AN ENVIRONMENT ASSESSMENT, MODELLING AND FORECAST OF THE SALTED REGIMES OF IRRIGATED ARABLE LANDS IN ARID REGIONS

Abstract

The forecast of the salt regime of irrigated lands is an obligatory part of the complex of surveys and research for the goals of meliorative building, reconstruction of irrigation systems in the course of their operation. Assessment of the salinization risk of pod soils in the south of Ukraine is a special topic. The theory of physical and chemical hydrodynamics of porous media is the basis for modern methods of predicting salts transfer. Mass transfer processes are described by differential equations of motion and conservation of matter mass of the second order in partial derivatives of elliptic and parabolic types according to this theory. One-dimensional versions of these equations are used for solving practical problems. This is due to the fact that salt transfer in the aeration zone takes place mainly in the vertical direction. The purpose of the research was to substantiate the possible optimal models of the vertical salt transfer at the example of irrigated land. The object of research is represented by the subgrade of the earth's surface in the Solonyansky district of the Dnipropetrovsk province. The scheme of salts transfer was drawn up according to the steps taken. The origin of the coordinates was linked to the earth's surface. The boundary condition of the III-kind of Danckwerts−Brenner was specified for it. Its physical meaning: the amount of salt that enters the earth's surface during irrigation is dispersed in the aeration zone according to the laws of molecular and convective diffusion. The migration parameters were determined by solving an inverse problem. The rate of vertical moisture transfer was determined by the balance method. Salinity was determined at three vertical points using Verigin's analytical solution to determine the hydrodispersion parameter. The forecast of the soil salt regime in the annual decrease in the territory of the proposed irrigation with a salinity of 0.9% was made taking into account the initial data. The calculations made it possible to determine the values of the parameters of salts transfer. According to the calculations, the salinity of the soil on the surface of the study area will be 0.322%. The calculation process was performed again after increasing the irrigation rate. The results of the calculation show that under a given irrigation regime, the upper meter layer will not be desalinated (when salt content less than 0.25%) for 5 years without increasing the irrigation rate to 3000 m3 /ha.