Pressurized groundwater recharge in the zone of influence of the collector-drainage network of the southern Mirzachul Oasis

Abstract

The paper examines the hydrogeological conditions of the formation and manifestation of pressurized groundwater recharge within the drainage influence zone on irrigated lands in the southern part of the Mirzachul Oasis. Based on field observations of the piezometric levels of confined groundwater at depths of 5, 10 and 20 m, the groundwater regime and the character of the seepage flow in a stratified soil-ground system complicated by low-permeability layers are analysed. Over the annual cycle the groundwater level varied between 3.05 and 3.85 m, with an average of 3.46 m, while the pressurized groundwater level varied between 2.25 and 3.02 m, with an average of 2.52 m; the resulting head difference ranged from 0.50 to 1.25 m, averaging 0.94 m. The hydraulic conductivity averaged 0.24 m/day at 3–5 m, fell to 0.04–0.07 m/day at 14–18 m and rose to 1.0–3.0 m/day in the main aquifer at 20–40 m. The calculated hydraulic gradient was 0.030 in the vegetation period and 0.040 in the non-vegetation period, with recharge values of 3022 and 4004 m 3 /ha. The impact of pressurized groundwater on the water-salt regime of the upper aeration zone and on the efficiency of the collector-drainage network is demonstrated.