2D Model with Internal Connections showing more flow than inflow

[mrae71]

I’m running a 2D model with one 2D flow area and three internal connections that represent a dam, overland flow around the left abutment, and overflow along a watershed divide that runs parallel to the reservoir. I’m using the normal 2D equation for all of the internal connections so I can avoid estimating a weir coefficient, especially for the overflow. When I plot stage and hydrograph for each connection, the total flow for all three connections exceeds what I have going into the model as inflow. The model seems very stable, the hydrographs at the connections are very smooth and the volume accounting shows a very small percent error. I’ve tried running really small cell spacing to really large and have varied the computation interval to as low as 0.3 seconds but can’t get an answer that makes sense. The results at the dam seem okay but it’s primarily the overflow into the next watershed where the flow seems too high. Since I’m using only 2D equations, I don’t believe there’s anything else I can adjust. If I were using weir equations, I would lower the weir coefficient but I was hoping to avoid this.

Any thoughts?

[cameron]

Is the flow going through the internal connections 2D or 3D? If the connections act like a weir, then it may make sense to use the weir equation over the 2D equation. Are you using the diffusion wave or the full momentum solver?

[Anonymous]

The flow over the watershed divide and flow around the left abutment is flow going over high ground so there is not really a defined weir. The dam is definitely a weir. I mistakenly said I was using the 2D equation for all three connections but am using a weir equation with gates at the dam. It’s with the full momentum solver that I get really high flows over the watershed divide and left abutment. I ran the diffusion wave solver first and the results seem very reasonable at all the connections and the flows add up to just slightly less than my inflows.

[Author]

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