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，全球地下水资源的持续枯竭使水质和生态恶化，并造成地面沉降和海水入侵。准确量化地下水流量和蓄水量的变化，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。这就需要增加地下性质的空间分布的知识。目前的地下水调查方法（如水泵测试）需要付出很大的努力，成本很高，限制了测试的速度和频率，从而导致空间有限的结果。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transmittance，渗透率，特定的存储，孔隙度，压缩性和/或体积模量。TSA利用地下水对无处不在和可预测的地球和大气潮汐的响应，这些潮汐包含在现有的测量中。TSA将通过统一现有方法的理论来开发，这些方法已经成功地使用地下水对地球潮汐或气压负荷的响应来量化单个地下属性。接下来，将使用数值模拟和来自英国和澳大利亚的地下已被很好地表征的现场数据相结合，评估地质异质性对使用TSA量化的属性的影响。最后，将通过将每一个量化的水文地质力学特性与从既定的水文地质或地球物理调查技术（如水泵测试、地球物理测井或沉积物取芯）得出的值进行比较，验证TSA。 因为它是一种被动的方法，它将克服许多固有的限制，主动液压地下调查。预计TSA将改变如何使用地下水和大气测量的范式，并为监测计划增加重要价值，加强资源管理决策并改善欧盟水框架指令的实施。

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.