Methodological basics of forecasting floods on the rivers of Transcarpattia

Abstract

The formation of floods of mixed origin in the cold and warm periods of the year is characteristic of the rivers of Transcarpathia. They are often accompanied by significant and prolonged flooding of territories, sometimes with catastrophic consequences. For the purpose of warning about dangerous hydrological phenomena, an urgent task is hydrological forecasting of maximum levels and water flows during periods of floods on rivers. The object of the research is the Tysa River and its tributaries, which are characterized by the formation of maximum runoff from melting snow and rainfall in the winter-spring period. The Carpathians, which occupy the southwestern part of Ukraine, play a major role in shaping the climate of the territory under consideration, where a mountain climate associated with heavy precipitation is created. It should be noted that heavy precipitation in the Tysa river basin is characterized by a long duration and intensity of precipitation. Such rains are accompanied by the rapid formation of catastrophic river floods, mudslides and floods. The purpose of this work is the analysis of modern mathematical models for forecasting the maximum water levels and discharges of floods and the creation of a methodology for short-term forecasting of the flood flow of Transcarpathian rivers. Mathematical models of rain and snow-rain runoff of mountain rivers were developed as structural components of basin prognostic systems (in the Tysa basin - "Tysa", in the Latorica river basin - "LATORICA", 2011). Such models were created at the Ukrainian Research Hydrometeorological Institute of the State Emergency Service of Ukraine and the National Academy of Sciences of Ukraine (UkrHMI) https://uhmi.org.ua/dep/hydro/ and are implemented in the operational activities of the Transcarpathian Regional Center for Hydrometeorology http://gmc.uzhgorod.ua/vgpro.php. These models are conceptual with concentrated parameters and serve for short-term forecasting of runoff (discharges /levels) during rain and snow-rain floods and long-term forecasting of spring flood characteristics. In foreign practice, a new generation MIKE 11 modeling complex has been developed and is used in the operational practice of European countries. In UkrHMI, the adaptation of the NAM RR MIKE 11 hydrological model to calculation and forecast modeling of both average daily and maximum discharges of the mountain rivers of Transcarpathia (the rivers Tysa, Rika, Borzhava). The quality of NAM module calibration is related to the quality and availability of hydrometeorological data and the impact of anthropogenic activities on river flow. In addition, as part of the adaptation of the MIKE 11 model, predictive hydrological modeling was carried out based on the data of the WRF NMM mesoscale short-term weather forecast model and satisfactory results were obtained. The basis of the development of the method of forecasting the maximum flood water levels by the authors is the method of appropriate levels for the Tysa River, taking into account the data of automatic posts under different conditions of the formation and superimposition of flood waves along the river and its tributaries. The physical basis of the method of forecasting discharges and water levels in river sections is the Saint-Venant equation, which reflects the basic patterns of movement of river waves in a one-dimensional approximation. The essence of the method is to establish an empirical relationship between the appropriate levels (discharges) of water observed in the upper and lower reaches. The prematurity of the forecast is equal to the difference in the timing of the occurrence of such levels (discharges) in the specified creations. Thus, in order to warn about the negative consequences of passing the maximum water levels of floods of mountain rivers of Transcarpathia, which are caused by heavy precipitation or melting snow, it is carried out both when using modern prognostic mathematical models and when using the method of appropriate discharges or water levels.