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13 Cards in this Set

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Hydrological Cycle


there are local hydrological cycles:


-Rivers drainage basin is area surrounding river where rain falls on land that flows into river - rivers catchment.


-Boundary of drainage basin is watershed- any precipitation falling beyond watershed enters different drainage basin.


-Draingage basisn are open systems with inputs and outputs.


-Water comes into system as precipitation and leaves via evapouration, transpiration and river discharge.

Inputs- water coming in system




Precipitation includes all ways moisture comes out atmosphere - mainly rain but also snow, hail, dew and frost.

Storage- water stored in system


Interception- precipitation lands on vegetation or other structures-buildings before reach soil.only temp as water evapourates quick.


Vegetation storgae- water being taken by plants. all water contained in plants at one time.


Surface Storage- water in puddles, ponds and lakes.


Groundwater storage- water stored in ground in soil or rocks.


Channel storgae- water held in river or stream channel.

Flows and processes- water moving from one place to another


Surface runoff(overlandflow)- water flowing over the land.


Throughfall- water dripping from one leaf to another.


Stemflow- water running down plants stem or tree trunk.


Throughflow- water moving slowly downhill through soil


Infiltration- water soaking into soil


Percolation- water seeping down into water table.


Groundwater flow-water slowly below watertable through permeable rock.


Baseflow- groundwater flow feeds into rivers through river banks&table.


Interflow- water flowing downhill through permeable rock abover water table.


Channel flow- water flowing in river or stream itself.

Outputs- water leaving system




Evapouration- water turning into water vapour - gas to liquid


Transpiration- evapouration from plant leaves


Evapourtranspiration- process of evapouration and transpiration together.


River Discharge

River Discharge- volume of water flowing in a river


Hydrographs shows river discharge over period of time


1.Peak Discharge- highest point on graph when river discharge at greatest.


2. Lag time- delay between peak rainfall and peak discharge. delay occurs cause takes times for rain to flow into river.


3.Rising Limb- part of graph up to peak discharge


4.Falling Limb- part of graph after peak dishcarge.

Hydrograph affected by:


Rock type- affects lag time & peak discharge. impermeable rock doesnt store water or let it flow through - reduces infiltration and increases surface runoff reducing lag time.


Soil type- affects lag time & peak discharge. sandy soils allow lots infiltration but clay soild have low infiltration rates.


Vegetation- affects lag time & peak discharge. intercepts precipitation &slows movement to river channel, increasing lag time.


Precipitation-affects peak discharge. big storms generate more precipitation.


Tempurature- affects lag time &peak discharge. hot,dry conditions and cold, freezing both result in hard ground. reduces infiltration and increases surface runoff-reducing lag time and increasing peak discharge.

River Processes


Erosion can affect length, depth and width of river.


Energy of river flowing downhill causes erosion. Bed and banks can be eroded making river longer, deeper and wider:


headward erosion- makes river longer.


Vertical erosion-deepens river channels happens in upper course.


Lateral erosion- makes river wider. middle and lower course.





5 ways river erosion happens:


Hydraulic Action- pressure of water breaks rock particles away from bed and banks. strongest in rapids and waterfalls and during floods.


Abrasion(corrasion)- eroded pieces of rock in water scrape and rub against bed and banks removing material. most erosion happens by abrasion.


Attrition- eroded pieces rock smash into eachother and break into smaller fragments. edges get rounded off as rub together. doesnt erode bed and banks.


Cavitation- air bubbles in turbulent stretches of water implode causing shockwaves that break off pieces of bed and banks.


Corrosion(solution)- dissolving of rock by chemical processes.

Velocity of river provides energy needed for it to transport eroded material. Eroded material carried in river called Load and be carried in 4 ways:


Solution- substances can dissolve carried along in water.


Suspension- very fine material like silt and clay particles whipped up by turbulent water. most eroded material is transported this way.


Saltation- larger particles pebbels or gravel too heavy carried in suspension. force of river forces to bounce them.


Traction- very large particles boulders pushed along river bed by force of water.

Deposition is process of droppin eroded material




Happens when river loses energy. when slows loses energy and drops some of load.


Speed and energy of river can be reduced by:


-reduced rainfall causes lower discharge means river slows and has less energy.


-Increased evapouration or abstraction also causes lower discharge.


-Friction


-When river forced to slow loses energy


-Lot engery lost when river meets sea.

Upper stage




Erosion- mainly vertical and by abrasion. Rough channel causes turbulance and large angualr bedload is dragged along river bed causing intense downwards vertical erosion.


Transportation- mainly large particles like boulders carried by traction or saltation during high-energy conditions.


Deposition- little deposition mainly large particles deposited in river bed as engery level drops.

Middle stage




Erosion- mainly lateral and by abrasion.attrition of large particles in stage means sediment particle size decreases from source to mouth.


Transportation- more material carried in suspension as particle size decreases. some large particles moved by saltation.


Deposition- sand and gravel deposited across flood plain as river floods and friction reduces the rivers energy

Lower stage




Erosion- although velocity and discharge are highest theres less erosion cause turbulance is lower and sediment size reducesd. some lateral erosion occurs during forming meanders.


Transportation- smller particles silt and clay carried by suspension or substances carried in solution.


Deposition- smaller particles sand silt clay deposited on flood plain when river floods and in river mouth as sea absorbs river energy.

River landforms-


Waterfalls caused by Fluvial Erosion


Form? when hard meets soft. soft eroded more causing STEP.


water flowing over speeds up due to lack of friction. increase in speed gives water greater erosive power causing further erosion of soft undercutting hard. as hard undercut collapses. deep plunge pool carved by abrasion at foot of waterfall as bits rock collapsed swirled by turbulence. overtime more undercutting causes more collapse. waterfall retreat leaving behind steep-sided gorge.

River landforms-


Potholes caused by fluvial erosion. small circular hollows in bed. formed by abrasion as turbulence swirls rivers bed load in circular motion causing rub and scrap out holes.


Rapids caused by FE relatively steep section of river with turbulent flow where several sections of hard. (bit like mini-waterfalls)

River landforms-


braiding caused by FE. occurs when river carrying vast amount eroded sediment. if velocity drops or sediment too much sediment deposited in channel-causes river divide into small channels eventually re-join to form channel.


floodplains caused by FE. when R overflows banks & floods flat land on side of R there's increase wetted perimeter & reduction in hydraulic radius-increases friction reduce velocity & causing fine silt & sand be deposited across flood plain.

River landforms-


levees- caused by FE.natural raised embankments form as R overflows banks.at flood material deposited across whole flood plain as R loses velocity & energy cause increased friction.heavy material dropped 1st closest to R channel. overtime material build-up on R bank creating levee.


Deltas- caused by FE- when R meets sea energy of R absorbed b slower moving water of sea-causes R deposit load.these deposits buildup on sea bed until alluvium rises above sea level sortof blocking mouth of R

Meanders-


formed by combined erosion and deposition.


form when alternating pools and riffles develop at equal space intervals along stretch of river. as river deeper in pools more efficient so greater energy & erosive power. energy lost as river flows over riffle cause friction.

Rejuvenation


Allows river to resume vertical erosion.R rejuvenated if base level is lowered-caused by ground level rising or drop in sea level.


drop in base level gives river greater potential energy increasing vertical erosion potential.


Long profile of R extended and knick point form and mark junction between original long profile and new one.


landforms associated with Rejuvenation:


River terraces are former floodplains have left above level of present-day flooding following increased vertical erosion.


Incised meanders formed when R keeps meandering course as vertical erosion increased. result is deep, winding valley with steep sides. R left far below level of former floodplain.

Causes of flooding-occurs when discharge of R so high river spills over banks onto flood plain.


major cause prolonged rainfall


Physical factors increasing flood risk- sparse vegetation means little rainfall intercepted so more rain reaches ground. increases volume of water reaching R increasing discharge.


impermeable ground- infiltration cant happen.


high drainage density- have short lag timeslots water flows from streams into R in short space time increases discharge.

Human factors affecting risk of flooding


Urbanisation- area have large areas impermeable concrete so when rains surface runoff very rapid. gutter&drain quick take runoff to R. both reduce lag time so increase discharge.


Deforestation- removing trees&plants reduces interception increases volume of water that reaches channel so increase discharge. D leaves soil loose, soil eroded by rainwater &carried to R raises river bed. reduces channel capacity so takes less water for R to flood.


Climate change- cause increase on rainfall&more storms in some area could increase flooding

Impacts of flooding-


Social- people&animals can be killed, floodwater contaminated with sewerage can lead to lack clean drinking water &put people at rick of diseases, possession damage or lost &people can be made homeless.


Economic- business shut down, rescue work and repairs usually costly insurance goes up, unemployment levels rise, public transport, roads etc destroyed. crops destroyed.


Envrionmental- floodwater contaminated sewage & rubbish, river banjs eroded, river sediment deposited on flood plain. wetlands created.


Hard Engineering Strategies-


dams- huge walls built across R. reservoir behind dam. flood water caught by dam prevents flooding downstream. used for recreational things. expensive, land flooded when reservoir created-destroys farmland and people have to move. affect wildlife.


levees- embankments built along river. hold more water without overflowing. allow floodplain to be built upon it. expensive if L breach rick of server flood.


channel straightening- meanders removed by building cutthroughs. makes water flow faster reduce flood so water doesn't build up. takes less time navigate R as been made shorter. downstream flooding occur, more erosion downstream.

Soft engineering strategies-


Land use management- prevent buildings/roads constructed on floodplain. more water infiltrates so less surface runoff reducing discharge+flooding. recreational use here. restricts development, cant be used in urbanisaed areas.


River restoration- making R more natural. little maintenance needed as R left in natural state. R provides better habitat for wildlife.lcoal flood risk increase if nothing done to prevent major flood.


Alternation of urban surfaces-building porous pavements increases infiltration reducing rapid surface run-off increasing lag time and reducing discharge and flooding. any pollutants filtered out by soil before water reaches channel. expensive.