I included a storage area above a 2D flow area to account for lake storage. The lake has a low earthen dam with a 12-inch concrete culvert through it. Outflow is fairly free. The modeled stage and flow hydrograph for the inline structure, between SA and 2D, makes sense, except the culvert flow is a bit switchy – dropping an rising a little. I added headwater/tailwater limits and increased the number of curves for the inline H-tab parameters, but the switchyness remains. I’m guessing it is switching between curves because of inflections in the inflow hydrograph. What is going on?