Three-Dimensional Aquifer Heterogeneity in Pumping Test Analysis. A Numerical Investigation Using Radial Flow Models.

Mansour, Majdi; Spink, Andrew EF; Hughes, Andrew. 2006 Three-Dimensional Aquifer Heterogeneity in Pumping Test Analysis. A Numerical Investigation Using Radial Flow Models. In: MODFLOW and More 2006, Golden, Colorado, 22nd to 24th May 2006. IGWMC, Denver, Colorado, MODFLOW and More 2006: Managing Ground-Water Systems – Conference Proceedings, Poeter, Hill, & Zheng., 591-595.

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Pumping test results are often analysed on the assumption of radial symmetry. This may be because analytical solutions are used, which are limited to two-dimensional problems, or because of the widespread acceptance that this assumption is satisfactory when estimating average values of the aquifer hydraulic characteristics. A three-dimensional R-θ-Z model, built using an object-oriented approach, is used to investigate the effects of spatial heterogeneity on time-drawdown curves. Particular attention is paid to the variation of aquifer properties in the circumferential direction, a factor ignored in most pumping test analyses. The mechanisms in the numerical model include a logarithmically increasing mesh spacing in the radial direction, features operating at the pumped borehole and a moving water table. The model is applied to two and three-dimensional idealised aquifers to establish the impact of aquifer heterogeneity. Threedimensional aquifer heterogeneity is shown to produce time-drawdown curves that can be matched using two-dimensional numerical models, giving a misleading interpretation of the aquifer flow processes. For example, a delayed response to pumping at an observation borehole due to a combination of low radial permeability and a fracture in the circumferential direction can be mistaken for large aquifer storage when radial symmetry is assumed. A field example is presented where this mechanism is believed to operate.

Item Type: Publication - Conference Item (Paper)
Programmes: BGS Programmes > Groundwater Management
Additional Keywords: GroundwaterBGS, Groundwater, Groundwater modelling
NORA Subject Terms: Hydrology
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Date made live: 07 May 2010 07:15 +0 (UTC)

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