HYDROLOGICAL CHARACTERISTICS OF FLOODS IN THE ERTIS RIVER BASIN

Abstract

This study presents a comprehensive analysis of extreme flow parameters and hydrological flood hazard characteristics in the Irtysh Water Management Basin based on long-term hydrological observations. The main river, the Irtysh, is one of the primary waterways of Kazakhstan. It is a transboundary river heavily utilized by two neighboring nations—the People's Republic of China and the Russian Federation. The objective of this work is to provide a comprehensive assessment of the statistical characteristics of maximum water discharges (Qmax) and peak water levels (Hmax), test the homogeneity of hydrological series, and determine the calculated values of discharges and levels for various exceedance probabilities (1 %, 3 %, 5 %). Furthermore, these values are compared with floodplain alignment elevations and historical floods in the region to substantiate inundation boundaries for subsequent hydrodynamic modeling aimed at assessing flood risk. In the first stage, initial data processing was performed, including the restoration of missing observational data and the evaluation of series homogeneity for maximum water discharges. Fisher, Student, and Wilcoxon tests, along with Mann–Kendall, Pettitt, and Buishand tests, were applied to verify statistical homogeneity. This enabled the assessment of stability, absence of systemic shifts, and comparability of hydrological observations across various streamflow gaging stations in the basin. Based on the verified series, a statistical analysis of maximum water discharges was conducted to determine the primary distribution parameters, including the coefficient of variation (Cv) and the coefficient of asymmetry (Cs). For catchments exhibiting high variability, truncated Kritsky–Menkel distribution functions were applied. The resulting statistical characteristics were used to calculate maximum water discharges and levels for specified exceedance probabilities (1 %, 3 %, 5 %), reflecting the likelihood of extreme hydrological events. A comparative analysis of long-term maximum discharge dynamics across various gaging stations revealed the spatial patterns governing extreme runoff formation. Additionally, comprehensive processing of long-term data was carried out, incorporating the restoration of missing peak water level values and the analysis of their multi-year dynamics. By comparing recorded water levels with floodplain inundation thresholds, specific years of floodplain flooding were identified, and parameters for maximum water levels of various exceedance probabilities (1 %, 3 %, and 5 %) were calculated.