The daily groundwater level (GWL) response in the Permo-Triassic Sandstone aquifers in the Eden Valley, England (UK), has been studied using the seasonal trend decomposition by LOESS (STL) technique. The hydrographs from 18 boreholes in the Permo-Triassic Sandstone were decomposed into three components: seasonality, general trend and remainder. The decomposition was analysed first visually, then using tools involving a variance ratio, time-series hierarchical clustering and correlation analysis. Differences and similarities in decomposition pattern were explained using the physical and hydrogeological information associated with each borehole. The Penrith Sandstone exhibits vertical and horizontal heterogeneity, whereas the more homogeneous St Bees Sandstone groundwater hydrographs characterize a well-identified seasonality; however, exceptions can be identified. A stronger trend component is obtained in the silicified parts of the northern Penrith Sandstone, while the southern Penrith, containing Brockram (breccias) Formation, shows a greater relative variability of the seasonal component. Other boreholes drilled as shallow/deep pairs show differences in responses, revealing the potential vertical heterogeneities within the Penrith Sandstone. The differences in bedrock characteristics between and within the Penrith and St Bees Sandstone formations appear to influence the GWL response. The de-seasonalized and de-trended GWL time series were then used to characterize the response, for example in terms of memory effect (autocorrelation analysis). By applying the STL method, it is possible to analyse GWL hydrographs leading to better conceptual understanding of the groundwater flow. Thus, variation in groundwater response can be used to gain insight into the aquifer physical properties and understand differences in groundwater behaviour.

The calculation of distributed recharge is necessary to drive numerical groundwater models used to manage and protect groundwater resources, to assess the impact of anthropogenic stresses and climate change, and to study the viability of technologies, such as exploiting the heat stored in the ground. A national-scale model allows policymakers and governmental decision-makers to set policy within the correct geographical context. However, many challenges are associated with building large-scale models, for example, the representation of processes on coarse grid resolution. This study presents distributed potential recharge values, calculated using the modified Environment Agency (EA)/Food and Agriculture Organization recharge algorithm. The model calibration is presented and the simulated potential recharge values and soil moisture deficit values are compared with estimates provided by the EA and the Meteorological Office (Met Office). Long-term average potential recharge values are very small in the east of the UK but they increase significantly towards the west and north, reaching values as high as 8 mm day ⁻¹ over the hills of Wales and Scotland. While this study highlights the need for further model refinement, the presented results are useful for assessing the potential recharge values at a national scale and for undertaking water resource studies, especially in catchments with unconfined/near-surface aquifers.