Improved predictions of saturated and unsaturated zone drawdowns in a heterogeneous unconfined aquifer via transient hydraulic tomography: Laboratory sandbox experiments

Berg, Steven J.; Illman, Walter A.

doi:10.1016/j.jhydrol.2012.08.044

Cited by 21 publications

(17 citation statements)

References 46 publications

(63 reference statements)

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“…[52] As discussed by Mao et al [2011] and demonstrated in sandbox experiments by Berg and Illman [2012], impacts of variability of unsaturated parameters on the observed heads in saturated zone are insignificant. In this case, we tested this hypothesis by estimating only spatial distributions of K S and S S of the entire aquifer while keeping the effective mean values, ¼ 3.52/m and S ¼ 0.40, and ignoring their variability during the joint interpretation.…”

Section: Highly Parameterized Heterogeneous Conceptual Model (Case 2)mentioning

confidence: 99%

Joint interpretation of sequential pumping tests in unconfined aquifers

Mao

Yeh

Wan

et al. 2013

Water Resources Research

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[1] In this study, we developed a stochastic estimator for characterizing the hydraulic heterogeneity in both unsaturated and saturated zones of unconfined aquifers using transient drawdown data from sequential pumping tests. This estimator was built upon the successive linear estimator by Yeh et al. (1996), the simultaneous successive linear estimator by Xiang et al. (2009), and the 3-D finite element program for flow and transport through heterogeneous media by Srivastava and Yeh (1992). The estimator was tested afterward using simulated data sets of sequential pumping tests in a synthetic unconfined aquifer where saturated conductivity, specific storage, saturated water content, and pore-size distribution parameter vary spatially in three dimensions. Test results show that the estimator is able to produce parameter fields that capture the overall 3-D pattern of the true heterogeneous parameter fields. We subsequently validated the estimated parameter fields by assessing their ability to predict drawdowns during an independent pumping test, which was not used during the estimation phase. Results of the validation show that the predicted drawdowns based on the estimated heterogeneous parameter fields are in close agreement with the true drawdowns. In addition, predicted drawdowns based on the parameter fields from the joint interpretation are superior to those based on the parameters estimated from the homogeneous conceptual model. Lastly, while many field experiments are necessary to fully assess the robustness of this estimator and sequential pumping tests, results of this study suggest they are a promising characterization technique for unconfined aquifers.

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Section: Highly Parameterized Heterogeneous Conceptual Model (Case 2)mentioning

confidence: 99%

Joint interpretation of sequential pumping tests in unconfined aquifers

Mao

Yeh

Wan

et al. 2013

Water Resources Research

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“…The sandbox used for the validation of HT has been described in detail by Berg and Illman [2012]. Here we only provide basic information of the sandbox, various equipment, and additional work that has been completed more recently.…”

Section: Sandbox Descriptionmentioning

confidence: 99%

“…In order to characterize the hydraulic parameters, the sandbox aquifer was discretized into 3645 finite elements using variable element sizes, with an average dimension of 3 cm 3 9.4 cm 3 2.5 cm. This grid setting was kept the same with that was used in the previous THT analysis of the saturated zone of the same sandbox aquifer by Berg and Illman [2012]. The top surface of the model domain is assigned a no flow condition, since it is open to the atmosphere and no significant amount of water is gained or lost.…”

Section: Inverse Model Parametersmentioning

confidence: 99%

“…The distribution of saturated properties had been characterized by Berg and Illman [2012] through a transient HT analysis of eight pumping tests under fully saturated conditions, which can be used to obtain estimates for saturated hydraulic properties. They also obtained effective values, K eff 5 1.85 3 10 22 cm/s, S seff 5 3.94 3 10 25 /cm, through calibrating the pumping test data at port 22.…”

Section: Initial Values For K and S Smentioning

confidence: 99%

“…Mao et al [2011] subsequently used numerical examples with a variably saturated flow model [Yeh et al, 1993] to demonstrate that the role of unsaturated hydraulic parameters and their spatial variability on predicting drawdown during a pumping test. Using sandbox experiments, Berg and Illman [2012] discussed the impacts of heterogeneity information of K and S s , as well as the unsaturated zone parameters for predicting the drawdown response in an unconfined aquifer. They concluded that considering the heterogeneity of saturated zone, parameters can significantly improve the drawdown response in the saturated zone, and considering the heterogeneity of unsaturated zone, parameters yield slight improvements for the drawdown response in the unsaturated zone.…”

Section: Introductionmentioning

confidence: 99%

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Validation of hydraulic tomography in an unconfined aquifer: A controlled sandbox study

Zhao

Illman

Yeh

et al. 2015

Water Resources Research

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In this study, we demonstrate the effectiveness of hydraulic tomography (HT) that considers variably saturated flow processes in mapping the heterogeneity of both the saturated and unsaturated zones in a laboratory unconfined aquifer. The successive linear estimator (SLE) developed by Mao et al. (2013c) for interpreting HT in unconfined aquifers is utilized to obtain tomograms of hydraulic conductivity (K), specific storage (S s ), and the unsaturated zone parameters (pore size parameter (a) and saturated water content (h s )) for the Gardner-Russo's model. The estimated tomograms are first evaluated by visually comparing them with stratigraphy visible in the sandbox. Results reveal that the HT analysis is able to accurately capture the location and extent of heterogeneity including high and low K layers within the saturated and unsaturated zones, as well as reasonable distribution patterns of a and h s for the Gardner-Russo's model. We then validate the estimated tomograms through predictions of drawdown responses of pumping tests not used during the inverse modeling effort. The strong agreement between simulated and observed drawdown curves obtained by pressure transducers and tensiometers demonstrates the robust performance of HT that considers variably saturated flow processes in unconfined aquifers and the unsaturated zone above it. In addition, compared to the case using the homogeneous assumption, HT results, as expected, yield significantly better predictions of drawdowns in both the saturated and unsaturated zones. This comparison further substantiates the unbiased and minimal variance of HT analysis with the SLE algorithm.

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Impact of high‐permeability preferential flow zones on pumping‐induced airflow in unconfined aquifer

Shan

Yang

Kuang

et al. 2023

Hydrological Processes

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When the unsaturated zone of the unconfined aquifer is covered by a lowpermeability upper layer, significant airflow will be generated in the unsaturated zone during water pumping. However, high permeability preferential flow zones (PFZs) such as fractures and macropores are frequently present in the unsaturated zone, forming the preferential fluid flow paths, which may change the original airflow pattern in the unsaturated zone during the pumping test and consequently affect the precision of obtained aquifer hydraulic parameters. The main objective of this paper is to investigate the effect of PFZs in low-permeability upper layer on pumpinginduced airflow in the unsaturated zone by numerical simulations of transient threedimensional air-water two-phase flow and to quantify errors in the aquifer hydraulic parameters obtained during pumping test. The results demonstrate that a large amount of air flows quickly from the atmosphere into the unsaturated zone through the PFZs, and that the PFZs can draw some air from the nearby low-permeability soils as well. The significant influx of air through PFZs also reduces the negative air pressure in the unsaturated zone and decreases the drawdown in the saturated zone at intermediate times, which are nevertheless still greater than the results obtained in the homogeneous aquifer. Estimations of the aquifer hydraulic parameters reveal that errors of these parameters obtained are smaller when the PFZs with favourable combinations of permeability, width and quantities facilitate more air to flow into the unsaturated zone. K E Y W O R D S air-water two-phase flow, preferential flow zone, pumping test, two-phase numerical simulation, unconfined aquifer 1 | INTRODUCTION Hydraulic parameters of aquifers play an important role in the studies of hydrological modelling, climate change, and civil engineering, which include, but are not limited to, rainfall infiltration, groundwater resources utilization, groundwater impacts on the climate system, and

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Improved predictions of saturated and unsaturated zone drawdowns in a heterogeneous unconfined aquifer via transient hydraulic tomography: Laboratory sandbox experiments

Cited by 21 publications

References 46 publications

Joint interpretation of sequential pumping tests in unconfined aquifers

Joint interpretation of sequential pumping tests in unconfined aquifers

Validation of hydraulic tomography in an unconfined aquifer: A controlled sandbox study

Impact of high‐permeability preferential flow zones on pumping‐induced airflow in unconfined aquifer

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