干旱区平原水库坝后排水沟对下游农田土壤水盐运移的影响

干旱区平原水库的渗漏会抬高坝后农田地下水位,使土壤发生盐渍化,许多土地因此减产甚至弃耕。坝后设置排水沟是一种有效控制农田地下水位的措施。本研究采用排水沟调控坝后农田的地下水位,并利用HYDRUS模拟出在不同地下水位和深度的条件下土壤含水率与含盐量的变化情况,将实测数据与模拟数据相互对比,检验出模拟值的可靠度。研究结果表明:地下水位通过排水沟从1 m降到3 m,表层含盐量相差1.49～33.19 g·L~(-1),因此排水沟遏制地下水位越深,水盐运移越不明显,次生盐渍化越不容易发生,反之,则容易发生土壤盐渍化;地下水位相同时,土体种植植物可以降低含水率和含盐量,其中含水率最大变化为6.33%,含盐量仅相差0.08～4.56 g·L~(-1)左右,而且随着土层深度增加其影响的程度也逐渐减小。设置排水沟是解决坝后农田土壤盐渍化的较好方式。

Effects of drainage ditches behind dams of plain reservoirs on soil water and salt transport in downstream farmland in arid regions

The seepage of plain reservoir raises the groundwater level of farmland behind the dam in arid area, which results the soil salinized. Consequently, production is reduced or even abandoned. It is an effective measure to control the farmland groundwater level to set drainage ditch behind the dam. The change of soil water and salt transport after changing groundwater depth is worth of studying. Therefore, drainage ditches was used to regulate the groundwater levels behind the dam in this study, and HYDRUS was used to simulate the soil water content and salinity at different soil depths and different groundwater levels. The reliability of the simulated values was verified by the measured data. The results showed that the groundwater level decreased from 1 to 3 m through drainage ditches and the difference of surface salinity was between 1.49~33.19 g·L^-1. Therefore, the deeper the groundwater level in the drainage ditches, the less obvious the water\|salt migration,the less likely secondary salinization would occur. Otherwise, soil salinization would occur easily. When the groundwater level was the same, planting could be used to reduce water content and salt content, the maximum change of water content was 6.33%, the difference of salt content was only about 0.08~4.56 g·L^-1 and the influence gradually decreased with the increase in soil depth. Therefore, setting drainage ditch is a best way to solve soil salinization behind dams to drain the seepage water from reservoirs in time.