Dear Kester,
I use EFDC Explorer to model the flow in a reservoir. Now I have a
problem in the modeling and would like to ask for your advice.
The initial water level may be low (e.g. 190m) and the water level for
outflow from spillway (e.g. 240m) may be high. I specify the inflow
boundary conditions at the locations where the inflowing rivers
joining the reservoir at elevation 240m and the outflow boundary
conditions at the spillway at elevation 240m.
Normally I cannot make EFDC to run in this case. It looks like in this
case there is a dry region between the inflow boundary points and the
water body region. I am not sure how to make EFDC to work in this
situation.
On the other hand, if I choose to specify the boundary conditions at
the locations where the inflowing rivers joining the reservoir at
elevation 190m, then the problem is how I can take into account the
bathymetry region as the water level rises from 190m to 240m?
The reservoir has a bowl shape and the bottom elevation is the lowest
in the middle and the elevation is higher on the rim of the bowl.
Thanks very much for your advice!
Best regards,
Albert
Hi Albert,
Thank for your interesting question.
It seems that your inflow boundary locations become dry because the initial water level is smaller than the bottom elevation. In this case, the model might not work. To avoid this problem, you can lowering your bottom elevation at the boundary cells or you can move this inflow boundary locations to further upstream of river where we can ensure those cells is always in wet conditions.
I hope this can solve your problems, if not, please send us your model and we can check it in details. My email is: nxtinh@ds-intl.biz
Thank you
// Tinh
Dear Tinh,
Thanks very much for your message.
I understand your point now. The key thing is to make sure that the boundary conditions are specified at locations or cells that are wet.
I have a specific question regarding this issue. That is how to specify the boundary conditions at the locations that move with time? In my case, when the water comes into reservoir and the water level is rising, the boundary cells are moving accordingly. Indeed I can specify the boundary conditions at the boundary cells when the water level is low, but when the water level rises the boundary cells move as well. I will then need to update the boundary conditions at the boundary cells at the new water level.
I am not sure how to make this work in EE. If possible, could you please give me directions for this?
Thanks again for your assistance!
Kind regards,
Albert
Dear Albert,
Thank for your question again.
In reality, when you have a river flow into a reservoir then that river should be always wet unless you have completely no discharge coming in. Therefore, the boundary cells should not become dry during your simulation time. I assuming that you assigned all river cross-section cells as your river inflow boundary, right? If so, you can choose only some cells at the center of river or some cells at deep water depth to assign for the incoming boundary. By doing this, I think it will not affect to your model simulation results.
Hope this helps.
Cheers,
// Tinh
Dear Tinh,
I have a specific question regarding the specification of Boundary Conditions in EE6.
Under “Boundary” and “Edit/Review” we may open a dialog box “Modify/Edit BC Properties”. In this “Modify/Edit BC Properties” dialog box and under “Flow Parameters for Entire Boundary Group” there is a button called “Apply Flow Files”.
When I click on this “Apply Flow Files” button, there is a section called “Build Time Varying Boundary Flows with Wetting and Drying Cells” and I have to provide a Flow File and a Rating File.
I have read the Manual but unfortunately I didn’t find sufficient details. Could you please explain it to me what the Flow File and Rating File are and what this “Build Time Varying Boundary Flows with Wetting and Drying Cells” is used for?
I suspect but am not so sure that this section would be useful when the inflow/outflow boundary conditions are specified at locations that vary with time. It would be beneficial if you could give me an example for the use of this function.
Again, thanks so much for your assistance!
Kind regards,
Albert
This function is designed to be used when modeling a wide river with a flood plain. In normal flow conditions all the flow is in the main channel; however in an extreme event it is necessary to distribute the flow over into the flood plain. The Flow file is the time series of total flow in the river. The rating curve is used to tell EE what flow corresponds to what elevation. As flow increases the dry cells in the flood plain become wet. As the flow decreases the cells go dry and water into the cells stops. Used in this way every cell will have its own time series as the flow is distributed across all the cells.