1.1 The drainage basin system Flashcards
What are the different outputs?
evaporation
evapotranspiration
channel flow
What affects evaporation?
Meteorological factors:
temperature, humidity and windspeed
- other factors e.g amount of water available, vegetation cover and colour of the surface (albedo or reflectivity of surface)
What is evapotranspiration?
- combined effects of evaporation and transpiration
- evaporation = when water heated by the sun, so becomes a gas and rise into atmosphere
- transpiration : occurs in plants when they respire through their leaves. releasing water they absorb through their roots, which then evaporates
What is P.EVT?
Potential evapotranspiration
- main difference between actual evapotranspiration is moisture availability
- P.EVT is water loss which would occur with unlimited supply of water in the soil for use by the vegetation
What is river discharge?
- volume of water passing through a cross sectional point of the river at any one point in time
- unit = cubic metres per second (Cumecs)
- water leaves the basin through streams which drain basin
What are the 5 stores?
Interception
Soil Water : upper levels of soil
Surface water
Groundwater : in pore spaces of rock
Channel storage
What is interception?
- water caught/stored by vegetation
3 main components:
canopy interception - water caught by leaves/branches of trees
stemflow - water that runs down the stems/trunks of plants
litter interception - water trapped by the leaf litter and other organic debris on the forest floor
What causes interception loss to vary?
- surface area: less from grasses than deciduous woodland due to smaller surface area of grass shoots
- density: agricultaral crops interception increases with crop density
What is soil water?
- water stored in upper levels of soil and utilised by plants
What factors affect soil water store?
- soil depth
- land use management (heavy machinery destroy soil structure)
- soil texture (sand, silt or clay)
- soil structure (large or small pores)
What is it and what factors affect surface storage?
water stored in puddles, ponds, lakes etc
- precipitation type
- aquilude - rock cannot hold water
- precipitation duration
- rock permeability
- flat land
- soil texture
- precipitation intensity
What is groundwater and what affects it?
water stored in pore spaces of rock or lower soil
- aquifers (water bearing rocks)
- rock permeability (permeable rocks = more underground storage)
- soil depth
- land use management
- soil structure (large or small pores)
- time of year
What is channel storage and what factors affect it?
water stored in a river’s channel
- flat land (relief)
- impermeable rocks
- some channels are underground
- abstraction by humans
- rock type
What are the different types of above ground flows?
throughfall
stemflow
overland flow
channel flow
What are the 5 different types of below ground flows?
infiltration
percolation
throughflow
groundwater
baseflow
What is throughfall flow?
- water flows from leaves/foliage onto ground
- prominent in areas with large canopy that receives lots of rainfall e.g rainforest
- but will occur whenever precipitation falls onto plants/trees
What is stem flow?
intercepted water stored on plants and trees flows down a stem onto the ground
What is overland flow?
water flows above ground as sheetflow (lots of water flowing over large area) or on rills (small channels unlikely to carry water when no rainfall)
- will occur when water cannot infiltrate the soil
What is channel flow?
- water that moves through established channels (e.g streams/rivers)
- led by 2 sources: overland flow and groundwater flow
What is infiltration and what affects it?
- movement of water from above ground into soil
- permeability of soil
- rate of precipitation
- relief
- saturation levels of soil
What is percolation?
slow vertical movement of water into permeable rocks
What is through flow?
- through soil that is not saturated and vertically
What is groundwater flow?
slow horizontal movement of water under the surface through saturated ground
What is baseflow?
- portion of streamflow that comes from groundwater seeping into a river or stream
- no contribution from precipitation
What are aquifers?
- underground water stores
- permeable rocks such as sandstone and limestones
- full body of groundwater
What is the water table?
- level at which the pore spaces and fractures in the ground become saturated
- above water table is unsaturated soil and below water table is saturated soil
What happens if the surface dips below the water table?
- groundwater will fill the surface space to become surface water
- if surface water dries up, groundwater will continue to replenish area underneath water table
- water table can rise/fall and surface water will rise/fall accordingly
What causes groundwater recharge?
- infiltration of precipitation until it reaches groundwater
- seepage through banks and bed of surface water such as rivers
- groundwater leakage and inflow from adjacent rocks and aquifers
- artificial recharge from irrigation, reservoirs etc
What causes losses of groundwater?
- Evapotranspiration:
- natural discharge by seepage into surface water bodies
- groundwater leakage and outflow into adjacent aquifers
- artificial abstraction
What is a spring and how do they form?
- they form when groundwater that is stored underground finds a way to reach the surface
- it can happen when there’s a crack or opening in the Earth’s surface, allowing the water to flow out and form a spring
