Theory of flow in unconfined aquifers considering delayed response of the water table

Abstract

A new analytical model is proposed for the delayed response process characterizing flow to a well in an unconfined aquifer. The present approach differs from that of Boulton [1954b, 1963, 1970] and Boulton and Pontin [1971] in that it is based only on well‐defined physical parameters of the aquifer system. Therefore it provides a possible physical explanation for the mechanism of delayed water table response and eliminates the conceptual difficulties encountered with Boulton's theory of ‘delayed yield from storage above the water table.’ Contrary to prevailing belief the process of delayed response in a homogeneous anisotropic phreatic aquifer can be simulated by using constant values of specific storage and specific yield without recourse to unsaturated flow theory. The results suggest that, in the absence of significant infiltration at the ground surface, compressibility may often be a much more important factor than unsaturated flow above the water table. Current methods of analyzing field data from unconfined aquifers do not usually consider compressibility. The present theory shows that such methods are limited in their application to relatively large values of time.

Joint interpretation of sequential pumping tests in unconfined aquifers

“…Traditional characterization approaches have adopted homogeneous conceptual models that assume aquifer homogeneity and have attempted to derive effective hydraulic parameters based on drawdowns from a single pumping test, for example, those by Theis [1935] and Cooper and Jacob [1946] for confined aquifers and those by Boulton [1963], Dagan [1967], Brutsaert [1970], Streltsova [1972aStreltsova [ , 1972b, Neuman [1972], Lakshminarayana and Rajagopalan [1978], Moench [1995], Mathias and Butler [2006], and Mishra and Neuman [2010] for unconfined aquifers. Recent numerical, sandbox, and field experiments by Wu et al [2005], Straface et al [2007], Xiang et al [2009], Wen et al [2010], Huang et al [2011], and Berg and Illman [2011b] however questioned the representativeness of the estimates from these conventional approaches.…”

Investigation of Hexavalent Chromium Flux to Groundwater at the 100-C-7:1 Excavation Site

“…Hydraulic properties were estimated using a type-curve fitting method according to the analytical solution of Neuman (1972Neuman ( , 1974Neuman ( , 1975 for an unconfined aquifer with delayed gravity response (specific yield). In this analysis, the wells can be either partially or fully penetrating.…”

Evaluation of the streambed leakage concept in analytical models using data from three pumping tests

“…In this study, the term aquifer storativity refers to the specific yield of the aquifer material, because the models were applied only to the late time drawdown data (e.g. Neuman 1972).…”