The method used to update Load in an E2StorageModel each timestep needed to be modified. The new order was specified by Luis in an email to Dave.

The concentration in the outflow was being calculated before evaporation and infiltration were taken into account.

The relevant code was added April 28 2008.

Luis used the new code in his copy of the trunk to generate a passing test case.

Original message from Luis:
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From: Neumann, Luis (CLW, Highett)
Sent: Friday, 24 July 2009 12:53 PM
To: Penton, Dave (CLW, Black Mountain)
Subject: Storage Test

Dave

As spoken earlier, please find attached the storage test I mentioned about.

The test case is very simple, one catchment with one land use, one storage and one minimal flow from the storage. The rainfall is limited to the first 100 days, then only PET acts on the storage (note that I left rainfall into the storage out to make it simpler).

I am assuming the model intended for the storage was to assume perfect mixing, i.e., the concentration on the outflow should be the same as the storage concentration. However, if one looks at the mass balance, it does not match (see attached spreadsheet).

I think the order of calculation should be:

1 - Add constituent mass from inflows to constituent mass in the storage

2 - Evaporation/rainfall out o/ into the storage

3 - Calculate constituent concentration in the storage

4 - Remove outflows. Outflows should have same concentration of the storage.

5 - Mass in storage is storage concentration * storage volume

6 - Go back to 1 in next time step.

I think at present the order is to do 3 and then do 2, so (assuming no rainfall into storage, only evaporation) the concentration calculated for the storage is lower than it should be, since it is done on a higher volume (uses before evap volume). Than the outflow has a lower concentration than it should be.

I hope this makes sense, if not please do not hesitate to contact me to discuss. It is also possible that the computation at present follows the 1-3-2-4-5-6 order for another reason that I can't see.

Cheers

Luis Neumann