Relating local stage and remote discharge with significant lateral inflow

The development of a simple model for reconstructing the discharge hydrograph at a river site where only the stage is monitored and the discharge is recorded at another upstream section, is outlined. The model is designed to also accommodate significant lateral inflow contributions, permitting, without using a flood routing procedure and without the need of a rating curve at a local site, to relate the local hydraulic conditions with those at a remote gauged section. The approach is tested through its application to different flood events observed in three equipped river reaches of the Upper Tiber basin (Central Italy) where the contributing drainage area is significant. The simulated discharge hydrographs were found in a good agreement with those observed at the downstream ends of the investigated reaches. Errors in peak discharge and time to peak show that the model is suitable for estimating the rating curve beyond the range of the available streamflow measurements once an accurate stage-area relationship is assessed. Finally, the proposed approach was found more reliable than that based on the Muskingum method incorporating the water level observed at the downstream end.