Posted Mon, 13 Feb 2017 15:13:57 GMT by Lisa
Dear all,

I got a little confused with the signification of the terms of the budget table in relation to my model in transient state.
I am modelling a groundwater system of a sedimentary basin, where the well extractions exceeds the recharge, so that there are decreasing water levels over time and thus, a negative water balance in my conceptual model.

My question is: which term of the Feflow budget displays this water loss?

I thought, the imbalance. But by searching the definition of that term I found different explanations:
- Remaining balance errors due to discretization for example (by pointing on the term) --> it would be a calculation error/model quality check?
- Sum of all the other values, should be close to 0 (residual mass-balance error)
- The Feflow-imbalance corresponds to the sum of all entering and exiting amounts. A positive imbalance implies a gain, i.e. storage in the aquifer under transient condition; conversely a loss in the model domain due to groundwater abstraction or retardation in the aquifer has a negative
imbalance. (phd thesis)

Later on I thought that a negative difference of the term "storage capture/release" would display my negative water balance. But I could not reach a negative difference.

My third idea is, that no term display directly the negative conceptual water balance, so that I´ve to calculate it by myself with the terms:
Border in/out + Well in/out + Surface in/out + storage capture/release = negative conceptual water balance (delta S) and the Feflow-imbalance as quality check.

Thank you in advance for a helping answer!!!

Posted Tue, 14 Feb 2017 11:17:40 GMT by Denim Umeshkumar Anajwala

The definition depends a little bit on the FEFLOW version, which is why you might have found different definitions. In later versions, the storage capture/release has been added to the budget calculation, leaving the imbalance to only reflect a remaining imbalance of all terms above, representing, for example, numerical errors. In your case, the release from storage (POSITIVE value) represents the amount that the storage in the system changes, i. e., the overpumping. The reason that the value is positive is due to the fact that water coming from storage in the model can be seen as a source of water for the model that can leave the model through any of the boundary conditions. Water that is additionally stored in the aquifer, vice versa, can be seen as moving into a 'sink', and consequently is shown as NEGATIVE.

Good luck!
Posted Thu, 16 Feb 2017 08:55:20 GMT by Lisa Krienen Student
Thanks Peter for your reply!

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