Scale-dependent lithological variations and their control on water resources and flooding in the Eden Valley

伊甸谷(英国坎布里亚郡)遭遇了本世纪最严重的两次洪灾。它也是当地重要的水资源。伊甸河流经复杂的地质地形。它发源于湖区的火山岩，流经宾宁北部的石炭纪石灰岩，流入伊甸谷的二叠纪-三叠纪砂岩，这是一个以农村为主的地区，农业和旅游业是主要的收入来源。二叠-三叠系砂岩由彭里斯砂岩建造和舍伍德砂岩群组成，位于一个断裂带盆地(长约50公里，宽约5-15公里)，是该地区的主要含水层。然而，由于岩石的非均质性，由于原生和次生岩性的变化，它们的结构非常复杂。因此，需要更好地了解这种复杂性及其对水流的影响，以管理含水层作为水资源的潜力，并了解其在洪灾中的作用。其中一个关键部分是低渗透率特征的作用，这些特征高度依赖于规模。这包括厚厚的硅化层(二氧化硅沉积)的出现。单个单元相对较小，但可以形成厚达数十米的不连续带，绵延数公里(Fox，2016)，并影响地下水补给和水位动态(Lafare Et)。Al.，2016)。另一个重要的特征是Armathwaite堤坝，这是一种横跨整个伊甸园的火成岩入侵，似乎是各种规模地下水流动的主要障碍。随着人们对这种依赖于规模的复杂性的认识日益加深，有必要将这一知识纳入一个新的区域水文地质概念模型，该模型可以用地下水流动模型进行检验，该模型能够再现地下水位和地表水流动的响应，并为这一地质系统的管理及其在更广泛的伊甸园流域中的作用提供新的见解。这项研究的一个关键目的将是证明在不同尺度上的非均质性在控制二叠系-三叠系砂岩流动中的重要性。这不仅将提高我们对依赖于规模的地质特征和地下水响应之间关系的理解，因为它们在英国其他地方和国际上广泛存在，这项工作具有很高的可转移性。该项目的基本框架将是：-整理现有的地质数据，并与BGS地质学家合作，改进地质模型以开发水文地质概念模型；-将概念理解封装到区域和地方尺度的地下水流动数值模型中，以模拟流动过程和观测钻孔水文响应；-研究这种尺度相关的非均质性如何控制地下水流动，并影响流域内的水资源和洪水--FoxK(2016)。利用季节性趋势分解得出的概念性理解，开发了伊甸园地下水数值模型。伦敦帝国理工学院硕士论文.Lafare AEA，Peach DW&Hughes AG(2016)使用季节趋势分解来了解英国伊甸谷二叠-三叠纪砂岩含水层的地下水行为。水文地质学杂志。24(1)、141-158

The Eden Valley (Cumbria, UK) has been involved in two of the worst flooding events this century. It is also an important local water resource. The River Eden courses over a complex geological terrain. Rising on the volcanic rocks of the Lake District, it flows over the Carboniferous limestones of the north Pennines and on to the Permo-Triassic sandstones in the Vale of Eden, a largely rural area where agriculture and tourism are the main sources of income. Comprising the Penrith Sandstone Formation and the Sherwood Sandstone Group, the Permo-Triassic sandstones lie in a fault-bounded basin (approximately 50 km long and 5-15 km wide) and are the region's primary aquifers. Their structure, however, is highly complex due to the heterogeneous nature of the rocks, due to primary and secondary lithological variation. Consequently, an improved understanding of this complexity and its influence on water flow is needed to manage the aquifer's potential as a water resource, and understanding its role in flooding. A key part of this is the role of low permeability features, which are highly scale-dependent. These include the occurrence of thick silicified (depositions of silica) layers. Individual units are relatively small but can form discontinuous bands up to tens of metres thick that extend over several kilometres (Fox, 2016) and affect groundwater recharge and water level dynamics (Lafare et. al., 2016). Another important feature, the Armathwaite dyke, an igneous intrusion that crosses the entire Eden valley, appears to act as a major barrier to groundwater flow on a variety of scales. With increased awareness of this scale dependent complexity, there is a need to incorporate this knowledge into a new hydrogeological conceptual model of the region that can be tested using groundwater flow models, which are able to reproduce groundwater level and surface water flow responses and provide new insights for the management of this geological system and its role in the wider Eden valley. A key aim of the research will be to demonstrate the importance of heterogeneity at a variety of scales in controlling flow in Permo-Triassic sandstones. Not only will this improve our understanding of the relationship between scale dependent geological features and groundwater response, due to their widespread occurrence elsewhere in the UK and internationally, this work is highly transferrible. The basic outline of the project will be to:- Collate available geological data and, working with BGS geologists, enhance a geological model to develop hydrogeological conceptual models;- Encapsulate the conceptual understanding into regional and local scale numerical models of groundwater flow that simulate flow processes and observation borehole hydrograph response;- Examine how this scale-dependent heterogeneity controls groundwater flow and influences water resources and flooding in the catchment ReferencesFox K (2016). Development of a numerical groundwater model of the Eden Valley, using conceptual understanding derived from seasonal trend decomposition. MSc thesis, Imperial College London.Lafare AEA, Peach DW & Hughes AG (2016) Use of seasonal trend decomposition to understand groundwater behaviour in the Permo-Triassic Sandstone aquifer, Eden Valley, UK. Hydrogeology Journal. 24 (1), 141-158.