Water regime specifics in the upper Sviyaga River and its tributaries upon karst development

At present, the hydrological characteristics of small rivers are understudied in Russia. Taking into account the increasing deterioration of the ecological state of surface watercourses, which primarily affects the intra-annual distribution of water runoff on small and medium-sized rivers, in particular, the study of runoff formation, its variability and intra-annual changes become the most important task of hydrology. The paper considers changes in the indicators of intra-annual distribution of river flow in the upper reaches of the Sviyaga River in the almost complete absence of knowledge of changes in the flow of small and medium-sized rivers in the study area. It was necessary to identify what changes the water runoff from small and medium-sized rivers undergoes in the upper reaches of the Sviyaga River, which is complicated by the occurrence of karst. The paper presents an analysis of the intra-annual distribution of water runoff, and natural factors that have the maximum effect on the intra-annual distribution of water runoff for rivers in the study area, as well as its assessment against the background of climate change. The identified types of water regime are described. Based on the research results, a typification of rivers is proposed according to the annual water flow and zoning of cross-sections by river types. The intra-annual distribution of water levels and discharges are analyzed, the factors influencing them are assessed, and the most significant of them are identified.