As a result of scientific researches, the scientific and applied task of improving the complex water use in the zone of influence of the Dnipro-Donbas canal has been solved with the provision, on the basis of modeling, quality of water resources for drinking needs, reservoirs ecological sanitation and ecological compensatory releases in the Siversky Donets River, for the development of irrigated agriculture.
Based on the results of the ecosystem-based spatial-temporal analysis of water quality for drinking needs in the Dnipro-Donbas canal for the period of 2010-2016, excess maximum permissible concentrations of such substances as general rigidity and mineralization, sulfate content, indicators of permanganate oxidation, turbidity and staining are established. The water of the canal belongs to the second class of quality, it is "good, clean, acceptable quality" on the area from Shulgovka to the Krasnopavlivske reservoir. According to the results of calculations of ecological water quality assessment, the systematic high level of water pollution in the canall system is determined by the content of sulfates and the indicator of transparency (6th and 7th categories of 4-5 classes).
The assessment of water quality in the Dnipro-Donbas canal showed that according to agronomic and environmental criteria, irrigation water is classified as I Class and is suitable for irrigation without constraints on the section of the canal from the monitoring point in the Shulgivka village to the Krasnopavlivske reservoir.
According to the results of ecosystem studies of spatial and temporal patterns of surface water quality formation in the Dnipro-Donbas canal system, the need for water exchange for drinking and communal water use and ecological releases for the improvement of the Siversky Donets River is established.
The mathematical modeling of water exchange provides an opportunity to monitor the daily changes in hydrological and hydrochemical parameters, the processes of transporting and mixing water masses of various quality in the Orilsky and Krasnopavlivske reservoirs, the time of the onset of the water quality planned result and the water exchange duration.
Based on the scenario analysis method, the estimation and comparison of water supply options in the Krasnopavlivsky Reservoir on the ecological (rigidity index) and the economic (volume of water consumption for water exchange) criteria were evaluated and compared.
A scenario analysis has shown that water exchange options are controversial in terms of environmental and economic criteria: the environmental criteria decreases, while economic growth increases. There is a need for two-criterion optimization in the Pareto region, which is carried out to achieve compromise solutions based on economic and environmental criteria.
The developed method and models for assessing the change in water demand, when comparing two and more time periods, make it possible to adjust irrigation rates in conditions of climate change with paid water use.
Key words: integrated water use, mathematical model, drinking water supply, ecological assessment, water quality, water exchange, water consumption norm.
