ABSTRACT
Rainfall is recorded with a rain gauge (see Figure 2.13) and is measured in millimetres of water. Thus ‘ 1 mm of rain ’ is the amount of water covering any area to a depth of 1 mm. Therefore ‘ 1 mm of rain ’ on one hectare of land is equivalent to 10 m 3 or 10 000 litres of water per hectare (area 10 000 m 2 depth 0.001 m). As rain falls on a dry surface the water either soaks in ( infi ltration) or runs off over the surface as surface run-off . Accumulation of water on the surface (ponding) is a result of infi ltration rates slower than rainfall. Ponding leads to soil capping, which further reduces infi ltration rates. Soil surfaces can be protected with mulches (see p335) and care should be taken with water application rates during irrigation.
