Normally, a
catchment will contain multiple rainfall gauge stations. To determine the
characteristics rainfall depth for this catchment, we need to take all of them
into consideration.
We have
three methods to do so. The first one is arithmetical-mean method, which we
simply take the average rainfall depth value from all stations. However, this
method is rarely used.
The second
method is Thiessen-mean method, which we first determine the weightage of each
station based on Thiessen polygon. Then, the weightage is applied to the data
obtained from respective stations.
We may also
use isohyetal method to determine the mean precipitation over a catchment. To do
so, we need to plot the isohyets. The weightage of average rainfall depth
between two adjacent isohyets is calculated by measuring the area in between.
The following shows some examples to calculate mean precipitation using these three methods. Watch the video above for full details.
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