Identify the method that is NOT used for the computation of average rainfall in a catchment having n number of stations.
In order to compute the average rainfall over a basin or catchment area, the rainfall is measured at a number of rain-gauge stations suitably located in the area.
If a basin or catchment area contains more than one rain-gauge station, the computation of average precipitation or rainfall may be done by the following methods:
1. Arithmetic average method.
2. Thiessen polygon method.
3. Isohyetal method.
4. Grid point method