间歇性生态输水塔里木河下游断面地下水位变化模拟

地下水作为干旱区生态系统的重要组成部分,对植物生长具有重要作用。以塔里木河下游英苏断面2011—2015年逐月地下水埋深变化为研究内容,基于非稳定流理论,以河道附近水位边界条件作为初始求解条件,以余误差函数erfc(x)为求解函数,综合考虑地下水变化时间滞后效应及潜水蒸发作用,旨在构建间歇性输水河道地下水埋深变化模型。结果表明:(1)生态输水期间,在短期内,临近河道地下水埋深波动较大,而远离河道地下水埋深波动并未受到较大的影响,生态输水作用影响河岸附近地下水埋深变化存在一定时段的滞后期,且随着距离河道的增加,滞后期增长。(2)以河道为基点的地下水非稳定流运动及潜水蒸发作用是影响沿岸地下水变化的诸多环境因子中最敏感的因子。(3)模拟结果表明基于非稳定流理论对塔里木河下游地下水变化模拟效果较好,达到了地下水模拟精度的要求,对塔里木河下游断面尺度上地下水恢复状况研究及后期生态恢复评价具有重要的理论意义与参考价值。

Simulation of sectional groundwater level variation in the lower reaches of Tarim River under intermittent ecological water conveyance

As an important component of arid ecosystems, groundwater plays an important role in plant growth. We used the unsteady flow theory as the method, residual error function erfc(x) as the solution function, and time lag effect of groundwater depth change and phreatic evaporation as the basic condition to construct a monthly average groundwater depth change model from 2011 to 2015 of the lower reaches of the Tarim River Yingsu-section based on intermittent water conveyance. The results indicated that:First, during the period of ecological water conveyance, groundwater depth near the river channel fluctuates greatly in a short time, whereas fluctuation in groundwater depth was not greatly affected far from the river. This shows the influence of ecological water transport on groundwater depth near the river bank, which has a certain lag period, and the lag time increases gradually as distance from the river increases. Among all monitoring wells, the C4 monitoring well showed the shortest lag period, whereas the C7 monitoring well showed the longest lag period. Second, the unsteady flow of groundwater and phreatic evaporation were the most sensitive factors influencing the change in groundwater depth. The action of unsteady flow showed the greatest influence on groundwater depth during monthly variation and annual variation. The effect of phreatic water evaporation on the change in groundwater depth was small in the short term; however, the total influence of groundwater depth over many years cannot be ignored. Third, in core monitoring of the lower reaches of Tarim River, Populus-Tamarix chinensis-meadow mixed zone, meadow, meadow-desert mixed zone, and semi-desert were observed within 1050 m of the Yingsu-section, which require different groundwater depth. The simulation of groundwater depth changes in the lower reaches of Tarim River are based on the unsteady flow theory, with fitting accuracies (R²) at 300, 500, 750, and 1050 m of 0.701, 0.654, 0.701, and 0.625, respectively. These values meet the requirements for groundwater simulation accuracy and have important theoretical significance and reference values for studying relationships between groundwater and vegetation restoration in the lower reaches of Tarim River. This research will provide a reference for the simulation of groundwater level in arid area, which can be used to simulate the change of groundwater level at any location within the influence range of the river. Further exploration will improve the efficiency of ecological evaluation at a certain extent.