极端干旱条件下岷江上游古溪沟流域地下水-地表水环境特征及地下水资源战略储备选址适宜性评价

古溪沟流域是岷江上游汇入紫坪铺水库重要的补水单元,为研究极端干旱条件下流域内地下水-地表水化学特征和影响因素,探讨地下水资源战略储备选址适宜性,共采集16个地下水样和2个地表水样,综合运用Gibbs图、离子比值、绝对主成分-多元线性回归模型(APCS-MLR)等方法分析水化学及其影响因素;运用熵权水质指数(EWQI)进行地下水水质评价;采用层次分析法(AHP)构建流域地下水资源战略储备选址适宜性指标评价体系,探讨地下水资源战略储备选址的适宜性。结果表明,古溪沟流域地下水-地表水中主要阳离子为Ca₂₊^、M_g2+^、Na₊^、K₊^,主要阴离子为HCO_3-^、SO_42-^、Cl_-^,地下水化学类型以HCO₃-Ca、HCO₃-Ca.Mg、HCO₃.SO₄-Ca为主;Gibbs图、离子比值、APCS-MLR模型等解译出水化学组分主要来源为水-岩作用(44.08%)、工业活动(12.17%)、原生地质环境叠加工业活动(11.83%)、农业活动叠加生活污染(9.04%),水-岩相互作用主导了地下水水质形成的水文地球化学过程的同时还受到人为活动因素和自然环境等其他因素的影响;熵权水质指数(EWQI)评价地下水质量为I级和Ⅱ级分别占比56.25%和18.75%,Ⅲ级的占比为6.25%,Ⅳ级和Ⅴ级分别占比12.50%和6.25%,地表水上游为I级,下游为IV级,整体出现沿地下水径流途径,水质逐渐变差的现象,表明地下水-地表水已受到人类活动一定程度的影响;流域地下水资源战略储备选址综合适宜性指数(AI)介于1.0~9.8之间,适宜区面积占比48.57%,分布在流域中-东部下游区域,不适宜占比51.43%,不适宜区分布在流域上游区域,研究成果可在极端条件下为古溪沟流域-紫坪铺水库-都江堰的水资源安全开发利用及地下水资源战略储备选址布局提供参考。

Evaluation on the Characteristics of Groundwater Surface Water Environment and the Suitability of Groundwater Resource Strategic Reserve Site Selection in the Guxigou Basin of the Upper Reaches of the Minjiang River under Extreme Drought Conditions

The Guxigou Basin is an important water replenishment unit in the upper reaches of the Minjiang River that flows into the Zipingpu Reservoir. In order to study the characteristics and influencing factors of groundwater surface water chemistry in the basin under extreme drought conditions, and to explore the suitability of groundwater resource strategic reserve site selection, a total of 16 groundwater samples and 2 surface water samples were collected, and methods such as Gibbs plot, ion ratio, absolute principal component multiple linear regression model (APCS-MLR) were comprehensively used to analyze the hydrochemistry and its influencing factors; Using the Entropy Weighted Water Quality Index (EWQI) for groundwater quality evaluation; Using Analytic Hierarchy Process (AHP) to construct an evaluation system for the suitability of strategic reserve site selection for groundwater resources in river basins, and to explore the suitability of strategic reserve site selection for groundwater resources. The results show that the main cations in the groundwater surface water of the Guxigou Basin are Ca₂₊^{, Mg}₂₊^{, Na}₊^{, K}₊^{, and the main anions are HCO}₃-, SO_42-^{, Cl_-}. The chemical types of groundwater are mainly HCO₃-Ca, HCO₃-Ca.Mg, HCO₃.SO₄-Ca; Gibbs plots, ion ratios, APCS-MLR models, and other interpreted water chemical components mainly come from water rock interactions (44.08%), industrial activities (12.17%), superimposed industrial activities in the original geological environment (11.83%), and agricultural activities superimposed domestic pollution (9.04%). Water rock interactions lead to the hydrogeochemical process of groundwater quality formation, while also being influenced by other factors such as human activities and natural environment; The Entropy Weighted Water Quality Index (EWQI) evaluates the quality of groundwater as 56.25% and 18.75% for Class I and Class II, 6.25% for Class III, 12.50% and 6.25% for Class IV and V, respectively. The upstream of surface water is Class I, while the downstream is Class IV. The overall phenomenon of gradual deterioration of water quality along the groundwater runoff pathway indicates that groundwater surface water has been affected to a certain extent by human activities; The comprehensive suitability index (AI) of the strategic reserve site selection of groundwater resources in the basin is between 1.0 and 9.8, and the suitable area accounts for 48.57%. The suitable area is distributed in the middle east downstream area of the basin, and the unsuitable area accounts for 51.43%. The unsuitable area is distributed in the upstream area of the basin. The research results can provide a reference for the safe development and utilization of water resources in the Guxigou basin - Zipingpu reservoir - Dujiangyan Irrigation Project and the layout of the strategic reserve site selection of groundwater resources under extreme conditions.