Современные изменения водного режима и морфометрии рек Верхнедонского бассейна

Abstract

The article substantiates the methodology of distinction between the Upper and the Middle basins of the Don river. The suggested demarcation line, undefined until now, should coincide with the administrative border of the Voronezh oblast in the south, south-east, east and north-east. This approach allows us to analyze the water regimen of the Don river proper and it’s tributary, Khoper river, as an integrated Upper Don river basin. The annual river flow of the rivers Don and Khoper is diminishing, but the trend is weak and statistically insignificant. The duration of the spring snow floods is increasing due to its earlier onset and later ending. The peak water volumes have been steadily declining because of a change in the maximum water flow genesis under conditions of a steady increase of air temperature and decrease in frost penetration in the soil. The maximum flood levels are observed to occur more often in March, that was not registered before early 70's, with the increase of floods repetition in May, whereas the April prevalence is diminishing. The absolute spring-fall low water minimums are shifting mostly towards September, while the winter ones tend to happen in February and March, right before the spring flood season. This leads to decreases in seasonal unevenness of the river runoff volume and increases the length of a relative “average water” periods throughout the year. The resulting negative dynamics in the river morphometry is due to the pre-spring thaws and floods, changes in the spring floods’ genesis and character, lesser depth of the frost penetration, less contact between the soil and the flood waters, as well as destruction of the creek network and the slope runoff. We have registered the accelerated decrease in small watercourses, as well as the increase in the number of waterless valleys, dry waterbeds, and sporadic watercourses. The rivers Sosna and Kamenka, right-bank tributaries of the Don river, have demonstrated the 8.2 and 45% respective decrease in the riverbeds’ length, the most prominent in the current century.