Optimal policy of irrigation and drainage wells systems in affected agricultural lands

Abstract

During the last decades, important areas of the Romanian agricultural lands are confronted with some specific problems. In South, due to an inefficient system of irrigation, appears the salting effect. In drought years, entire surfaces are covered with white phosphates (used in excess thirty-forty years ago), destroying the agricultural plant’s roots. Contrary, in East, due to improper management of riverbeds, after floods, appear surfaces confronted with excess quantities of water deposition (sometimes even for one entire month), destroying also the agricultural plant’s roots. In the present paper, a solution for estimation the necessary level of the water table is presented, assuming a correct correlation between the irrigation during the vegetation period and the drainage during the rest of the year. An agricultural land irrigated by gravity, from the Jiu River basin, is considered, long enough and extended between two emissaries with low topographic incidence. The computational scheme, for unsteady flow with the initial level of groundwater, corresponding to a stationary regime of drainage or injection is adopted. The boundary conditions consist of imposed groundwater levels at areas extremities, in accordance with the known levels of the emissaries. The objective function is defined as a sum of cumulated rates for standard deviations, between the groundwater flow and the water table level, during two years. Some major coefficient’s penalties for the waiting time intervals are assumed, to limit the excessive water during the vegetation. A detailed analysis of the underground flow, the numerical model, the obtained results, conclusions, and references are also mentioned.