Description of artificial reservoirs within the catchment area of the Great Kuyalnik River and regulation of their operation at the present time and in future

Abstract

The paper presents the results of surveys of artificial reservoirs of the Great Kuyalnik River and its tributaries which, due to their considerable number and filling volumes, significantly reduce the runoff of the river and thus cause shallowing of the Kuyalnik Liman and deterioration of its hydroecological state. Preparation of a list of artificial reservoirs within the catchment area of the Great Kuyalnik River took place using the data of the Odessa Regional Water Resources Administration and satellite images taken from Google Earth and Google Maps applications. Water surface areas and volume of unexplored water bodies were determined via generalization of existing data for other reservoirs using the invariance postulates considering the morphology of the arid zone. It was established that, as of 2016, the total number of artificial reservoirs is 121 with a total filling volume constituting 15.98 million m3. Using the climate-runoff model the characteristics of the natural runoff (not disturbed by economic activity) were estimated for periods before warming and for 2021-2050 (scenario A1B). To assess a degree of influence of artificial reservoirs on the state of the ecosystem the accumulation coefficient is calculated. It is shown that the coefficient of water accumulation in artificial reservoirs increased from 0.76 in past century to 1.23 after warming (scenario A1B). This circumstance indicates a tendency towards lack of free (unregulated) runoff in the river and formation of its deficit. The loss of runoff because of filling of artificial reservoirs exceeds the runoff of certain tributaries and ultimately the river's runoff itself. This leads to reduction and complete cessation of fresh water entering into the Kuyalnik Liman which gradually dries up. In order to regulate the impact of artificial reservoirs on the river's runoff it is necessary to determine permissible (limiting) volumes of their filling. These volumes were defined as 10 and 25 percent of the natural annual runoff. The natural (not disturbed by economic activity) annual runoff of the river was calculated on the basis of the climate-runoff model using meteorological data. Under conditions of warming the natural runoff of the river and the associated permissible (limiting) volumes would decrease which would require reduction of an even greater number of ponds.