Thiessen polygon Method
In order to achieve accurate estimation of the spatial distribution of rainfall, it is
necessary to use interpolation methods, for th is, the Thiessen* method is considered as
the most important in engineering praxis.
This method assigns weight at each gauge station in propo rtion to the catchment area
that is closest to that gauge.
The method of constructing the polygons implies the following steps:
1. Gauge network is plotted on map of the catchment area of interest.
2. Adjacent stations are connected with lines.
3. Perpendicular bisectors of each line are co nstructed (perpendicular line at the
midpoint of each line connecting two stations)
4. The bisectors are extended and used to form the polygon around each gauge station.
5. Rainfall value for each gauge s