Unit 5: Infiltration and percolation

Question 1

Define the following terms:
1. Infiltration
2. Percolation
3. Infiltration rate
4. Field capacity
5. Infiltration capacity

Answer 1

1. Infiltration - the entry of water into the soil surface.
2. Percolation - the movement of infiltrated water to the zone of saturation at the phreatic zone.
3. Infiltration rate - regarded as the rate at which the water penetrates the soil. If a dry soil is wetted, the infiltration rate is initially high, but it decreases rapidly as the soil is wetted.
4. Field capacity - the point when free water in saturated soil (due to persistent precipitation) can be sustained against gravity, thus no draining take place.
5. Infiltration capacity - the maximum rate at which a given soil can absorb water at a given time.

Question 2

Name the factors that affect infiltration (8)

Answer 2

1. Type of soil
2. Soil structure
3. Exchangeable sodium percentage
4. Slope of the soil surface
5. Initial soil moisture content
6. Vegetation cover
7. Precipitation intensity
8. Depth of water

Question 3

Explain the following cases:
1. Case 1: If rainfall intensity > infiltration capacity
2. Case 2: If rainfall intensity < infiltration capacity

Answer 3

Case 1: If rainfall intensity > infiltration capacity
- ponding takes place
- actual infiltration rate = infiltration capacity, f = fc
- surface runoff occurs

Case 2: If rainfall intensity < infiltration capacity
- all rainfall infiltrates, no ponding
- actual infiltration rate = rainfall intensity, f = i
- no surface runoff