Morphodynamic assessment of the Sava River’s critical navigational section

Waterways can become underutilized transport potential because of riverbed degradation and reduction of low flows driven by the climate change. Long-term changes of river’s morphology are driven by sediment supply that is intensified during flood events and influenced by the flow dynamics and associated sediment transport. Morphodynamic changes directly impact riverine ecosystems, infrastructure, and flood risk management, and extended periods of low flows can pose critical obstacle for navigation, present considerable pressure on navigation management and reduce the transport efficiency. This study presents morphodynamic assessment of the Sava river’s section in Croatia identified as critical from the navigational perspective. Flow regime of the critical river reach is analysed using 1D HEC-RAS model. The aim of the paper is to evaluate the current condition of the river waterway, determine critical zones that can impede the navigation and define relevant parameters for long-term monitoring with purpose of fairway management. The 1D model is calibrated using the water levels and flow rates from the gauging stations and validated against the field ADCP data. Results show the satisfactory efficiency of the 1D model for interpretation of riverbed degradation and aggradation, while keeping the banks stabilized to reflect the constructed river training structures, mostly revetments, on both banks. The apparent one dimensionality of the flow enforced by the river training structures enable reliable use of the sediment transport equations over the period of few years, but the model is highly sensitive to the selection of the sediment transport equation.