Dear Dan :

Couple of items come to mind:

1. You can set the Theta Weighting Factor (in the Boundary Conditions screen) to 0.5. BOSS DAMBRK will then set the Theta Weighting Factor to 0.60 internally, the water surface elevation safety net feature is turned off (allowing the flow to drop below the initial conditions), and the model is then capable of allowing negative flows to occur (flow up the river valley).

2. You can combine the two models into a single model. We have a "super huge" version of BOSS DAMBRK especially compiled for these situations. You can really reduce the time step size and get really accurate models--even for really large models.

Anything else, I'd have to look at the model and troubleshoot it for you.

If you have any additional questions or need any further information, please contact me again.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com