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New graphical methods for estimating aquifer hydraulic parameters using pumping tests with exponentially decreasing rates
Author(s) -
Zhuang Chao,
Zhou Zhifang,
Zhan Hongbin,
Wang Jinguo,
Li Yabing,
Dou Zhi
Publication year - 2019
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.13470
Subject(s) - aquifer , dimensionless quantity , drawdown (hydrology) , hydraulic conductivity , aquifer test , exponential growth , soil science , well test (oil and gas) , constant (computer programming) , mathematics , mechanics , geology , geotechnical engineering , petroleum engineering , groundwater , computer science , mathematical analysis , physics , groundwater recharge , soil water , programming language
Actual pumping tests may involve continuously decreasing rates over a certain period of time, and the hydraulic conductivity ( K ) and specific storage ( S s ) of the tested confined aquifer cannot be interpreted from the classical constant‐rate test model. In this study, we revisit the aquifer drawdown characteristics of a pumping test with an exponentially decreasing rate using the dimensionless analytical solution for such a variable‐rate model. The drawdown may decrease with time for a short period of time at intermediate pumping times for such pumping tests. A larger ratio of initial to final pumping rate and a smaller radial distance of the observation well will enhance the decreasing feature. A larger decay constant results in an earlier decrease, but it weakens the extent of such a decrease. Based on the proposed dimensionless transformation, we have proposed two graphical methods for estimating K and S s of the tested aquifer. The first is a new type curve method that does not employ the well function as commonly done in standard type curve analysis. Another is a new analytic method that takes advantage of the decreasing features of aquifer drawdown during the intermediate pumping stage. We have demonstrated the applicability and robustness of the two new graphical methods for aquifer characterization through a synthetic pumping test.