A generalised solution for step-drawdown tests including flow dimension and elasticity

Tonder, GJ van; Botha, J. F.; Bosch, Jessica

doi:10.4314/wsa.v27i3.4978

Cited by 12 publications

(17 citation statements)

References 9 publications

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“…A recharge rate of 15 mm/year. and a pumping period of 1 year were applied, producing a sustainable yield of 0.41 L/s (or as later changed to 0.48 L/s by van Tonder et al 2001b). The result was similar to the 0.36 L/s estimated by their FC-method; except, in that case, the pumping period was assumed to be 2 years.…”

Section: Analytical Techniquessupporting

confidence: 61%

“…Using data from a test of well UO5 at an extensively monitored research test site, they conducted a numerical analysis to verify their model, where the available drawdown was related to the depth of a single, discrete horizontal fracture. Van Tonder et al (2001b) proposed that natural fractures may close over time, due to deformation of an aquifer as water levels in a well decline. Although these were comprehensive studies, no operational data were presented to confirm the researchers' estimates of long-term well yields.…”

Section: Introductionmentioning

confidence: 99%

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Reliable yields of public water-supply wells in the fractured-rock aquifers of central Maryland, USA

Hammond¹

2017

Hydrogeol J

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Most studies of fractured-rock aquifers are about analytical models used for evaluating aquifer tests or numerical methods for describing groundwater flow, but there have been few investigations on how to estimate the reliable long-term drought yields of individual hard-rock wells. During the drought period of 1998 to 2002, many municipal water suppliers in the Piedmont/Blue Ridge areas of central Maryland (USA) had to institute water restrictions due to declining well yields. Previous estimates of the yields of those wells were commonly based on extrapolating drawdowns, measured during short-term singlewell hydraulic pumping tests, to the first primary water-bearing fracture in a well. The extrapolations were often made from pseudo-equilibrium phases, frequently resulting in substantially over-estimated well yields. The methods developed in the present study to predict yields consist of extrapolating drawdown data from infinite acting radial flow periods or by fitting type curves of other conceptual models to the data, using diagnostic plots, inverse analysis and derivative analysis. Available drawdowns were determined by the positions of transition zones in crystalline rocks or thin-bedded consolidated sandstone/limestone layers (reservoir rocks). Aquifer dewatering effects were detected by type-curve matching of step-test data or by breaks in the drawdown curves constructed from hydraulic tests. Operational data were then used to confirm the predicted yields and compared to regional groundwater levels to determine seasonal variations in well yields. Such well yield estimates are needed by hydrogeologists and water engineers for the engineering design of water systems, but should be verified by the collection of longterm monitoring data.

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Section: Analytical Techniquessupporting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Reliable yields of public water-supply wells in the fractured-rock aquifers of central Maryland, USA

Hammond¹

2017

Hydrogeol J

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“…Nevertheless, the modification of Rorabaugh [1953] to account for unknown c is frequently invoked. Additionally, it is often found necessary to treat B as a function of time [ Helweg , 1994; van Tonder et al , 2001] leading to complicated overparameterized empirical functions.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Mathias et al [2008] showed that for large times, the drawdown response of a well‐being pumped at a constant rate, according to the Forchheimer equation, can be approximated by Mathias et al [2008] were only interested in Forchheimer flow to wells for constant abstraction rates and therefore did not consider SDTs or Jacob's method. However, comparison of and would suggest that (when c = 2) is a large time approximation for Forchheimer flow to a well with a piecewise constant abstraction rate, whereby Jacob's well‐loss coefficient, B , is related to the Forchheimer parameter by In this paper, following the work of Helweg [1994] and van Tonder et al [2001], it is proposed that the main shortcoming of the Jacob method is due to the assumption of a constant B coefficient. The assumption of constant B is equivalent to approximating only the large time behavior of the Forchheimer equation.…”

Section: Introductionmentioning

confidence: 99%

Step‐drawdown tests and the Forchheimer equation

Mathias

Todman

2010

Water Resources Research

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[1] Step-drawdown tests (SDTs) typically involve pumping a well at a constant rate until a quasi-steady state (QSS) is observed in the drawdown response. The well is then pumped at a higher constant rate until a new QSS is achieved. The process is repeated for additional flow rates. Analysis involves plotting the QSS drawdowns against their corresponding abstraction rates and fitting a nonlinear empirical expression. A commonly used expression, the so-called Jacob method, contains a linear "formation loss" coefficient, A, and a nonlinear "well loss" coefficient, B. In this paper, an analytical formula is derived relating B to the Forchheimer parameter. The efficiency of the Forchheimer equation for simulating SDTs is demonstrated through four case studies. Quantitative guidance is given as to when the Jacob method can be used as an accurate alternative to numerical simulation of the Forchheimer equation. Finally, the four corresponding estimates of field-scale Forchheimer parameter are implicitly compared to those obtained from smaller scale laboratory experiments. Unfortunately, the comparison remains implicit due to uncertainty associated with quantifying effective well radius and aquifer formation thickness for the SDTs.

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“…The stepwise mode of drawdown is common in the TMG sandstones and many other fractured rock aquifers in South Africa (Van Tonder et al, 2001), and is often explained as being set off by multiple boundary effects. This is true if only one flow system is intercepted by a borehole.…”

Section: Fracture Connectivity Patternmentioning

confidence: 99%

Characterisation of fracture network and groundwater preferential flow path in the Table Mountain Group (TMG) sandstones, South Africa

Li¹,

Lin²,

Xu³

2014

WSA

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Characterisation of fractured rocks and evaluation of fracture connectivity are essential for the study of subsurface flow and transport in fractured rock aquifers. In this study, we use a new method to present fracture networks and analyse the connectivity of the fractures, based on the technique of randomly-generated realisations. The application of the method aims to provide more detailed insights into the flow path and dynamics for sustainable utilisation of groundwater in the Table Mountain Group (TMG) aquifers, South Africa. Focusing on a representative wellfield in the TMG, the interpretation and integration of fracture data derived from field measurements, existing geological maps and remotely-sensed imagery, and observed responses of hydraulic tests, led to the development of a conceptual model for fracture network characterisation, which forms the basis of fracture connectivity analysis. The result shows that the a dominant number of the interconnected fractures are in the form of separated fracture clusters (networks) which is considered to be a common connectivity pattern in the TMG rocks and alike. The result also suggests that the connectivity pattern is collectively dependent on such factors as orientation, length, and density of fractures and implies that in a study domain only a small part of the fractures are responsible for flow circulation.

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A generalised solution for step-drawdown tests including flow dimension and elasticity

Cited by 12 publications

References 9 publications

Reliable yields of public water-supply wells in the fractured-rock aquifers of central Maryland, USA

Reliable yields of public water-supply wells in the fractured-rock aquifers of central Maryland, USA

Step‐drawdown tests and the Forchheimer equation

Characterisation of fracture network and groundwater preferential flow path in the Table Mountain Group (TMG) sandstones, South Africa

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