap sediment so may hold less water over time
- habitats flood which can rot vegetation and release methane, a greenhouse gas
- settlements may be lost, displacing people
Evaluate the use of river straightening and dredging in river management
Pros:
- more water held in channel
- reduces flood risk in built-up areas
Cons:
- dredging must be done frequently
- increases flood risk downstream
Evaluate the use of embankments in river management
Pros:
- cheap; one-off cost
- flood water contained within river
Cons:
- looks unnatural
- water speeds up and increases flood risk downstream
Evaluate the use of flood relief channels in river management
Pros:
- removes excess water from channel to reduce flood risk
Cons:
- expensive
- rising water levels may also flood relief channel
Evaluate flood warnings and preparation in river management
Pros:
- time to protect properties
- possessions saved; fewer insurance claims
Cons:
- some people may not have access to the warnings
- may be ineffective with flash floods
- do not stop land flooding
Evaluate the use of flood plain zoning in river management
Pros:
- reduced flood risk for expensive properties
- less damage caused, so fewer insurance claims
- flooded land has other uses e.g., agriculture
Cons:
- not always possible to change existing land uses
- planners must decide what type of flood to plan for
Boscastle flood defence scheme (August 2004)
- £10 million
- widening and deepening river channel
- replacing low bridges with wider ones, to stop them acting like dams (trapped debris in 2004 flood)
- raising car park and using a permeable surface
- tree management - dead trees removed and living ones well-maintained
Alluvium
The sediment deposited by rivers, also known as silt
Mudflat
Sheltered coastal areas where mud is deposited by tides or rivers
Plunge Pool
The pool of water found at the bottom of a waterfall; it is an erosional feature, created by a combination of hydraulic action and the abrasion of the plunging water
River Cliff
Steep bank created on the outside of a river bend by the erosive effect of fast-flowing water undercutting the bank
Slip-off Slope
Gently sloping bank found on the inside of a river bend because of slow-flowing water, depositing sediment
Infiltration
Water that soaks into the ground
Saturated
Unable to contain any more water
Surface Run-off
The water that runs over the surface of the land when the soil is unable to absorb it
