Tidal Subsurface Analysis (TSA): Using Earth and atmospheric tides to quantify subsurface hydro-geomechanical properties

地下水资源是生态系统和人类活动的基础，但由于基流减少，地下水资源在全球范围内持续枯竭，导致水质和生态恶化，并造成地面沉降和海水入侵。准确量化地下水流量和储存变化对于实现适应性资源管理至关重要，例如通过评估过度开采的潜在影响和确定可持续产量。这就需要增加关于地下属性空间分布的知识。目前的地下水调查方法(如抽水测试)工作量大、费用高，限制了测试的速度和频率，从而造成空间上的结果有限。该项目将建立潮汐地下分析(TSA)作为一种新的方法来量化地下水文地质力学特性，如导水率、渗透率、比储存量、孔隙度、可压缩性和/或体积模数。TSA利用地下水对现有测量中包含的无处不在和可预测的地球和大气潮汐的响应。TSA将通过统一现有方法的理论来制定，这些方法已经成功地利用地下水对固体潮汐或气压负荷的响应量化了个别地下属性。下一步，将结合数值模拟和来自英国和澳大利亚地下特征良好的地点的现场数据，评估地质非均质性对使用TSA量化的属性的影响。最后，TSA将通过将每个量化的水文地质力学特性与既定的水文地质或地球物理调查技术(如抽水试验、地球物理测井或沉积物取心)得出的值进行比较来验证。由于这是一种被动的方法，它将克服主动水力地下调查固有的许多限制。预计TSA将改变地下水和大气测量的使用方式，并为监测计划、加强资源管理决策和改善欧盟水框架指令的执行增加重大价值。

Groundwater resources underpin ecosystems and human activities, yet their continued global depletion deteriorates water quality and ecology due to baseflow reduction and causes land subsidence and seawater intrusion. Accurate quantification of groundwater flow and storage changes is critical to enable adaptive resource management, for example through assessing potential impacts from over-extraction and determining sustainable yields. This necessitates an increase in knowledge of the spatial distribution of subsurface properties. Current groundwater investigation methods (e.g. pump testing) require high effort and are costly to conduct, restricting the rate and frequency of testing thus resulting in spatially limited outcomes. This project will establish Tidal Subsurface Analysis (TSA) as a novel methodology to quantify subsurface hydro-geomechanical properties such as transmissivity, permeability, specific storage, porosity, compressibility and/or bulk modulus. TSA utilises the groundwater response to the ubiquitous and predictable Earth and atmospheric tides which is contained in existing measurements. TSA will be developed by unifying the theories of existing approaches that have successfully quantified individual subsurface properties using the groundwater response to Earth tides or barometric loading. Next, the influence of geological heterogeneity on properties quantified using TSA will be evaluated using a combination of numerical modelling and field data from locations in the United Kingdom and Australia where the subsurface has been well characterised. Finally, TSA will be validated by comparing each of the quantified hydro-geomechanical properties with values derived from established hydrogeological or geophysical investigation techniques, such as pump testing, geophysical logging or sediment coring. Because it is a passive approach, it will overcome many of the limitations inherent to active hydraulic subsurface investigations. It is anticipated that TSA will shift the paradigm about how groundwater and atmospheric measurements are used and add significant value to monitoring programs, enhancing resource management decisions and improving implementation of the EU Water Framework Directive.