1D unsteady-state flow simulation of a section of the upper Rhine

A 1D steady-state flow simulation model was developed. A module evaluating the roughness parameters due to the surface roughness of the main channel and floodplains, riparian forests on the floodplains, and the momentum exchange between the main channel and floodplains was introduced into the model. In the module, the roughness parameters were evaluated by the formulas proposed by the DVWK [Hydraulische Methoden zur Erfassung von Rauheiten (1990); Hydraulische Berechnung von Fließgewässern (1991)] for steady and uniform flow conditions. The model was calibrated with data obtained from three flood events. Roughness parameters of the main channel and floodplains of both sides were identified in the situation before May 1999. The morphological situation changed slightly. Several sensitivity analyses were carried out for the following cases: (a) the morphological situation before May 1999 with the original parameters, (b) the situation of (a) with various parameters to the realistic extent, (c) the situation being so that the floodplain on the German side were imaginarily enlarged up to utmost 90 m with the original vegetation, and (d) the situation of (c) with various parameters to the realistic extent. Many combinations of the roughness parameters due to the bed roughness and density of the vegetation were examined. The results showed that the most significant parameter is the bed roughness of the floodplains, and the next is that of the main channel. A modification of parameters of the riparian vegetation is of minor importance. The model was extended to a 1D unsteady state flow simulation model and applied to two flood data obtained in the reach between Rheinweiler (186.156 km from Lake Constance) and Hartheim (214.244 km) in Germany in 1998 and 1999. Both measured and calculated hydrographs at Hartheim had their peak discharge at the same time, and the discrepancy of the discharge between the measured and calculated hydrographs was less than 10%.