利用包气带环境示踪剂评估张掖盆地降水入渗速率

降水入渗补给速率是干旱半干旱地区地下水资源评价和保护中的重要参数。长期以来在河西走廊中游盆地地下水资源评价中,一直认为地下水位埋深>5m的地带难以产生降水入渗补给。本文在黑河流域中游的张掖盆地分别选择沙丘区和裸地区,综合运用包气带同位素和水化学信息,开展了降水入渗补给研究。包气带氯质量平衡法结果表明:现代气候条件下,张掖盆地地下水位埋深>5m的地带仍存在降水入渗补给,在沙丘覆盖区,地下水位埋深6.3m时,降水入渗补给速率为13.3～14.4mm/a,入渗系数0.10～0.11;在裸地区,地下水位埋深8.6m时,降水入渗补给速率为16.8～18.4mm/a,入渗系数0.13～0.14。

Application of Unsaturated Zone Environmental Tracers to the Estimation of Rainfall Infiltrating Rate in the Zhangye Basin, Northwestern China

The rainfall infiltrating rate is a key parameter in groundwater resource assessment and groundwater protection. During the groundwater resource assessment in middle basins of the Hexi corridor in the past decades, however, the rainfall infiltration was not considered where the buried depth of the water table was more than 5 m. In the present work, the rainfall infiltration rates were estimated using chemical and isotopic information in the unsaturated zone at two sites of the Zhangye basin, which lies in the middle reaches of the Heihe River. One site is located in sand dunes in the middle of the basin and the other site is located in a wasteland area with the buried depth of the groundwater table being 8.6m. The result of chloride mass balance (CMB) indicates that there exists rainfall infiltration in Zhangye basin where the buried depth of the water table is more than 5 m. In the sand dune area, the rainfall infiltrating rate is 13.3~14.4 mm/a with the buried depth of the water table being 6.3 m, and the infiltration coefficient is about 0.10~0.11%. In the wasteland area, the rainfall infiltrating rate is 16.8~18.4 mm/a with the buried depth of the water table being 8.6m, and the infiltration coefficient is about 0.13~0.14.