I'm trying to model subcritical flow in an open channel with a side weir of certain small length at the middle of the main channel, so a certain amount of fluid discharges through the weir. I need to match the two parameters - Froude number and flow depth just at the beginning of the side weir with experimentally measured values. I tried modelling with upstream depth of water and velocity corresponding to required Froude number upstream of weir, at the inlet, which was kept at about 10m from the weir. However the flow depth reduces significantly by the time it reaches the weir.
How do I accurately model to obtain the required values of flow depth and Froude number upstream near the side weir?