Reclamation of Irrigated Lands and Improvement of the Groundwater Regime Under Vertical Drainage Operation

The aim of the study was to identify patterns of seasonal groundwater-level fluctuations and assess the effectiveness of vertical drainage in regulating the reclamation regime of saline lands in Kazakhstan. The methods included monitoring-well observations, calculation of seasonal amplitudes, Student’s t-test, the Mann-Whitney U test, and Pearson correlation analysis. Before the growing season, groundwater occurred at a depth of 1.5-1.7 m, corresponding to the critical threshold for secondary salinisation. By days 5-6 after the inflow of irrigation and meltwater, groundwater became shallower rapidly, with the rate of shallowing increasing from 0.20-0.30 m/day during the initial stage to 0.80-0.90 m/day. From 2021 to 2024, a stable annual cycle was recorded: a spring shallowing to 1.4-1.6 m depth, a summer deepening to 2.5-3.3 m depth. Drainage-system operation remained stable throughout the leaching period. The average discharge was 38 L/s, while the volume of pumped water ranged from 260.35 to 325.45 thousand m³. The efficiency coefficient remained at 0.96-0.97 despite a reduction in operating duration from 10 to 8 days and a decline in energy consumption toward the end of the cycle. Seasonal analysis showed that operational coefficients of 0.25-0.30 maintained stable drainage during transitional and summer periods, whereas a coefficient of 0.50 was required during periods of increased hydrological load. The findings confirm that vertical drainage effectively regulates groundwater levels, supports a stable reclamation regime, and reduces the risk of secondary soil salinisation. The results can be used to set vertical-drainage operating coefficients at 0.25–0.30 during stable summer conditions and increase them to 0.50 during spring and early-autumn peak recharge to maintain groundwater below the secondary-salinisation threshold while reducing unnecessary pumping and energy consumption.