ONE-DIMENSIONAL RETRO AND SCENARIO MODELING FOR TWO TIME STEPS ACROSS THE MIDDLE TISZA RIVER, HUNGARY

Previous research on the Tisza River in Hungary found that four of the six gauging stations analyzed showed significant increases in stage for fixed flood discharges (flows above bankfull), indicating a loss of conveyance and contributing to recent record flood levels on the Tisza. In order to assess the potential cause of the change in flood conveyance along the Middle Tisza River, new hydrological and geospatial data were obtained from the Hungarian Federal Hydrological Authority (VITUKI) in order to develop hydrodynamic models for two reference conditions, 1934 and 1970 (i.e., “retro-models”), along a 100 km study reach. For each reference condition, four 1-D hydrodynamic models were developed. These models include a calibrated model of actual conditions at each step and three “scenario” models: 1) a model with levees of the next time step, 2) a model with the channel geometry of the next time step, and 3) a model with roughness (i.e., land cover) of the next time step. Comparison of the model for actual conditions and the scenario models allows for a quantitative assessment of the impacts of each of these parameters on flood conveyance. Preliminary results suggest that increases in flood stages between 1934 and 1970, which vary from negligible to nearly 2 m at some locations, result from a combination of changes in channel cross-sectional area and/or roughness-driven flow velocity changes. These observed increases in Tisza flood and flow dynamics are currently being independently assessed by scenario modeling in order to determine the causes of decreased flood conveyance along the Middle Tisza River.