Hydrosphere

Question 1

Explain how human activities can impact on the

hydrological cycle.

Answer 1

Possible answers might include:
For deforestation:
The cutting down of trees increases run-off and the potential for soil erosion.
(1 mark)
 Decreases in evapo-transpiration and therefore cloud formation impacts on
local rainfall patterns. (1 mark)
 Changes to vegetation cover can lead to more extreme river flows as water
is not intercepted and stored by the trees. (1 mark)
For irrigation:
 Taking water from a river or ground water storage can reduce river flow.
(1 mark)
 Lowering water tables and increasing evaporation/evapo-transpiration by
placing water in surface stores, eg ditches/canals. (1 mark)
 Increased farming opportunities provided by irrigating crops removes water from the hydrological cycle as the crops grow. (1 mark)
For urbanisation:
 The removal of natural vegetation and replacement with impermeable
concrete/hard surfaces and drains (1 mark) can speed up overland flow and
can lead to higher river levels. (1 mark)
 As more urban land is concreted over the rate of evaporation from these
surfaces increases as the rate of percolation through the land surface
decreases. (1 mark). It also decreases the amount of water which returns to
groundwater storage, possibly reducing the water table. (1 mark)
For mining:
 The silting up of lakes, rivers and reservoirs leads to reduced storage capacity
in these areas. (1 mark)
 Mining may also lead to reduced vegetation cover leading to increased run-off
(1 mark), higher evaporation and cloud formation altering the rainfall
pattern. (1 mark)

Question 2

10. Account for the differences in discharge between the urban and rural hydrographs.

Answer 2

The lag time is shorter in the urban hydrograph as impermeable surfaces e.g. tarmac lead to rapid surface run-off via drains and sewers resulting in quick transfer of water to the river. Water management systems in urban areas move water quickly into the river and sewers leading to a steep rising limb. In rural area interception by vegetation acts as a store for rainfall, delaying the transfer of water to the river and leading to a longer lag time. Infiltration is greater in rural areas, resulting in transfer via groundwater flow. This process slows the journey of rainfall into the river, resulting in a shallower recession limb. Percolation and groundwater storage are common in rural areas with permeable surface. This leads to a slow release of water in the hours, and even days, after a rain storm which delays the return of rivers in rural areas to normal levels (base flow). The slow transfer of water results in a lower peak discharge in rural areas.

Question 3

9. Explain how two factors affect a storm hydrograph (4)

Answer 3

The size of the drainage basin has an effect as large basins will have high peak discharges because they catch more precipitation. Larger basins have longer lag times than small basins because the water takes longer to reach the rivers. Basins with steep slopes will have a high peak discharge and a short lag time because the water can travel faster downhill. Permeable rocks and soils e.g. sandy soils, absorb water easily allowing water to travel slowly through the soil, reducing peak discharge as well as increasing the lag time in a river. Impermeable soils e.g. clay soils, are more closely packed together so water can’t infiltrate, therefore, water reaches the river more quickly reducing lag time. Vegetation intercepts precipitation and slows the movement of water into river channels which increases lag time. Water is also lost due to evaporation and transpiration from the vegetation and this reduces the peak discharge of a river