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# Reservoirs

A reservoir is an impoundment located on the main channel network of a watershed. No distinction is made between naturally-occurring and man-made structures. The features of an impoundment are shown in Figure 8:1.1.

![Figure 8:1.1: Components of a reservoir with flood water detention features (After Ward and Elliot, 1995).](/files/tHMdRvXIwGMIYMeEDYi3)

        The water balance for a reservoir is:

                $$V=V\_{stored}+V\_{flowin}-V\_{flowout}+V\_{pcp}-V\_{evap}-V\_{seep}$$          8:1.1.1

where $$V$$ is the volume of water in the impoundment at the end of the day (m$$^3$$ H$$*2$$O), $$V*{stored}$$ is the volume of water stored in the water body at the beginning of the day         (m$$^3$$ H$$*2$$O), $$V*{flowin}$$ is the volume of water entering the water body during the day           (m$$^3$$ H$$*2$$O), $$V*{flowout}$$ is the volume of water flowing out of the water body during the day (m$$^3$$ H$$*2$$O), $$V*{pcp}$$ is the volume of precipitation falling on the water body during the day   (m$$^3$$ H$$*2$$O), $$V*{evap}$$ is the volume of water removed from the water body by evaporation during the day (m$$^3$$ H$$*2$$O), and $$V*{seep}$$ is the volume of water lost from the water body by seepage (m$$^3$$ H$$\_2$$O).