ASSESSMENT OF CAUSAL MECHANISMS ON FLOOD CONVEYANCE ALONG THE TISZA RIVER, HUNGARY USING ONE DIMENSIONAL RETRO AND SCENARIO MODELING

Previous research on the Tisza River in Hungary showed increases in flood stages for fixed discharges (above bankfull). These results showed that a loss of conveyance has taken place on the Tisza River, contributing to recent record flood levels. In order to assess the potential causes of flood conveyance losses, new hydrological and geospatial data were obtained from the Hungarian Federal Hydrological Authority (VITUKI) in order to develop hydrodynamic models for two reference conditions, 1978 and 1999, along a 230 km study reach of the Middle Tisza River. In addition to these models of actual conditions at each time step (i.e., “retro-models”), three “scenario models” were developed in order to test the individual impacts of each of the hypothesized causal mechanisms: 1) channel geometry 2) land cover (roughness), and 3) levees. Comparison of the models for actual conditions and the scenario models allows for quantitative assessments of the impacts of each of these parameters on flood conveyance. Preliminary results suggest that increases in flood stages between 1978 and 1999, which vary from negligible to 1.0 m at some locations, result from a combination of changes in channel cross-sectional area and roughness-driven flow-velocity changes.