978-0-00-812422-9 COLLINS CAMBRIDGE AS AND A LEVEL GEOGRAPHY

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storage inice and snowprecipitationon landsurface runoff(overland flow)moisture over landevapotranspirationevaporation from landcondensationprecipitationon oceansoil layerpermeablerock layerimpermeablerock layerpercolationfreshwaterstoragelakethroughflowevaporationlakesurface outflowevaporation from oceanwater tablezone of saturationgroundwater outflowoceanfigure 1.5 The hydrological cycleInputsDrainage basins principally have one main input – precipitation (ppt), whichincludes all forms of rainfall, snow, frost, hail and dew. Water is then storedor transferred in the system for an indeterminate amount of time before itseventual output in the form of evaporation (EVP), evapotranspiration (EVT)and runoff.Precipitation refers to the conversion and transfer of moisture from theatmosphere to the land. Precipitation can be very variable and several factorsmay impact the hydrology of an area: amount and extent of precipitation,intensity, type, duration and geographical distribution.StorageStorage refers to the parts of the system that hold or retain water for periods oftime. They can be open stores on the surface of the land, within vegetation orhidden deep within the rock structure. The amount of time that water is storedfor is dependent on the processes acting on it.Interception refers to water that is caught and stored by vegetation. It isaffected largely by the size and coverage of plants, with large broadleavedtrees catching the most water (in summer). Intercepted water may still transferthrough the system using three main mechanisms:• interception loss – water retained by plants and later lost as evaporation• throughfall and leaf drip – water that is slowed by running off and droppingfrom leaves, twigs and stems• stemflow – water that runs down branches and trunk to the ground.Urban areas and areas that have been cleared for cultivation have much lowerrates of interception.12Hydrology and fluvial geomorphology
transpirationevaporationprecipitationinputoutputinterceptiontransferstemflow/leaf dripstoresurface storagesurface runoff(overland flow)infiltrationvegetationstoragesoil moisturestoragethroughflowchannel storagechannel flowvariable levelpercolationwater tablegroundwaterstoragegroundwater/base flowriver dischargefigure 1.6 Systems diagram – inputs, transfers, stores and outputsWhen vegetation absorbs moisture directly through its root system itbecomes stored within the organism/plant and is called vegetation storage.The amount of water stored relates to the size and variety of plant and the localconditions at any given time. A large leafy and ‘thirsty’ plant will require morethan a well-watered shrub.Surface storage is the name given to any parts of the system where waterlies above the ground on the Earth’s surface. Within a drainage basin watermay naturally accumulate in lakes, ponds and puddles or through humanintervention whereby engineering creates structures to contain water suchas reservoirs and swimming pools. Surface stores have a high potentialevapotranspiration rate as there is a large amount of moisture available withlimited cover.Channel storage refers to water that is contained within a river channel orstream at any given time.Groundwater storage refers to water that has become stored in thepores and spaces of underlying rocks. Despite being hidden, this water isfundamentally important to the hydrological system accounting for almost97 per cent of all freshwater on Earth. Although a significant part of thehydrological cycle, water contained here may be stored for 20 000 years.Any large quantities of water are contained in aquifers. An aquifer isan underground layer of water-bearing permeable rock or unconsolidatedmaterials (gravel, sand, or silt) that can be found at any depth. Those nearestthe surface are often used for water supply and irrigation. Areas that sufferfrom a large extraction of groundwater through wells and pumps require goodrecharge rates (where water stores naturally fill back up). Those areas withlittle recharge consider groundwater to be a non-renewable resource. Manygroundwater reserves are being used at an unsustainable rate too.Groundwater recharge occurs as a result of percolation, infiltration fromprecipitation, leakage and seepage from the banks and beds of water bodies aswell as artificial recharge through from reservoirs and irrigation.In 2013 large freshwater aquifers were discovered under continental shelvesoff Australia, China, North America and South Africa. They contain an estimatedhalf a million cubic kilometres of low salinity water that could be economicallyprocessed into potable (drinkable) water.Hydrology and fluvial geomorphology 13
Page 3 and 4: ContentsIntroductionHow to use this
Page 5 and 6: IntroductionCollins Cambridge A and
Page 7 and 8: 1234567891011121314151617181920Loca
Page 9: figure 1.3 The forested banks of th
Page 13 and 14: amount of water available, vegetati
Page 15 and 16: 0.25Group 10.25Group 50.25Group 90.
Page 17 and 18: Parent materialThe parent material
Page 19 and 20: source is, the higher the gravitati
Page 21 and 22: ErosionThe power of the water and t
Page 23 and 24: Fluvial features: erosionV-shaped v
Page 25 and 26: • The radius of curvature of the
Page 27 and 28: There are three main types of delta
Page 29 and 30: commercial reasons though there are
Page 31 and 32: GroundwaterHuman activity has serio
Page 33 and 34: Event modifications refer to action
Page 35: • Storm drains: Storm drains have

978-0-00-812422-9 COLLINS CAMBRIDGE AS AND A LEVEL GEOGRAPHY

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