THE FEATURES OF THE OKA RIVER LONGITUDINAL PROFILE DEVELOPMENT UNDER THE ANTHROPOGENIC DISTURBANCES OF THE RIVER BED

Abstract

Based on the analysis of cartographic documents and hydrological data, as well as detailed studies of fl uvial processes in the Upper Oka, carried out in 1990-ies and continued in 2010–2015, it was found that the longitudinal profile of the river was significantly infl uenced by anthropogenic river bed disturbances – exploitation of in-stream mines of alluvial construction materials, concentrated in the middle reaches of the river within 400–800 km from the source. Changes in river bed morphology and sediment deficiency has resulted in the deep erosion. To determine the role of anthropogenic disturbance in the longitudinal profile formation, in accordance with the N.I. Makkaveyev’s approach, the calculation of graded longitudinal profile and its comparison with real one were performed. By calculating the stream-gradient index proposed by J. Hack, the uneven gradient distribution was revealed along the entire river and on separate typical sections. The highest values of the stream-gradient index observed at the site where mechanical modifications are the most – between Kaluga and Kolomna Cities. On this stretch of the river in the late 1930s, the longitudinal profile in most aspects practically coincides with the calculated graded profile. However, mechanical changes of the river bed and the accompanying river bed degradation has led to the fact that along with general elevation decrease, profile became ungraded, and one can expect some deformations aimed at its restoration. As a result, the difficulties in using the resources of the river, which emerged in the early 1990-ies, have increased.