What’s Catchment Area

The volume of the river flow or discharge depends on the catchment area and the volume of
rainfall. Figure 1.5-1 shows how the rainfall is divided on both sides (A and B) of the watershed.
For example, there is an existing Hydropower Plant at A-side, the rainfall at B-side cannot be
used for power generation at this Hydropower Plant. Therefore, the catchment area of a
proposed hydropower plant should be known at the first step of the study of hydro scheme.

The dashed-dotted lines in Figure 1.5-2 indicate the watershed of Point-A. The catchment area
is the area enclosed by dashed-dotted lines.

In Figure 1.5-2, the arrows indicate the flows of rainwater. The rainwater in the catchment area
at point A, such as blue arrows in the figure, will eventually flow down through point A, while
the rainwater outside of the catchment area, such as red arrows in the figure, will not pass
through point A.

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