When calibrate the model I have matched the simulated water surface elevation with observed water surface elevation by changing Manning’s coefficient of floodplain. The results are almost match from starting water level to reach peak level (rising limb of hydrograph) but when the water level reduces the simulated water level did not reduce as much as observed level reduces (falling limb of hydrograph). I shall be grateful if you could explain me what changes i have to do in the model to get close matching between observed and simulated during falling limb of hydrograph. Thanks in advance.