Dear all

Do i have to define storage capacity, initial storage and volume-elevation curve for this resrvoir (man made lake)?

Yes, you do need to define these data. The volume-elevation curve only matters if you want to model evaporation. If not, just give one point for the total storage volume.

One other thing you will need to do is to prevent WEAP from diverting water to fill the reservoir when you do not want to. You can do this with the Maximum Diversion variable.