Inflow into boundary reservoir cell that is initially dry

I am simulating a reservoir with fluctuating water levels and multiple time-varying river inflows using EFDC+ version 8.2 and Sigma-Zed vertical layering with a specified bottom layer and up to 28 vertical layers. I extended the model grid up the rivers to the point where the upper boundary has about 1/2 meter deep water under high reservoir elevation conditions with no inflow, but the bottom elevation of some of these cells is above the initial water surface elevation at time zero, and they would periodically become dry without river inflow. Some river inflows occur into a single boundary EFDC cell, while others have multiple EFDC cells across the channel with varying depths.

In EFDC Explorer, under "Modify/Edit Flow BC Properties", when I use the distribution factors button, in some cases I get the message "No flow factors were set. Either because all cells are dry or their depths are < the wet depth of 0.1 meters". This is a remarkably detailed and helpful error message, by the way, especially when compared to most modeling software.

My questions: 1. Can I have inflow into a boundary cell that could go dry? If so, how best to do it?
2. Given that the flow distribution among boundary cells comprised of multiple cells changes with lake elevation, how can I simulate this?
3. Given that the number of active vertical layers at the boundary changes with time, is there any way to adjust the vertical layers that inflow comes into based on fluctuating reservoir elevations?

Kirk Dean

Hi Kirk,

I understand that there are several cells into the domain that have higher bottom elevation than the initial water surface elevation. It is common that there will be areas that go dry when there is not enough flow in the domain and they become wet again when enough flow gets into domain through boundaries. Here are my suggestions:
1. Try to deepen some of the cells near your most upstream boundary if the bottom elevation is higher than water surface elevation. Another way to handle such scenarios is to run the model for spin up (usually 7 days or so) so that you get good initial conditions for all the cells in your domain. Then use the final water surface elevation from spin up as your initial condition of the model run.
2. If you want to specify flow boundary (i.e., discharge) at multiple cells you would create a boundary group that includes those multiple cells. Then you can assign the flow series for that boundary. Usually that is the measured time series / estimated time series. Then you could click on distribution factors in EE "Modify/Edit Flow BC Properties" and the flows will be distributed based on the size of the cells. The larger cell would be assigned with higher distribution factor.
3. In Sigma Zed, when you have specified the layers for the cells, the number of layers wouldn't change during the simulation. However, the thickness of the layers would change at each time steps to adjust for the fluctuating reservoir elevations.

I hope it answers your questions.

Janesh Devkota

Thank you for your helpful response. My understanding is that the flow distribution factors are calculated on the initial relative size of the cells, and do not change with fluctuating water levels. I was somewhat curious about using the button "apply flow files" on the same tab because it seems like it might be a way to alter the cell distribution of inflow with varying water levels. However, it seems that how that functions is not yet well-described in the existing documentation.

Thanks again

We have added some description to the Knowledge Base for the “Apply Flow files” option here: Please let us know if you have further questions about it.