Inconsistant Results Between DSS and Mapper

[AJ]

I have a storage area connected to a channel via a hydraulic connection (weir). There is a constant inflow to the reservoir of 410 cfs. The results between DSS and profiles cut in RAS Mapper are not consistent. For example, at the constant inflow of 410 cfs DSS shows ~355 cfs (image 1 below), a profile (RAS Mapper) cut in the 2D area right DS of the weir shows about 230 cfs (image 2 below), and another profile cut about 10 ft from the weir shows ~420 cfs (image 3 below). Within 25 ft DS of the weir, the results show 410 cfs.

What could be causing this?

DSS Result:

RAS Mapper Profile at Weir

RAS Mapper Profile ~ 10 DS of Weir

[Lonnie A]

I’ve found profiles in RAS Mapper won’t report flows correctly if there is an internal connector structure within the sampled cell faces. For flow over the weir, get the results from within the geometry editor or look in mapper but a cell or two away from the structure.

[AJ]

Thanks for the response. Why are the result in the “View DSS Data” window different than what is shown in Mapper.

For the same example above, the inflow to the reservoir is 410 cfs. I run the model long enough to reach a steady state and the DSS results show that the weir flow is 355 cfs and the net inflow (to the reservoir) is 55 cfs, Mapper shows 420 cfs up to 100 feet from weir (started looking at mapper results at least 3 cells away form connection and up to 50 cells away) and beyond 100 feet from the weir (more than 50 cells from connection) the result in Mapper is 410 cfs.

Also, the reservoir stage increases to a point and then remains constant. If there is a net inflow of 55 cfs how does the stage remain constant (there is only one outlet and one inflow to the model)? See images below for more detail

DSS Result for Net Inflow and Weir Flow

DSS Result for Stage

[cameron]

What is your time step and grid cell size? Are you using the full momentum or diffusion wave equation?

[AJ]

Overbank grid cell size is 5 ft. Channel grid cells size is 2-4 ft (i used breaklines to orient flow perpendicular to cell faces and to get a finer mesh in the channel up to about 800 ft from the hydraulic structure). The time step is 0.3 seconds. Courant condition showed between 0.2 to 0.4 seconds depending on cell size, I ran it 0.2 and it was not different than 0.3 so I stuck with the larger time step. I used diffusion wave because there is a constant inflow but will try the full momentum option and see if that helps.

[Author]

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