海水入侵-盐渍化灾害链的水盐运移机制及电阻率判定研究

In low-lying coastal plain of fragile ecological environment area, climate change and human lead to the migration of water and salt in the aquifer, which form the seawater intrusion- soil salinization disaster chain and destroy the water and land resource. As so far, the lack of system research of connection between seawater intrusion and salinization in terms of disaster chain, especially the water and salt migration rule and mechanism in special hydrogeological condition is still existed. Therefore, laboratory and in situ simulation test combined with theoretical analysis were adopted to study the following two key issues. Firstly, the water and salt transport, accumulation and redistribution rule and the formation mechanism of seawater intrusion-soil salinization disaster chain will be analyzed by simulating the migration of water and salt under the condition in the case of low permeable lens or soil texture mutation interface, tide fluctuation, rainfall or evaporation. Secondly, the characteristics and main influence factors of the saline soil will be revealed, and the resistivity formula will be established after the resistivity test of the saline soil with water under different influence factors. As well, the resistivity response mechanism will be expounded through monitoring the resistivity variation of water and salt vertical permeability in the homogeneous soil and 3D migration in the heterogeneity soil, and the result will also be verified by in-situ test. Finally the resistivity determination method of disaster chain will be built. Project results will provide theoretical basis and technical support to quick judgement, forecasting and early warning and risk assessment of the seawater intrusion-salinization disaster chain in low-lying coastal plain.

在生态环境脆弱的海岸带低平原地区，气候变化和人类活动均会影响含水土层中水盐运移再分布过程，形成海水入侵-盐渍化灾害链，造成水土资源的破坏。目前，少有从灾害链角度分析海水入侵与盐渍化关联的研究，尤其缺乏特殊水文地质条件下的海水入侵-盐渍化灾害链发生机制及其定量判定研究。本项目拟采用室内试验、理论分析与原位测试相结合的方式，开展如下2个关键问题研究：通过水盐在土层突变或含低渗透透镜体、潮汐波动、降雨蒸发等情况下的运移模拟，分析水文条件变化时水盐在特殊地质条件下的运移规律，探讨海水入侵-盐渍化灾害链的成因机理；通过对不同影响因素下土壤电阻率的测定，建立不同水盐饱和度土壤的电阻率公式，结合水盐在垂向及三维运移电阻率响应分析和原位测试的验证，最终构建灾害链水盐运移的电阻率判定方法。项目研究成果可为滨海低平原区海水入侵-盐渍化灾害链的快速判定、预测预警与风险评估提供理论依据和技术支持。

海岸带低平原区位于陆海相互作用区，受全球气候变化和人为因素（地下水超采等）影响，海水入侵、土壤盐渍化已成为全球海岸带地区面临的主要地质灾害。两者互为因果，相互依存形成具有多重叠聚效应的灾害链。然而目前，少有从灾害链角度分析海水入侵与盐渍化关联的研究，尤其缺乏灾害链定量判定研究。本项目以灾害链的水盐运移规律及影响因素研究为理论基础，构建了不同水盐含量土壤电阻率的判定公式，设计研发了海水入侵土壤盐渍化灾害链三维监测设备，结合室内试验和原位观测开展了不同类型海岸带海水入侵-盐渍化灾害链的发生机理研究，并最终取得了一定的研究进展：（1）山东典型海水入侵-盐渍化发生区的地下水演化过程为莱州湾受卤水入侵最为明显，龙口多为现代海水入侵，而大沽河流域则主要为混合入侵；（2）饱和粉土的视电阻率与含盐量相关关系式为y=0.572x-1.06，R²=0.951，而饱和砂土的电阻率与含盐量关系式为：y = 0.492 x-0.92，R² = 0.999，同时根据电法判定原理，设计研发一套适用于海水入侵-土壤盐渍化灾害链水盐运移的三维监测设备；（3）三次的室内模拟实验表明随着水力梯度增加，入侵的速度明显加快，咸淡水过渡带的盐分含量是缓慢变化的，且过渡带的宽度与地下水运移的速度和含水介质层的渗透性有关，渗透性越低，宽度越大；运移速度越快，宽度越窄；（4）在潮汐影响下泥质潮滩表层粉土中释放的盐分远少于潜水卤水层中累积的盐分，补给潜水卤水层水体的盐源不仅来自淤泥覆盖层，还可能来自弱透水层与深层卤水层中高盐水体的越流补给，而砂质潮滩水盐运移过程与泥质潮滩的垂向运移不同，雨季的咸淡水界面并不清晰，而在旱季出现较为明显的垂向界面，并且在潮汐作用下下呈现规律性运动。项目研究成果可为滨海低平原区海水入侵-盐渍化灾害链的快速判定、预测预警与风险评估提供理论依据和技术支持。