Impact of ponds and reservoirs construction on the environmental safety of small river basins of the steppe zone of Ukraine (the case of Dnipropetrovsk region)

Formulation of the problem. For the last 30 years, water management in the basins of small rivers in the steppe zone of Ukraine has led to a deterioration of the environmental safety in water use. The current ecological state of small rivers is close to critical, and for today some river basins are subject to catastrophic environmental changes. Almost all small rivers from 70 to 100% in the south and central water-short regions of Ukraine are under regulation due to the construction of a large number of ponds and reservoirs. In most cases, this causes a lack of transportation and low self-cleaning ability. Thus, the conservation, restoration and rational use of water, based on the principles of basin management, should get started along with the improvement of the ecosystems of small rivers. Research results. The paper describes the dynamics of changes in water management, which shows a rapid increase in the number of new ponds in the period of 1990 - 2018 almost threefold. At the same time, the overall dynamics of water consumption in the region in the same period decreased fourfold. Unjustified imbalance between the construction of new facilities and water demand was determined, as well as non-compliance with the current statutory provisions. Due to the transformation of natural watercourses into cascades of "evaporator ponds" an ecologically dangerous transformation of small river basins with the change of hydrological, hydrochemical, hydrobiological and sanitary regimes takes place. To evaluate the level of environmental hazards associated with water management, it is proposed to determine the river fragmentation coefficient, which is the ratio of the number of ponds and reservoirs to the length of the river. When evaluating the environmental hazard for rivers in a specific territory (administrative area, district or catchment area), the fragmentation coefficient is determined by the ratio of the number of ponds and reservoirs to the size of the territory. Comparative analysis indicates that Dnipropetrovsk region is one of the most environmentally dangerous in terms of the negative impact of river basins fragmentation by artificial reservoirs. The case of a small river basin (the Nyzhnia Tersa River) presents the application of the approach to evaluate the level of environmental safety associated with water management. It is proposed a mechanism for increasing the level of environmental safety in water use by observing and implementing heterogeneous groups of indicators that determine the overall efficiency of the river ecosystem functioning. Conclusions. In order to stabilize and restore the hydrological and ecological state of small rivers in the steppe zone of Ukraine, it is important to: 1) make a detailed evaluation of the compliance of the available number of ponds and small reservoirs in river basins with the requirements of the Water Code of Ukraine; 2) prove ecologically and economically the feasibility of further operation for each individual reservoir and structure; 3) develop regional programs for the elimination of ponds and reservoirs that do not fulfil their water management functions and cause environmental hazards to the functioning of the river basin ecosystem; 4) improve methodological approaches to evaluation of the environmental safety of water facilities in small river basins.