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Inflows vs Tribs and Outflows vs Withdrawls

Mon, 04/21/2003 - 10:48am — Wally
I have a few unresolved issues in terms of exactly how to set up my model. I'm trying to model a lake (1 branch) with two tribs and one outlet -- should be easy right? The outlet is a weir of known height and i have daily outlet flow data. Right now i have the outlet flow data in the QOT file, but it doesn't affect the model (i.e. the lake level keeps rising even when the outflow values are highly exageratted). My question is should i be modeling the outlet as an outflow (and if so how do i turn it on) or should i try modeling it as a withdrawl? I have pretty much the same question with the tribs... do i want to make the trib coming into Seg #2 the inflow? - or is it ok to leave it as a trib? thanx Wally[addsig]
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Hydrodynamics
Thu, 04/24/2003 - 12:56pm — Tom

Wally, You should be modeling the outlet as a structure. If you turn on the snapshot output, you can make certain that what you think you are telling the model is indeed what it is seeing in terms of outflow. Keep in mind that very small errors in inflow/outflow can result in very large discrepancies between observed and computed water surface elevations. This is oftentimes a function of whether or not you have interpolation turned ON or OFF, but even errors of <1% in inflow/outflow measurements can result in very large water surface elevation discrepancies. You can specify a tritbutary as inflow to segment 2, but realize that the momentum associated with the flow will not be accounted for. In cases like this where boundary conditions can be handled several ways, I always try all the options out to see if they have an impact on the results. If they do, I always chose the more realistic method. Tom[addsig]