[dhafner]

HI,

I am working on my first unsteady flow model and am having major instability problems. I'm trying to model a huge retention basin that collects bank overflows from a nearby the creek.

I'd like to to create a restart file for it, but am not sure if I'm heading in the right direction.

-I've simplified the model, removing all bridges, weirs, and culverts.
-I'm attempting to stabilize the model with an u/s constant flow hydrograph and a d/s high tailwater stage hydrograph that ramps down to a normal tailwater elevation.

I can stabilize the model, but the constant flow is 2500 cfs (the basin will normally be empty) and the computation interval is 30 minutes. When ever I lower the time interval, the model becomes unstable.

What constant flowrate should I probably use in this case where there normally is no flow?

How do I determine if my computation time interval is too high?

Should I stabilize the constant flow model first (minus the structures) before adding the structures back into it? Then attempt to stabilize it again?

Thanks for your patience in reading this. I'm very frustrated and looking for any help to solve these problems.

Thank you.

Dave