Monitoring and modeling a shallow unconfined aquifer to determine long term environmental change

Derek Clarke, Charlie Stratford, Tony Meadow, David Mercer

In the proceedings of: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: Groundwater Dependent Ecosystems 

ABSTRACT: Seasonal and long term variation in groundwater levels in an unconfined coastal aquifer near Liverpool (UK) are described. The aquifer comprises windblown sand and is 20km long, 4km wide and approximately 40m thick. Environmental managers are concerned about falling groundwater levels in several Sites of Special Scientific Interest. Groundwater has been monitored in 12 wells each month from 1972-2018 and at 30-minute intervals from 2010-2018. Figure 1. Location map and aerial view of the coastal dune system at Ainsdale (image: Google Earth) Figure 2 shows the seasonal variations measured in a typical well (ref ASDNNRW11 - circled in Figure 1). Annual rainfall at the site is 860mm/yr and Potential Evapotranspiration 550mm/yr with recharge being greatest in the months November - March. The well level data illustrates the interannual variability of groundwater levels and forcing caused by seasonal groundwater recharge. Forcing caused by climate change is less apparent. Since 1972 the mean annual air temperature has increased by 0.5oC and these has been a slow change seasonal pattern of rainfall. Winters (November-March) are 10% wetter and summers (April-October) slightly drier. Figure 2 shows a 15cm lowering of the water table levels over the 46 years of observations. This is also reflected in the trend of spring maxima and late summer minima (trend lines in Figure 2). Figure 2. Monthly observations of water table levels in well ASDNNRW11 in the sand dune aquifer at Ainsdale, 1972-2018. Reference level (0cm) is the ground surface. -150.0-140.0-130.0-120.0-110.0-100.0-90.0-80.0-70.0-60.0-50.0-40.0-30.0-20.0-10.00.010.020.030.040.050.0197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012201320142015201620172018Well 11 : Water level (cm)

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Cite this article:
Derek Clarke; Charlie Stratford; Tony Meadow; David Mercer (2018) Monitoring and modeling a shallow unconfined aquifer to determine long term environmental change in GEO2018. Ottawa, Ontario: Canadian Geotechnical Society.

@article{geo2018Paper496,author = Derek Clarke; Charlie Stratford; Tony Meadow; David Mercer,title = Monitoring and modeling a shallow unconfined aquifer to determine long term environmental change,year = 2018}