Temperature - higher temperatures result in more evaporation and less runoff.
Precipitation - heavy showers result in surface runoff, while soft rain results in infiltration.
Rock types - impermeable rocks, eg clay, do not allow water to pass through and the result, therefore, is runoff. Permeable rocks, eg sandstone and limestone, allow water in and, therefore, there is less surface runoff.
The amount of water in the ground - dry ground will absorb more moisture than ground already saturated.
Slope - steep slopes result in runoff and gentle rolling landscape cause infiltration.
In cities there will be more surface runoff because of the nature of the surface. There are a lot of pavements and tarred roads which increase the surface runoff because the water cannot infiltrate the roads.
In these regions there is a lot of vegetation and this increases infiltration into the ground.
It is evident that many factors will influence the amount of runoff or infiltration of a drainage basin. A summary below indicates the influence of the above factors on the drainage density of a river.
|Low density (course texture)||High density (fine texture)|
|Rock type||Porous - water infiltrates into rock||Nonporous - water runs off|
|Vegetation||A lot of plants - roots a bsorb water||No vegetation - water runs off|
|Climate||Soft, intermittent rain - water infiltrates ground||Hard rain - water runs off|