1.1 The drainage basin system

Question 1

What are the different outputs?

Answer 1

evaporation
evapotranspiration
channel flow

Question 2

What affects evaporation?

Answer 2

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)

Question 3

What is evapotranspiration?

Answer 3

• 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

Question 4

What is P.EVT?

Answer 4

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

Question 5

What is river discharge?

Answer 5

• 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

Question 5

What are the 5 stores?

Answer 5

Interception
Soil Water : upper levels of soil
Surface water
Groundwater : in pore spaces of rock
Channel storage

Question 6

What is interception?

Answer 6

• 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

Question 7

What causes interception loss to vary?

Answer 7

• surface area: less from grasses than deciduous woodland due to smaller surface area of grass shoots
• density: agricultaral crops interception increases with crop density

Question 8

What is soil water?

Answer 8

• water stored in upper levels of soil and utilised by plants

Question 9

What factors affect soil water store?

Answer 9

• soil depth
• land use management (heavy machinery destroy soil structure)
• soil texture (sand, silt or clay)
• soil structure (large or small pores)

Question 10

What is it and what factors affect surface storage?

Answer 10

water stored in puddles, ponds, lakes etc
- precipitation type
- aquilude - rock cannot hold water
- precipitation duration
- rock permeability
- flat land
- soil texture
- precipitation intensity

Question 11

What is groundwater and what affects it?

Answer 11

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

Question 12

What is channel storage and what factors affect it?

Answer 12

water stored in a river’s channel
- flat land (relief)
- impermeable rocks
- some channels are underground
- abstraction by humans
- rock type

Question 13

What are the different types of above ground flows?

Answer 13

throughfall
stemflow
overland flow
channel flow

Question 14

What are the 5 different types of below ground flows?

Answer 14

infiltration
percolation
throughflow
groundwater
baseflow

Question 15

What is throughfall flow?

Answer 15

• 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

Question 16

What is stem flow?

Answer 16

intercepted water stored on plants and trees flows down a stem onto the ground

Question 17

What is overland flow?

Answer 17

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

Question 18

What is channel flow?

Answer 18

• water that moves through established channels (e.g streams/rivers)
• led by 2 sources: overland flow and groundwater flow

Question 19

What is infiltration and what affects it?

Answer 19

• movement of water from above ground into soil
• permeability of soil
• rate of precipitation
• relief
• saturation levels of soil

Question 20

What is percolation?

Answer 20

slow vertical movement of water into permeable rocks

Question 21

What is through flow?

Answer 21

• through soil that is not saturated and vertically

Question 22

What is groundwater flow?

Answer 22

slow horizontal movement of water under the surface through saturated ground

Question 23

What is baseflow?

Answer 23

• portion of streamflow that comes from groundwater seeping into a river or stream
• no contribution from precipitation

Question 24

What are aquifers?

Answer 24

• underground water stores
• permeable rocks such as sandstone and limestones
• full body of groundwater

Question 25

What is the water table?

Answer 25

• 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

Question 26

What happens if the surface dips below the water table?

Answer 26

• 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

Question 27

What causes groundwater recharge?

Answer 27

• 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

Question 28

What causes losses of groundwater?

Answer 28

• Evapotranspiration:
• natural discharge by seepage into surface water bodies
• groundwater leakage and outflow into adjacent aquifers
• artificial abstraction

Question 29

What is a spring and how do they form?

Answer 29

• 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