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3.7.2
Precipitation
Several options of precipitation can be defined. One commonly used precipitation method
is basin average precipitation. With this method, a time distribution can be entered via the
XY Series Editor. Several standard storm distributions can be loaded automatically from
this editor. The standard storm distributions often can not satisfy the user’s requirement.
In this case, distributions can be created by the user directly. An average precipitation is
also input to account for total rainfall.
The basin average method is convenient in small watersheds, where the rainfall can
be regarded as spatially uniform. However, rainfall is normally spatially non-uniform in
large watersheds, where multiple rain gages are used. A gage may be a storm total and/or
temporal distribution recording station type. Recording stations allow for a continuous
rainfall accumulation to be entered. The storm total station only allows for a single
rainfall value for the event. Figure 14 shows a mix use of storm total and temporal
distribution recording station. Gage_A and Gage_B are temporal distribution recording
stations, which are "imaginary" gages and do not participate building the Thiessen
network, which is used in building the rain gage coverage polygons. Gage1 to Gage 10
are storm total stations and they compose a Thiessen network. The temporal distribution
of Gage1 to Gage10 is determined by nearest recording station.
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