Pilot description and assessment : Magnesian aquifer (United Kingdom)

Mansour, Majdi ORCID: https://orcid.org/0000-0003-3058-8864; Christelis, Vasileios ORCID: https://orcid.org/0000-0003-4345-2528. 2021 Pilot description and assessment : Magnesian aquifer (United Kingdom). GeoERA, 48pp. (TACTIC Groundwater Deliverable 4.2) (Unpublished)

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Abstract/Summary

This report describes the work undertaken by the British Geological Survey (BGS/UKRI) as a part of TACTIC WP4 to calculate historical and future groundwater recharge across the outcrop of Magnesian limestone aquifer including the analysis of groundwater levels at one borehole located within this aquifer. Multiple tools, selected from the TACTIC toolbox that is developed under WP2 of the TACTIC project, have been used for this purpose. The Magnesian Limestone aquifer occupies a narrow north–south outcrop from Sunderland in the north to Nottingham to the south. The permeability of the aquifer is extremely variable due to fracturing. The Magnesian Limestone outcrop is relatively low lying but it presents an escarpment in some areas. The dominant land use is arable. At the observation borehole studied here, the aquifer is always under confined conditions. Generally the importance of the Limestone as an aquifer decreases southwards despite the existence of some abstractions Three tools have been used to estimate the recharge values. These are the lumped parameter computer model AquiMod (Mackay et al., 2014a), the transfer function-noise model Metran (Zaadnoordijk et al., 2019), and the distributed recharge model is developed ZOODRM (Mansour and Hughes, 2004). Future climate scenarios are developed based on the ISIMIP (Inter Sectoral Impact Model Inter-comparison Project (www.isimip.org) datasets. The resolution of the data is 0.5°x0.5°C global grid and at daily time steps. As part of ISIMIP, much effort has been made to standardise the climate data (e.g. bias correction). The estimation of the recharge model using the lumped model AquiMod is achieved by running the model in Monte Carlo mode. This produces many runs that are equally acceptable and consequently the uncertainty in the estimated recharge values can be assessed. The application of additional tools provides an additional mean to assess this uncertainty. Model output at the borehole studied here show a difference between the 75th and 25th percentile recharge values of approximately 36%, which indicates a relatively high degree of uncertainty. The recharge value estimated using the distributed recharge model is approximately 1.5 higher than that estimated using the lumped model. It must be noted that the distributed recharge model calculates potential recharge while the lumped model calculates actual recharge. The absolute recharge value calculated by the transfer function-noise model Metran is found to be different, more than double, from that calculated by the lumped model. Future recharge values calculated using the projected rainfall and potential evaporation values are -6.3 to 17.7% different from historical values on average. The 3o Max scenario, the wettest used in this work, produces values that are very different from the historical ones. This is observed in the output of both the lumped and the distributed models. Finally, future estimates are discussed in this report using long term average recharge values. It is recommended to carry out further analysis to these output in order to understand the temporal changes in recharge values in future, especially over the different seasons. In addition, it is recommended that the values and conclusion produced from this work should be compared to those obtained from different studies that applies future climate data obtained from different climate models.

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey, UK Research and Innovation (UKRI), European Union Horizon 2020, GeoERA
Additional Information. Not used in RCUK Gateway to Research.:	Report produced for the TACTIC Groundwater project.
Additional Keywords:	GroundwaterBGS, Groundwater
Date made live:	02 Feb 2023 10:10 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/533661

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