WQ Model - Problem w/ Dye and Nutrient Mass Balance

Tom or others, I’m continuing my model setup and calibration for Jordan Lake. The hydrodynamic model is calibrated, but I’m having trouble w/ the water quality model. I’m getting inorganic nutrients and chlorophyll-a that are consistently low. Both NOx and PO4 are well below measurements in the lake and the tributaries (about 1/2 of what they should be). To diagnose problem, I tried a case w/ all algal growth set to zero. Nutrients stayed low. Stepping back, I ran the transport model w/ only the dye constituent. I set all surface water inputs to concentration 1.0 and turned off precipitation and evaporation. I used a dye initial condition of 1.0 in every layer of every cell, and ran model for a year. Just like before, the concentrations were all about 1/2 of what they should be (actually more like concentration of 0.6). Looking at the dye concentration contour map it looks as if the model is underestimating dye concentration at the boundaries. I have checked the all the concentration boundary conditions using the 2D X-Y viewer. All the freshwater inputs for creeks and the river look correct, with each dye concentration showing as a constant value of 1.0. For the two outputs (at dam and WTP), the flows look OK, but the temperatures and dye concentrations look odd. The temperature show a constant value of 30 deg C and the dye a constant value of 0.0. I expected them to be time varying at whatever was the calculated depth averaged concentration at the outflow cell. I’m not sure what I can do from here to address the problem. I need to get the dye case working correct before I can go on to do anything more w/ the WQ model. Thanks in advance for any help that you can be provided. I’ve got a zip of the folder that I can send if you want.Thanks, Jim Bowen

Hi Jim,Please attach your model input files and we can take a look.Tom

OK, Tom, thanks, I zipped a folder w/ the dye study test case as I described. The initial condition here is all cells, all layers at 2.0.

Tom, were you able to see any problems w/ the dye test case I sent? We’ve been doing lots of testing on our end. It seems there is some mass loss that appears to occur when cells are “rewetted.” We’ve been able to minimize, but not completely solve the problem w/ some adjustments to the flow input boundary condition I-J, and w/ some adjustments to bottom elevations in those areas. Keeping the area wet seems to help. The mass loss is still there, but it’s now <10%, so we’re moving on w/ what we’ve got. We’re now running dye w/ the WQ model to keep an eye on things w/r to mass loss. The next challenge is linking water column and sediments. More on that in another post.

Looking at your model, you have a constant concentration value for two boundaries, dam out and WTP but the constant flow is equal to 0. EFDC+ will not use these constant concentrations to simulate if constant flow value is 0. If you are using a time series for flow you need to set a time series for concentrations, and only if you are using a constant concentration for flow can you use constant concentrations. You can see more details here:https://eemodelingsystem.atlassian.net/wiki/spaces/EK/pages/240222648/Flow+-+BC