Analysis of the impact of hydraulic properties and climate change on estimations of borehole yields

Ascott, Matthew J.; Mansour, Majdi; Bloomfield, John P. ORCID: https://orcid.org/0000-0002-5730-1723; Upton, Kirsty A.. 2019 Analysis of the impact of hydraulic properties and climate change on estimations of borehole yields. Journal of Hydrology, 577, 123998. 10.1016/j.jhydrol.2019.123998

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Abstract/Summary

Understanding the impact of climate change on borehole yields from fractured aquifers is essential for future water resources planning and management. Although variation in hydraulic conductivity with depth (VKD) in fractured aquifers is a well-known phenomenon, the relative significance of climate change and VKD on borehole yield estimates is poorly understood. We hypothesize that VKD exerts a significant additional control on borehole yields under climate change that has not been considered in yield assessments to date. We developed a simple two-layered radial groundwater flow model of an idealised pumping borehole in the fractured Chalk aquifer of south-east England, and applied 11 VKD profiles based on a simple conceptual representation of variability in hydraulic conductivity with depth in the Chalk. For each time step, the transmissivity is calculated by integrating the hydraulic conductivity VKD profile over the saturated depth calculated at the previous time step. For each VKD and resulting transmissivity, we applied 20 climate scenarios and six constant pumping rates for the period 1962 – 2014. We then estimated borehole yields based on the derived lowest pumping water levels during key drought years (e.g. 1976). We show that the hydraulic properties of the aquifer are more significant (p < 0.001) than changes in climate (p > 0.1) in controlling lowest pumping groundwater levels when abstraction rates are < 9000 m3/day, and that both are significant when abstraction ≥ 9000 m3/day. Hydraulic conductivity is as significant a control as climate on borehole yields, although responses are non-linear associated with whether pumping water level-pumping rate curves intersect key yield constraints (e.g. pump intake depth, major inflow horizons). It is recommended that variations in hydraulic conductivity with depth are taken into consideration in future assessments of borehole yields under climate change. The approach presented is generic and can be applied across different aquifers where vertical heterogeneity is present and affects transmissivity.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.jhydrol.2019.123998
ISSN:	00221694
Additional Keywords:	GroundwaterBGS, Groundwater, Groundwater resources, Aquifer characterisation, Climate change
Date made live:	20 Aug 2019 13:48 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/524818

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