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Analysis of groundwater-level response to rainfall and estimation of annual recharge in fractured hard rock aquifers, NW Ireland

Cai, Zuansi; Ofterdinger, Ulrich

Authors

Ulrich Ofterdinger



Abstract

Despite fractured hard rock aquifers underlying over 65% of Ireland, knowledge of key processes controlling groundwater recharge in these bedrock systems is inadequately constrained. In this study, we examined 19 groundwater-level hydrographs from two Irish hillslope sites underlain by hard rock aquifers.
Water-level time-series in clustered monitoring wells completed at the subsoil, soil/bedrock interface, shallow and deep bedrocks were continuously monitored hourly over two hydrological years. Correlation methods were applied to investigate groundwater-level response to rainfall, as well as its seasonal variations. The results reveal that the direct groundwater recharge to the shallow and deep bedrocks on hillslope is very limited. Water-level variations within these geological units are likely dominated by slow flow rock matrix storage. The rapid responses to rainfall (62 h) with little seasonal
variations were observed to the monitoring wells installed at the subsoil and soil/bedrock interface, as well as those in the shallow or deep bedrocks at the base of the hillslope. This suggests that the direct recharge takes place within these units. An automated time-series procedure using the water-table fluctuation method was developed to estimate groundwater recharge from the water-level and rainfall data. Results show the annual recharge rates of 42–197 mm/yr in the subsoil and soil/bedrock interface, which
represent 4–19% of the annual rainfall. Statistical analysis of the relationship between the rainfall intensity and water-table rise reveal that the low rainfall intensity group (61 mm/h) has greater impact on the groundwater recharge rate than other groups (>1 mm/h). This study shows that the combination of the time-series analysis and the water-table fluctuation method could be an useful approach to investigate groundwater recharge in fractured hard rock aquifers in Ireland.

Journal Article Type Article
Acceptance Date Jan 24, 2016
Online Publication Date Feb 2, 2016
Publication Date 2016-04
Deposit Date Apr 5, 2016
Publicly Available Date Feb 3, 2017
Journal Journal of Hydrology
Print ISSN 0022-1694
Electronic ISSN 1879-2707
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 535
Pages 71-84
DOI https://doi.org/10.1016/j.jhydrol.2016.01.066
Keywords Groundwater recharge; Hard rock aquifer; Groundwater-level response time; Water-table fluctuation method
Public URL http://researchrepository.napier.ac.uk/id/eprint/9787
Publisher URL http://dx.doi.org/10.1016/j.jhydrol.2016.01.066
Contract Date Apr 5, 2016

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