Fig. 2 shows a cross-section through a hillside catchment area used for farming. The water table and direction of groundwater flow are indicated. (a) State ...

Labelled answer diagram:

(a) The water table defined: [2]

• The water table is the upper level (boundary) of the zone of saturation in the ground. [1]
• Below the water table, all the pore spaces, cracks and gaps in the rock and soil are completely filled with water. Above it, the pore spaces contain both air and water. [1]

(b) Two ways rainwater reaches the underground reservoir: [4]

1. Infiltration: Rainwater soaks into the soil surface through the pore spaces between soil particles. [1] It moves downward through the soil under the influence of gravity until it reaches the water table, where it joins the saturated zone. [1]
2. Percolation: Water that has infiltrated the soil continues to pass through cracks, joints and pore spaces in the underlying rock. [1] It gradually moves deeper until it reaches the porous rock layer (aquifer) that forms the underground reservoir. [1]

(c) How deforestation on the hillside could affect the water table: [4]

1. When trees are removed, transpiration from the hillside is greatly reduced. However, this alone does not increase groundwater recharge because the main effect of losing tree cover is on surface hydrology. [1]
2. Without the tree canopy intercepting rain and roots binding the soil, more rainfall flows rapidly across the bare surface as surface runoff rather than soaking into the ground. [1]
3. With less water infiltrating the soil, there is less percolation down to recharge the groundwater in the aquifer. [1]
4. Over time the water table may fall because the rate of recharge from rainfall is lower than the rate at which water is naturally discharged (through springs) or extracted (through boreholes). [1]

(d) One method to obtain water from the underground reservoir for irrigation: [2]

• Drill or dig a borehole (or well) down through the soil and rock to below the water table. [1]
• Install a pump (hand pump, windmill pump, electric or diesel pump) to bring the groundwater up to the surface, from where it can be distributed to the fields through pipes or channels for irrigation. [1]