区域性地下水流河谷区排泄咸淡混合特征分析

西南高山峡谷区,地形及地层岩性特征造就了温度、矿化度异于局部地下水流系统的区域地下水流系统,季节变动或人为因素造成地表水水位抬升甚至淹没地下水的排泄点,从而影响该系统排泄端地下水与地表水的混合特征。为了研究该区域的地下水流和地表水的盐分混合特征,采用砂槽物理模型以及SEAWAT模块数值模型从盐分浓度分布特征方面研究排泄端混合特征的变化规律。结果表明:区域地下水流系统与地表水之间存在水头差与密度差,在二者共同作用下,淡水侵入含水层,发生水动力弥散作用,形成低矿化度淡水逐渐过渡到高矿化度咸水的混合过渡带,其边界呈抛物线形;通过模拟不同密度差条件下的混合过程,进一步表明咸淡水密度差越大,混合过渡带后退距离越远,形态越扁长。研究结果将为分析咸淡水混合过程中温度分布特征提供参考,进而为深入研究西南地区多级次地下水流系统的混合特征作铺垫。

Characteristics of the Mix Between Salt Water and Fresh Water in Regional Groundwater Discharging Area of Valleys

On the account of topography and strata of mountains and valleys in Southwest China, the temperature and salinity of regional groundwater system are different from those of local flow system. Induced by climate change or human behaviors,surface water level rises and even inundates the discharge point of groundwater, exerting im-pact on the mix between groundwater and surface water in the regional discharging area.In the present paper,varia-tions in the features of the mix between salt water and fresh water flows are researched via sand box physical model and SEAWAT simulation from the aspect of salinity distribution. The results are concluded as follows:under the ac-tions of both hydraulic head difference and density difference between regional groundwater and surface water, a mixed transition zone(from low salinity water to high salinity water) with parabolic boundary is generated by hydro-dynamic dispersion by the intrusion of fresh water into aquifer.Furthermore,simulations of the mix between salt wa-ter and saline water with density difference demonstrate that when the density difference gets larger, the backward distance of the mixed transition zone is longer,and the boundary is more prolate. The research results lay a founda-tion for deep research on the mix characteristics between different levels of groundwater systems in Southwest China.