How is water surface elevation computed in the pass-through reservoir/lake routing option?

[igarousi]

Hi there, 

I have a question regarding the lake/reservoir inputs and outputs in WRF-Hydro v5.2. From the inputs (LAKEPARM.nc), the maximum elevation and weir elevation is 582.68 m and 582.47 m, respectively. I expected the model to use one of these values as the initial water elevation level and then keep it constant for the next steps since inflow=outflow in the pass-through routing option. However, that was not right! I checked the simulated water elevation in the outputs. The output shows a constant value of 582.04 m which is smaller than both values above. Could someone please let me know how the model computes this number? Is there a hard-coded factor that applies to either LkMxE or WeirE input values? 

Thanks,

Irene