Analysis of flow processes in fractured chalk under pumped and ambient conditions (UK)

Butler, Adrian P.; Mathias, Simon A.; Gallagher, A.J.; Peach, Denis; Williams, A. T.

doi:10.1007/s10040-009-0477-4

Cited by 35 publications

(41 citation statements)

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“…The reason for this behaviour might be due to the modelling assumption of a constant vertical porosity, despite the knowledge that there can be a strongly non-linear relation between chalk transmissivity and depth. Several studies acknowledge that hydraulic conductivity in the Chalk follows a non-linear decreasing trend with depth (Allen et al, 1997;Wheater et al, 2007;Butler et al, 2009). This is mainly attributed to the decrease in fractures because of the increasing overburden and absence of water level fluctuations Butler et al, 2012).…”

Section: Performance Of the Percentile Approachmentioning

confidence: 99%

“…This is mainly attributed to the decrease in fractures because of the increasing overburden and absence of water level fluctuations Butler et al, 2012). Hydraulic conductivities in the Chalk can span several orders of magnitude (Butler et al, 2009) and are particularly enhanced at the zone of water table fluctuations . In addition, cross-flows occurring in the aquifer can lead to complicated system responses in the Chalk (Butler et al, 2009).…”

Section: Performance Of the Percentile Approachmentioning

confidence: 99%

“…Hydraulic conductivities in the Chalk can span several orders of magnitude (Butler et al, 2009) and are particularly enhanced at the zone of water table fluctuations . In addition, cross-flows occurring in the aquifer can lead to complicated system responses in the Chalk (Butler et al, 2009). For the sake of a parsimonious model structure, these characteristics were omitted in this study but their future consideration could help to improve the simulations if information about the depth profile of permeability is available.…”

Section: Performance Of the Percentile Approachmentioning

confidence: 99%

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Process-based modelling to evaluate simulated groundwater levels and frequencies in a Chalk catchment in south-western England

Brenner

Coxon

Howden

et al. 2018

Nat. Hazards Earth Syst. Sci.

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Abstract. Chalk aquifers are an important source of drinking water in the UK. Due to their properties, they are particularly vulnerable to groundwater-related hazards like floods and droughts. Understanding and predicting groundwater levels is therefore important for effective and safe water management. Chalk is known for its high porosity and, due to its dissolvability, exposed to karstification and strong subsurface heterogeneity. To cope with the karstic heterogeneity and limited data availability, specialised modelling approaches are required that balance model complexity and data availability. In this study, we present a novel approach to evaluate simulated groundwater level frequencies derived from a semi-distributed karst model that represents subsurface heterogeneity by distribution functions. Simulated groundwater storages are transferred into groundwater levels using evidence from different observations wells. Using a percentile approach we can assess the number of days exceeding or falling below selected groundwater level percentiles. Firstly, we evaluate the performance of the model when simulating groundwater level time series using a spilt sample test and parameter identifiability analysis. Secondly, we apply a split sample test to the simulated groundwater level percentiles to explore the performance in predicting groundwater level exceedances. We show that the model provides robust simulations of discharge and groundwater levels at three observation wells at a test site in a chalk-dominated catchment in south-western England. The second split sample test also indicates that the percentile approach is able to reliably predict groundwater level exceedances across all considered timescales up to their 75th percentile. However, when looking at the 90th percentile, it only provides acceptable predictions for long time periods and it fails when the 95th percentile of groundwater exceedance levels is considered. By modifying the historic forcings of our model according to expected future climate changes, we create simple climate scenarios and we show that the projected climate changes may lead to generally lower groundwater levels and a reduction of exceedances of high groundwater level percentiles.

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Section: Performance Of the Percentile Approachmentioning

confidence: 99%

Section: Performance Of the Percentile Approachmentioning

confidence: 99%

Section: Performance Of the Percentile Approachmentioning

confidence: 99%

See 1 more Smart Citation

Process-based modelling to evaluate simulated groundwater levels and frequencies in a Chalk catchment in south-western England

Brenner

Coxon

Howden

et al. 2018

Nat. Hazards Earth Syst. Sci.

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“…These models typically use data obtained from pumping test analysis, in conjunction with borehole monitoring of properties such as pressure, temperature, flow velocity, fluid electrical conductivity and tracer concentration (e.g. MacDonald & Allen 2001;Mathias et al 2007;Butler et al 2009). However, groundwater flow models based on borehole measurements can be limited by sparse data, particularly where there are significant lateral variations in hydraulic properties, or where the number of boreholes is limited for economic or environmental reasons (e.g.…”

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confidence: 99%

Measurements of spontaneous potential in chalk with application to aquifer characterization in the southern UK

Jackson

Butler

Vinogradov

2012

QJEGH

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We report the first measured values of the streaming potential coupling coefficient in chalk samples saturated with natural groundwater, and preliminary field measurements of the spontaneous potential (SP), at both ambient and pumped conditions, at a test site in the Berkshire Chalk aquifer in the southern UK. The ultimate aim of the work is to use measurements of SP, in conjunction with borehole data, to characterize groundwater flow and aquifer properties. Laboratory measurements yield a value of the streaming potential coupling coefficient of -60 ± 4 mV MPa −1 and a corresponding zeta potential of -13 ± 1 mV. A negative zeta potential contrasts with previous published open-system measurements on artificial calcite, and may reflect the presence of organic material in the natural chalk samples or HCO 3 and SO 4 ions in the groundwater. Field measurements at ambient conditions show temporal variations in SP consistent with flow processes within the aquifer, but no coherent spatial variations. Measurements during water abstraction demonstrate that voltages at the ground surface and in monitoring boreholes become more positive during pressure drawdown and more negative during pressure buildup, consistent with the negative values of streaming potential coupling coefficient and zeta potential observed in the laboratory. Moreover, the magnitude of the change in voltage is similar to that estimated using the laboratory value of the coupling coefficient. Our results suggest that measurements of SP may make a valuable contribution to characterizing groundwater flow in the UK Chalk aquifer. 2011-021r esearch-articleResearch Article45X10.1144/qjegh2011-021JacksonSpontaneous potential in chalk 2012 at

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“…Although having limited depth resolution, surface ERT monitoring has the advantage of being largely automated and minimally intrusive because electrodes only penetrate ∼20 cm below the surface and thus have insignificant influence on groundwater flow. Although the influence of boreholes, needed for hydrologic measurements and crosshole surveys, on groundwater flow often is neglected, vertical flow through open or screened wells can have important effects in highly heterogeneous or stratified media (Butler et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Imaging and quantifying salt-tracer transport in a riparian groundwater system by means of 3D ERT monitoring

et al. 2012

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Determining groundwater flow paths of infiltrated river water is necessary for studying biochemical processes in the riparian zone, but their characterization is complicated by strong temporal and spatial heterogeneity. We investigated to what extent repeat 3D surface electrical resistance tomography (ERT) can be used to monitor transport of a salt-tracer plume under close to natural gradient conditions. The aim is to estimate groundwater flow velocities and pathways at a site located within a riparian groundwater system adjacent to the perialpine Thur River in northeastern Switzerland. Our ERT time-lapse images provide constraints on the plume's shape, flow direction, and velocity. These images allow the movement of the plume to be followed for 35 m. Although the hydraulic gradient is only 1.43‰, the ERT time-lapse images demonstrate that the plume's center of mass and its front propagate with velocities of 2 × 10 −4 m∕s and 5 × 10 −4 m∕s, respectively. These velocities are compatible with groundwater resistivity monitoring data in two observation wells 5 m from the injection well. Five additional sensors in the 5-30 m distance range did not detect the plume. Comparison of the ERT time-lapse images with a groundwater transport model and time-lapse inversions of synthetic ERT data indicate that the movement of the plume can be described for the first 6 h after injection by a uniform transport model. Subsurface heterogeneity causes a change of the plume's direction and velocity at later times. Our results demonstrate the effectiveness of using timelapse 3D surface ERT to monitor flow pathways in a challenging perialpine environment over larger scales than is practically possible with crosshole 3D ERT.

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Analysis of flow processes in fractured chalk under pumped and ambient conditions (UK)

Cited by 35 publications

References 35 publications

Process-based modelling to evaluate simulated groundwater levels and frequencies in a Chalk catchment in south-western England

Process-based modelling to evaluate simulated groundwater levels and frequencies in a Chalk catchment in south-western England

Measurements of spontaneous potential in chalk with application to aquifer characterization in the southern UK

Imaging and quantifying salt-tracer transport in a riparian groundwater system by means of 3D ERT monitoring

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