Subject: Reservoir Calculation (Top of Inactive, Evaporation, Allocation) Posted: 12/9/2020 Viewed: 3923 times
I've created a WEAP-model and have problems understanding some of its results regarding the reservoir. The reservoir has specific values for Top of Inaction, Top of Buffer and max. Storage Volume (=Top of Conservation).
1)The Inactive Zone of a reservoir can only loose water due to evaporation, according to the help guide. And for each time step the previous storage volume will loose or gain Netto-Evaporation and gain Inflow. The result is called Storage for Operation. If the Storage for Operation is higher than the Top of Inactive, Transmission Links will deliver water to demand sites. In my projekt the Storage for Operation ist below Top of Inactive, but the demand site, which has to be allocated water first, still receives up to 20 % of its water demand. Could you point out, if I misunderstood the help guides explanation or if there is special calculation rule that is not mentioned in the help guide?
2)The reservoir looses water due to evaporation or gains water due to direct rain (so the Netto Evaporation is negative or positive). If the reservoir reaches his max. storage in the previous time step, WEAP models no direct rain in the current time step. Could you explain, why upstream inflow creates outflow, but direct rain does not?
3)The reservoir has three demand sites. Each one has its own demand priority. During one time step there is water scarcity. The first demand site can't fullfill its demand, that's why the other other demand sites should receive no water. But the reservoir still deliveres a tiny portion of water (<1% of the demand sites water demand) to the third demand site. Does this error occur because WEAP uses a distribution on a percentage basis for the allocation calculation?
Subject: Re: Reservoir Calculation (Top of Inactive, Evaporation, Allocation) Posted: 12/14/2020 Viewed: 3909 times
"Check the priority for the demand sites."
have you checked base flow?
if you want exact solution send me the model(compressed file)
Ms. Anne Hereford
Subject: Re: Reservoir Calculation (Top of Inactive, Evaporation, Allocation) Posted: 1/6/2021 Viewed: 3833 times
Due to numerical instability issues in the LP solver, very small amounts of water (usually <1 cubic meter per timestep) are sometimes alotted to lower priority demand sites even when higher priority sites are not receiving 100% of their demand. This prevents the solver from reporting infeasibility in later iterations. (Thanks to Jack Sieber for this explanation).
Topic "Reservoir Calculation (Top of Inactive, Evaporation, Allocation)"