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shallow river

Fri, 01/24/2003 - 4:39pm — jamesnoren
Hi, I'm having trouble getting CE-Qual-W2 to run on a 3/4-mile reach of river that has a slope of .001. The river is on average 40 ft wide and less than 2 ft deep. Can CE-Qual-w2 work on such a river? Thanks, Jim[addsig]
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Hydrodynamics
Sat, 02/15/2003 - 12:58am — Scott

Jim It runs fine on such systems. But be careful of initial water surface elevations and flow rates though. Also, you may have to limit the DLTMAX for numerical stability. Scott[addsig]
Tue, 02/25/2003 - 9:52am — jamesnoren

After getting the model running on the upper half of the river, I have added a reservoir downstream. My problem now is that the reservoir has a hydrodam where the upstream water level is 14 meters above the downstream pool. The model won't run using a spillway between the two waterbodies because of negative surface layer thickness downstream using minimum timestep at iteration 0. Also, pre.wrn states Water surface elevation difference of14.00 m between segment 44and segment 41. I'm wondering is a spillway is the correct structure to use and if it's not acceptable to have a large vertical drop between waterbodies. Thanks, Jim [addsig]
Thu, 02/27/2003 - 1:04am — Scott

Jim The hydrodam is no problem. Make sure each branch are separate waterbodies - these then have independent vertical grids. Then insert a spillway for the end of the river branch and direct that flow into the upstream segment of the reservoir. In this way you can have a 14 m head difference between branches. One point, set the DHS of the river =0 (a flow BC - set the flow file =0 m3/s) and the UHS of the reservoir as =0 (also a flow BC, also set this dummy file with a flow=0). Then set up a spillway linking these 2 segments. It should work fine. Scott[addsig]
Thu, 02/27/2003 - 8:37am — jamesnoren

Thanks Scott, Yesterday I tried linking the DHS and the UHS between waterbodies with dam flow, and that seemed to work. In my case Br 4 DHS (-44) and Br 5 UHS (-41). Is damflow an acceptable alternative to your suggestion?[addsig]
Sat, 03/01/2003 - 8:11pm — Scott

Jim My suggestion may be 'cleaner' based on how I set up the code linkage - but the way you did it may also work - you would know immediately if it didn't work. Since you set up each linkage with negative #'s and there is no outflow file for each, then I guess that will work. It will rely on your spillway/weir linkage for doing the flow correctly... Let me know if you have any problems with how you set it up... Scott[addsig]
Wed, 03/12/2003 - 3:09pm — jamesnoren

Scott, The model is now up and running and I have begun the process of calibrating. Do you have any general suggestions for speeding up the run times? Should I mess with the number of layers or layer heights in the bathymetry files? Thanks, Jim[addsig]
Mon, 03/17/2003 - 1:18am — Scott

Jim Unfortuantely, unsteady river flow is stable only at low time steps. If you have more layers you can better simulate the channel shape and velocity profile, but if the river is well-mixed vertically, you could get away with less layers. Alternatively you could buy the latest PC and get a speed boost. We are actively now looking at ways to reduce the run times of river systems. Many others I know run a VERY coarse grid for a river model to get the water quality etc calibrated in the ball-park. Then, refine the grid and finish up the calibration. What are your longitudinal and vertical grid spacing and averge time steps? Scott[addsig]