Case Study: Improving real-time stage forecasting Muskingum model by incorporating the Rating Curve Model

Analysis of forecasts obtained by a forecasting model of the Muskingum type for real-time application, called STAFOM, shows that the model provides accurate forecast stage estimates for most of the selected case studies and flood events in the Upper-Middle Tiber River basin in Central Italy. However, three main issues affected STAFOM and in particular a) its kinematic nature, b) the lateral inflows representation and, finally, c) the occurrence of sudden fluctuations in water levels observed at the ends of the equipped river reach. Therefore, this simple stage forecasting model is here improved by incorporating a methodology relating local stage and remote discharge along river channels. This latter procedure, based on the Rating Curve Model (RCM), is capable of reconstructing discharge hydrograph at a river site where only stage is monitored, while the discharge is recorded at another section located far away and for which a significant lateral inflow contribution is expected. Application of the new model, named STAFOM-RCM, to several flood events that occurred along four equipped river reaches of the Upper Tiber River basin, shows that it improves the stage forecast accuracy both in terms of peak and stage hydrograph mainly for long river reaches, thus allowing to consider a longer forecast lead-time and hence avoiding the use of the old two-connecting river branch scheme which amplified the fluctuations in observed water levels.