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61 Cards in this Set
- Front
- Back
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source |
the start of a river, usually in the mountains |
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mouth |
where the river meets the sea |
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tributary |
when small streams join a bigger stream or river |
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drainage basin area |
the area drained by one river and its tributaries |
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watershed |
an area or bridge of land that separates water flowing to different rivers, basins or seas |
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catchment |
area that the water collects from by the water basin |
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drainage density |
the number of rivers that aren't draining only certain catchment area |
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confluence |
the point where rivers meet each other |
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gradient |
the slope of a river |
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long profile |
shows the shape of the river from source to mouth |
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thalweg |
a line connecting the lowest points of successive cross sections along the course of a valley or river |
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channel roughness |
a measure of how rough the bed of a river is; it can be calculated using Manning's Roughness Coefficient |
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channel efficiency |
how efficiently the water moves down the river |
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hydraulic radius |
the shape of the channel is the ratio between the length of the wetted perimeter and the cross-section area |
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wetted perimeter |
the length of the river's bed and banks that is in contrast with the water |
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turbulent flow |
movement of water within a stream that occurs as discrete eddies and vortices; caused by channel typography and friction |
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laminar flow |
movement of water within a stream that occurs as uninterrupted parallel flows; generally occurs in areas where friction is low |
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velocity |
the speed at which the water travels |
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volume |
the amount of water in the river |
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discharge |
the volume of water flowing through a river channel |
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hydrograph |
a graph comparing the amount of rainfall to the discharge of a river (rainfall in bars and discharge in a line) |
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weathering |
the disintegration and decomposition of rocks in situ
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mechanical weathering |
freeze-thaw - water expands 9% when it freezes to form ice salt crystal growth - as crystals grow they exert pressure exfoliation - surface layer flakes off wet/dry - expands when wet and contracts when dry eg. mud granular disintegration - rock crystals expand and contract block disintegration - jointed rocks expand and contract pressure release - weight is taken off the rock |
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chemical weathering |
oxidation - oxygen reacts with minerals like iron (rusts) carbonic acid - rainwater is weak carbonic acid hydrolysis - breakdown of a compound due to reaction with water hydration - minerals take up water and form weaker compounds which dissolves more easily; the expansion can also put physical stress on the rock |
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biological weathering |
mechanical impacts - roots exert pressure chemical impacts - organic acids dissolve |
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factors controlling type and rate of weathering |
climate - heat speeds chemical weathering up, cold favours freeze-thaw, temperature range favours mechanical; moisture is crucial rock type - porosity, chemical composition, crystal make-up, hardness rock structure - beds, joints, faults vegetation - trees do more mechanical weathering than grass but grass holds moisture and organic acids drainage - dry areas suffer less chemical weathering aspect - the direction the sun or rain comes from is crucial rate of erosion - exposes fresh surfaces for weathering human activity - pollution causes acid rain |
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types of mass movement |
slow - creep fast - flows (wet), slides, slumps very fast - avalanche, free fall |
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mass movement |
movement of material under the force of gravity reduces slope angle occurs due to reduction in sheer strength of the slope and/or increase in sheer stress |
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factors controlling type and rate of mass movement |
climate - rain increases weight and lubricates
rock type - soft rocks flow and slide more, eg. clay rock structure - slope of beds is crucial relief - steep slopes mean more movement vegetation - tree roots reduce movement but can cause creep drainage - dry areas suffer less movement aspects - direction of rain is crucial rate of erosion - removes already mass moved material so exposing the slope foot shock from something to trigger it - eg. traffic human activity - making slopes steeper than their stability slope eg. cuttings |
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fluvial processes |
a river's process of erosion or deposition |
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graded profile |
a river's balance between erosion and deposition |
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erosion |
erosion could be from wind, ice, sea, human activity or the river itself; the rate is determined by the energy available and the resistance of the surface; storms and floods increase the rate of erosion
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types of river erosion |
abrasion - load is used to wear away banks/bed
hydraulic action - the force of moving water eroding the land attrition - load collides and grinds away solution - removal of chemical ions, causing the water to dissolve the soft rock over which it flows |
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load |
the sediment carried by a river |
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types of river transport |
floatation - on the surface
traction - rolling along the bed saltation - bouncing along the bed solution - dissolved in the water suspension - held in the water |
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types of river deposits |
bed load - coarse and dropped first; cobbles, then pebbles, then sand suspension - silt and sand solution - rarely dropped unless mixers with salt in the estuary/delta, colours the water |
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alluvium |
a deposit of silt or sand left by flowing flood water in a river valley or delta, typically producing fertile soil |
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the river system |
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channel factors |
channel shape - a smaller wetted perimeter per cross sectional area is more efficient (hydraulic radius) channel size - larger channels are more efficient roughness - the rougher the bed the lower the energy gradient - a flatter gradient creates lower energy load - a heavy load means little spare energy base level - rising base level (usually the sea) means less energy type of flow - turbulent flow uses energy hydrograph - flashy hydrographs (sudden rise in flow) mean more energy |
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basin factors |
hydrological circle/system - size of stores in the system size of basin - larger basins are slower to react shape of basin - narrow long basins react more slowly river network - complex networks slow the flow river density - denser systems slow the flow |
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physical factors |
climate - precipitation type/volume, evaporation, temperature relief - slope, altitude, base level rock type - geology, structure, (faults, beds, tilt of rocks) soil - permeability, thickness, organic content vegetation - type and percentage cover |
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human factors |
water supply - abstraction channel work - dams, weirs, embankments, straightening, widening, deepening, dredging, flood prevention, meander management drainage - of soils, from industries, roads agriculture - crops type, deforestation, irrigation, drainage urbanisation - impervious surfaces, channel controls transport - canalisation, bridges, weirs |
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time factors |
previous weather climatic change tectonic changes |
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bank caving |
turbulent water cutting the river bank |
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upper course features |
interlocking spurs - projectile ridges that extend alternatively from the opposite sides of the wall of a v-shaped valley
waterfalls - a large quantity of water falling over a large drop plunge pool - a deep area at the foot of a waterfall v-shaped valley - a valley formed by flowing water gorges - created by waterfall retreat |
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mid course features |
meanders - bend in the river slip-off slopes - gentle slope on the inside bend of a meander formed by deposition river cliff - created on the outside of a meander bend by the erosive effects of fast flowing water ox-bow lakes - when a meander gets cut off from the main river point bar - depositional feature that accumulates on the inside bend of meanders below the slip-off slope riffles - the ridges often formed of gravel found in the straight parts of a river between two meanders pools - the deep parts of a river located on the outer bend of a meander |
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lower course features |
deltas - formed by deposition in the mouth of the river floodplains - the area of flat land at the side of a river levees - built up banks either side of the river meanders - bend in the river ox-bow lakes - when a meander gets cut off from the main river eyot - a small island it is especially used to refer to river islands such as in the Thames braiding - a river or channel with lots of eyots |
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upper course velocity |
relatively slow moving; despite areas of fast flowing water, large amount of material on the river channel bed means that friction will slow the water down |
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mid course velocity |
the water has increased in speed as the channel widens and becomes smoother; some boulders cause friction to slow it down a little |
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lower course velocity |
the fastest section of the river, as the channel is widest, with very smooth sides, and the greatest volume of water |
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uses of river basins |
power - water mills, hydro-electric (green energy as clean and renewable) industry - fishing, flat land ideal for heavy industry water supply - groundwater (aquifer), reservoirs, water transfer schemes settlement - flat land, pleasant views, water supply services - tourism, recreation, waste disposal minerals - sediments eg. gravel/sand, oil/gas, placer deposits eg. tin agriculture - irrigation, drainage, fertile silts, fish farms transport - ports, bulk cargoes conservation - river meadows, marshlands, nature reserves |
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causes of river flooding |
sudden intense heavy rainfall eg. Worcestershire and Gloucestershire 2007
prolonged heavy rain eg. Lynton and Lynmouth 1952 (heavy rain for 12 days out of 14 in August) sudden seasonal snowmelt eg. UK following heavy snow in 1947 rapid runoff in small basin eg. Boscastle in August 2004 steep slopes cause rapid runoff deforestation so reducing interception and increasing runoff eg. Bangladesh in 2007 increased impermeable surfaces following urbanisation eg. Gloucester in 2007 lambasting dam bursting eg. the Vaiont Dam in Italy 1963 killed 3000 high tide or storm surge backing up water in rivers eg. east coast of England in 1953 and 1978 geophysical events eg. flooding following Mt St Helens eruption in 1980 |
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reasons for preventing floods |
protect population
protect property and farmland safeguard transport avoid costs of floods stop problems elsewhere protect infrastructure eg. transport, power stations conservation (historical and biotic) create jobs |
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methods of prevention: hard engineering
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dams and reservoirs - store water channel enlargement - dredging it wider and/or deeper embankments or levees (or temporary flood walls) flood relief channels - funnel water away shorten river courses - cut off meanders wing dykes - act like groynes and direct water away from banks holding basins - to store flood water in barriers or barrages - eg. Thames Barrier |
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methods of prevention: soft engineering |
marshland - naturally holds and stores water afforestation - especially in Upper catchment areas |
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methods of prevention: planning restrictions |
farming controls - eg. contour planning to reduce run off limits on urbanisation - reduce building on floodplains insist on rainwater harvesting by new buildings - eg. Germany |
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methods of prevention: planned retreat |
flood proofing - eg. buildings with lower floors and electricts; designed to cope with a flood design buildings to float with floods - eg. the Netherlands flood basins - areas allowed to flood to reduce pressure on river channel |
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methods of prevention: behavioural |
flood forecasting - so can prepare and people know the risks flood warnings and evacuation strategies insurance |
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methods of prevention: do nothing |
evacuation emergency planning |
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flood prevention: areas where measures should occur |
floodplain channel upper catchment entire basin channel/valley sides |
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hjulstrom diagram |
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