Results of the numerical modelling of intra-annual variability of hydrological characteristics of the Kuialnytskyi Lyman lagoon under various runoff volumes of the Velykyi Kuialnyk River

Assessments of changes in the intra-annual spatio-temporal variability of the hydrological characteristics of the Kuialnytskyi Lyman lagoon under various runoff volumes of the Velykyi Kuialnyk River were obtained from the results of calculations, using the predictive three dimensional hydrothermodynamic model Delft3D-FLOW. Scenarios of increasing the river runoff inflow up to 25% and 75% of the monthly natural river runoff under conditions of 2015 were modelled, as well as under different by hydraulicity typical years of the modern climatic period of the 21st century (1990-2030), determined according to the most appropriate for the Kuialnytskyi Lyman lagoon region climatic scenario from the ENSEMBLES database, which corresponds to the global A1B scenario, calculated by the MPI-REMO model. Monthly values of the natural runoff of the Velykyi Kuialnyk River, calculated with the use of “climate-runoff” model, were used during the simulation. Implementation of water management within the catchment area of the Velykyi Kuialnyk River and realization of various engineering and technical measures aimed at the increase of river inflow to the Kuialnytskyi Lyman lagoon, are identified to significantly affect the hydroecological regime of the lagoon only in case of supplying at least 75% of the natural river runoff volume into the lagoon. The increase of the natural runoff of the Velykyi Kuialnyk River is incapable to provide the stabilization of the hydroecological regime of the Kuialnytskyi Lyman lagoon independently, without periodical replenishment of the lagoon with seawater from the Odessa Gulf. Under the absence of replenishment of the lagoon with sea water and deficiency in the runoff of other small water streams flowing into the lagoon, the increase of the runoff of the Velykyi Kuialnyk River even up to 75% of the volume of its natural runoff could provide the stabilization of the annual cycle of water level and salinity variability in the lagoon only during the high-water years.