季节性冻融区井渠结合灌域地下水动态预报

该文以河套灌区永济灌域为研究对象,建立考虑冻融影响的分段式水均衡模型,预报12种井渠结合节水情景的地下水动态响应。结果表明:冻融期间气温对地下水埋深的影响在时间上滞后46.5 d,两者相关关系明显;地下水开发利用越多、秋浇采用黄河水的比例越小,节水规模越大,同时地下水位下降越明显。12种节水情景中,节水规模占现状引水量的5.7%~15.5%,全灌域平均地下水埋深增加0.05~0.24 m,井渠结合区地下水埋深增加0.16~0.38 m;灌域引黄水量与地下水埋深关系用二次函数进行拟合,决定系数R~2达到0.88以上;灌溉水利用效率的提高以及地下水位下降引起潜水蒸发的减小是井渠结合节水的实质。分析结果表明,考虑冻融影响的水均衡模型简单实用,可为中国西北干旱半干旱地区开展井渠结合地下水响应预报提供参考。

Groundwater dynamics forecast under conjunctive use of groundwater and surface water in seasonal freezing and thawing area

Water resources allocation for agriculture irrigation in the Yellow River basin will be reduced due to water shortage and increasing demand for non-agricultural use. Different measurements should be taken to save water and to ensure the sustainable development of agriculture. The conjunctive use of groundwater and surface water is one of the most promising water-saving measurements by decreasing evaporation and increasing water efficiency. However, it also could result in adverse effects on the local environment such as soil desertification when over-extraction of groundwater occurs. Therefore, it is necessary to estimate the water dynamics accurately when implementing the conjunctive use of groundwater and surface water irrigation in the target district. In this paper, Yongji irrigation sub-area of Hetao irrigation district as the study area to estimate the temporal and spatial groundwater dynamics under the conjunctive use of groundwater and surface water. Yongji irrigation sub-area locates in the arid and semi-arid area, and it has a six months freezing and thawing period from December to May of the next year. The mechanism driving of the groundwater table change in the freezing and thawing period is different from the unfreezing period, with multiple complex impact factors. Temperature is considered as the most important factor to drive the water table change in the freezing and thawing period. An empirical model has been developed in the freezing and thawing period to correlate the groundwater table depth with the air temperature according to the measured date in the past 15 years. The model showed that the water level would drop 61.87 mm with 1℃ decline of the air temperature before 46.5 days ago. This empirical model has been integrated to a water balance model to estimate the groundwater dynamics both in the freezing and thawing period and unfreezing period. The model was then applied in the Yongji irrigation sub-area. Model parameters were calibrated with datasets from 2000 to 2010 and were validated with datasets from 2011 to 2012. Then, the calibrated model was applied to estimate the impacts of conjunctive use of groundwater and surface water under 12 kinds of water saving scenarios. The simulating results indicated that exploitation amount of available groundwater and autumn irrigation amount diverting from the Yellow river were two important factors to impact groundwater table depth. For the 12 scenarios, annual average groundwater level decline in the whole district ranges from 0.05 to 0.24 m. The value ranges of groundwater level decline from 0.16 to 0.38 m in the conjunctive groundwater and surface water irrigation district. The irrigation water diverted from Yellow river accounted for 5.7% to 15.5% of the current water diversion every year. During the unfreezing period, the recharge from irrigation contributes the largest supply to the groundwater aquifer, ranging from 1.772×108 to 2.123×108 m3/a. The recharge from precipitation ranks secondly to the aquifer with 0.267×108 m3/a. The conjunctive use of groundwater and surface water can reduce the phreatic water evaporation as 0.108×108 to 0.374×108 m3/a. The less phreatic water evaporation and re-use of groundwater were the key points of saving water by the conjunctive use of groundwater and surface water. Meanwhile, the groundwater table depth was closely related with the irrigation water amount. The relationship was described by a quadratic function which could be used as an easy groundwater predicted method when carrying out the conjunctive use of groundwater and surface water. The research results provide important reference to study the groundwater dynamics under the conjunctive use of groundwater and surface water in the similar arid and semi-arid regions.