Subject: Reservoir Evaporation Posted: 11/12/2014 Viewed: 18635 times
I have en counted a problem of some calculations regarding water balance.
According to the literature that i have followed evaporation of small tank can be calculated as follows
multiplying the surface area of the reservoir by evaporation loss

But the problem is, the calculated value (by myself ) is not match with the results generated by the WEAP
Therefore could you please explain the formula and the methodology that is used to calculate evaporation

Other thing is that we calculate reservoir storage/ volume as 0.4*Surface Area of the Tank*Depth

In WEAP we have to provide "Volume Elevation curve" but not the "Area Elevation curve". In order to calculate the the Resevoir Surface Area they have to use the above mentioned curve. Does the formula use to calculate the volume of the tank by WEAP is similar to the above.

Mr. Jack Sieber

Subject: Re: Reservoir Evaporation Posted: 11/12/2014 Viewed: 18627 times
All the equations are documented in the WEAP User Guide, which is available online. For reservoir evaporation, see http://www.weap21.org/WebHelp/River_Reservoir_Flows.htm

The reservoir evaporation rate is specified in WEAP as a change in elevation. Using the Volume-Elevation curve, a change in elevation can be translated into a change in volume to get the volume lost to evaporation. This is done by a simple linear interpretation between adjacent points on the volume-elevation curve.