Evaporation

Water losses due to evaporation may be an important part of the water balance for a reservoir, especially in dry or desert environments. If evaporation should be captured, the model must use the Outflow Structures routing method with the elevation-area storage method. An error message will appear if you attempt to model evaporation without using these routing and storage methods. This provides a reservoir surface area with which evaporation can be determined. An evaporation depth is computed for each time interval and then multiplied by the current surface area.

Currently the only evaporation option is the Monthly evaporation method. It can be used to specify a separate evaporation rate for each month of the year, entered as a total depth for the month.

The evaporation depth at timestep $//<![CDATA[ \begin{array}{l}t\end{array} //]]>$, $//<![CDATA[ \begin{array}{l}evap Depth_{t}\end{array} //]]>$, is a function of the current month's evaporation depth $//<![CDATA[ \begin{array}{l}evap Depth_{month}\end{array} //]]>$ and the number of timesteps in the current month, $//<![CDATA[ \begin{array}{l}timesteps_{month}\end{array} //]]>$:

For each timestep, the evaporation volume, evapVol_t, is then calculated as the depth of evaporation evapDepth_t, multiplied by the current surface area, A_t: