Vitaly A. Zlotnik

Stream depletion predictions using pumping test data from a heterogeneous stream - aquifer system (a case study from the Great Plains, USA)

This uniquely designed study investigates a fundamental issue—the feasibility of predicting stream depletion rates using linear uniform two-dimensional models. Required input for these models includes the hydraulic parameter estimates of the aquifer and the stream – aquifer interface, which may be obtainable through pumping test data analysis. This study utilizes pumping test data collected near the naturally meandering Prairie Creek, Platte River watershed, Nebraska, USA. Drawdown data were obtained in eight piezometer clusters, located on both sides of the stream, each containing three piezometers screened at different aquifer depths. Parameter estimates and, thus, stream depletion predictions varied over a wide range. Large parameter variance and a low degree of goodness of fit between the calculated and measured data encountered during the analysis suggest deficiencies of the uniform aquifer models in describing significant physical processes. This was also shown by additional field experiments that indicate lateral and vertical aquifer heterogeneity. Hydrogeological and sedimentological considerations of the meandering stream architecture (point bar versus cut bank) and the application of a linear piecewisehomogeneous model yielded a higher degree of goodness of fit and higher confidence in stream depletion predictions. Aquifer heterogeneity appears to be the major reason for uncertainty in stream depletion predictions, though other possible sources of uncertainty should be considered. These include the model linearity, the Dupuit assumption, the simplified representation of the stream – aquifer interface, the approximation of the stream as a straight line or a strip, and the impact of regional groundwater flow. q 2003 Elsevier B.V. All rights reserved.

Multi-level slug tests in highly permeable formations : 1. Modification of the Springer-Gelhar (SG) model

A multi-level slug test model and a method for the evaluation of vertical profiles of hydraulic conductivity in highly permeable formations are developed. A double-packer system is employed to estimate local hydraulic conductivity. Depending on the formation and double-packer system parameters, the water level recovery in the tested well can exhibit a monotonic or oscillatory response. To discern information on aquifer properties from artifacts introduced by the measurement system, the theory of flow in an aquifer and a double-packer system is developed. The mathematical model incorporates features of the Springer and Gelhar (1991) model and reduces to the Bouwer and Rice (1976) model in a special case. The model involves equations of momentum and mass conservation for the double-packer system with quasi-steady well-aquifer interaction equations. The method is uniformly applicable for both monotonic and oscillatory well responses and can produce profiles of hydraulic conductivity for the tested well. The criterion is given to determine the type of well response for given slug test conditions.

Support volume and scale effect in hydraulic conductivity: Experimental aspects

We investigate the possibility of a scale effect in hydraulic conductivity of heterogeneous aquifers using original and previously published experimental data. The evidence of scale effect is commonly based on (1) single-site, single-technique, (2) single-site, multitechnique, and (3) multisite, multitechnique approaches. Among the major conceptual problems of identification of scale effect is the difficulty quantifying the support scale for a variety of hydraulic testing techniques. Using the example of a highly heterogeneous alluvial aquifer in the Neckar River valley (Horkheimer Insel site, Germany), general guidelines for screening of field data are proposed. These guidelines are applied to the analysis of several compilations and original studies of aquifers in crystalline, argillaceous, and carbonate rocks, and in clay, till, sand, and gravel in search of scaling relationships in hydraulic conductivity. It is shown that the laboratory data on hydraulic conductivity in all types of consolidated and unconsolidated rocks are often biased toward the lower end due to problems of sampling and laboratory analysis. In addition, commonly presented in situ data from borehole tests require critical technical screening. Analysis indicates that both conceptual and technical problems obscure evidence and quantification of a possible scale effect in hydraulic conductivity. Although tremendous amounts of data are collected and published, a need still exists for systematic and conclusive analysis of these data.

Effects of Multiscale Anisotropy on Basin and Hyporheic Groundwater Flow

Various subsurface flow systems exhibit a combination of small-scale to large-scale anisotropy in hydraulic conductivity (K). The large-scale anisotropy results from systematic trends (e.g., exponential decrease or increase) of K with depth. We present a general two-dimensional solution for calculation of topography-driven groundwater flow considering both small- and large-scale anisotropy in K. This solution can be applied to diverse systems with arbitrary head distribution and geometry of the water table boundary, such as basin or hyporheic flow. In a special case, this solution reduces to the well-known Tóth model of uniform isotropic basin. We introduce an integral measure of flushing intensity that quantifies flushing at different depths. Using this solution, we simulate heads and streamlines and provide analyses of flow structure in the flow domain, relevant to basin analyses or hyporheic flow. It is shown that interactions between small-scale anisotropy and large-scale anisotropy strongly control the flow structure. In the classic Tóth flow model, the flushing intensity curves exhibit quasi-exponential decrease with depth. The new measure is capable of capturing subtle changes in the flow structure. Our study shows that both small- and large-scale anisotropy characteristics have substantial effects that need to be integrated into analysis of topography-driven flow.

Field evidence of a negative correlation between saturated hydraulic conductivity and soil carbon in a sandy soil.

] This study was performed as a part of the GrasslandDestabilization Experiment at the University of Nebraska’sBarta Brothers Ranch site (BBRS) in the eastern NSH(Figure 1), which investigates the ecological and geomor-phic stability of the NSH from an interdisciplinary perspec-tive and focuses on atmosphere–land surface–groundwaterinteractions [Wang et al., 2008]. The Nebraska Sand Hills isthe largest native grassland–stabilized sand dune area inthe Western Hemisphere and an important groundwaterrecharge source for the High Plains aquifer [Loope andSwinehart, 2000]. Mean annual temperature at the site is8.1 C and mean annual precipitation is 576 mm. About90% of the landscape at the site is composed by uplanddunes and dry interdunal areas covered by native warm-season grasslands, while the remaining 10% consists of wetmeadows and wetlands. Holocene dune sands overlie Qua-ternary and/or Pliocene alluvial sand and silt with low SOMcontent throughout the NSH.[

Boundary Conditions for Convergent Radial Tracer Tests and Effect of Well Bore Mixing Volume

Convergent radial flow tracer tests have a complex spatial nonaxial transport structure caused by the flow in the vicinity of the injection well and its finite mixing volume. The formulation of the boundary value problem, and especially the treatment of the boundary conditions at the injection well, is nontrivial. Hodgkinson and Lever [1983],Moench [1989, 1991], and Welty and Gelhar [1994] have developed different models and methods for the analysis of breakthrough curves in the extraction well. To extend interpretation techniques to breakthrough curves in the zone between injection and extraction wells, an analysis of conventional transport models is given, and improved boundary conditions are formulated for a convergent radial tracer test problem. The formulation of the boundary conditions is based upon a more detailed analysis of the kinematic flow structure and tracer mass balance in the neighborhood of the injection well. Two practical applications of revised boundary conditions for field data analysis are given. First, the note explains anomalous high well bore mixing volumes of injection wells found by Cady et al. [1993] and allows one to establish the role of mixing versus other processes (retardation, matrix diffusion, etc.). Second, it is shown that the improper use of Moenchs [1989] model can produce bias in the characteristics of breakthrough curves in the extraction well under conditions that involve a significant mixing factor in the injection well. A numerical example indicates an error in peak concentrations on a breakthrough curve by as much as 70% and in peak arrival time by 10% for Peclet numbers Pe=102. The effect becomes slightly less significant for Pe=1.

Groundwater flow near vertical recirculatory wells: effect of skin on flowgeometry and travel times with implications for aquifer remediation

Abstract Flow structure around a recirculation well in a uniform anisotropic aquifer is investigated using potential theory and Stokes’ stream function techniques. A vertical recirculation well consists of two screened sections (chambers) separated by an impermeable casing: one section extracts water from the aquifer and the other section injects the water back into the aquifer. Analytical formulae are derived for the drawdown and the stream function for a model in which the extraction and injection chambers of the well are modeled as uniformly distributed cylindrical sinks and sources, respectively. Travel times are analyzed for water particles traveling from the injection chamber to the extraction chamber along streamlines containing various percentages of the flow. We consider a disturbed zone (skin) having properties which are different from those in the uniform anisotropic aquifer owing to disturbance of the area near the well during installation. The effects of this skin on the streamlines and travel times are analyzed for various lengths separating the chambers and for various skin conductivities. The method completely eliminates the use of numerical finite-difference or finite-element methods and can be used for optimization of technological parameters in a remediation system.

Estimation of hydraulic conductivity from borehole flowmeter tests considering head losses

Abstract Recent numerical studies have demonstrated that the conventional interpretation of the borehole flowmeter test (BFT) may lead to considerable errors in estimates of the horizontal hydraulic conductivity ( K r ) due to neglect of head loss across the electromagnetic borehole flowmeter (EBF). Even in uniform aquifers, the conventional interpretation underestimates K r at the base and overestimates K r at the top of the aquifer. In this paper, we derive exact analytical solutions for hydraulic head and streamlines induced by the BFT in a confined homogeneous aquifer. The solutions explicitly consider head loss across the EBF. The derived analytical solutions for head distribution in the vicinity of the pumping well and for volumetric flux to the well sections above and below the EBF can be used to interpret field BFT data. In uniform aquifers, this approach can be applied to obtain estimates of K r from the conventional interpretation. Applications of this approach to the BFT field data set from a highly heterogeneous aquifer indicate that the constraint of aquifer homogeneity limits the applicability of this approach, but it can provide useful insights into the mechanism of flux redistribution near the borehole during the BFT.

Classification and delineation of groundwater–lake interactions in the Nebraska Sand Hills (USA) using electrical resistivity patterns

Lake–groundwater interactions exhibit a complex three-dimensional (3D) structure that is seldom studied. The utility of waterborne electrical resistivity (ER) surveys is explored for characterization of 3D groundwater flow and solute transport patterns for three lakes in the Nebraska Sand Hills, USA. Waterborne ER surveys, using contrasts between lake and groundwater solutes as natural tracers, are useful for inferring 3D patterns of groundwater flow and solute transport as well as classifying groundwater–lake interactions. Three unique groundwater flow systems are interpreted under each lake from dense networks of two-dimensional (2D) waterborne ER surveys. A lateral transition from high to low ER values beneath the saline Wilson Lake expresses its flow-through regime, where groundwater salinity indicates changes from groundwater inflow to outflow. Alkali Lake ER profiles reveal a prevalent ER increase with depth over the lakebed area that is characteristic of groundwater discharge lakes. ER profiles beneath Gimlet Lake are the most resistive and indicate pockets of high ER related to fresh groundwater discharge into the lake, supporting a flow-through regime with a short flushing time. These ER patterns correctly classify groundwater–lake interactions and provide high spatial resolution of mixing patterns for systems with varying water salinity.RésuméLes interactions eau de nappe–lac présentent une structure tridimensionnelle (3D) complexe qui est rarement étudiée. L’utilité de levers de résistivité électrique (RE) hydro portés est explorée pour caractériser un flux de nappe 3D et pour établir les caractéristiques d’écoulement de trois lacs dans les Sand Hills du Nebraska, USA. Les relevés RE hydro portés, utilisant les contrastes entre solutés du lac et solutés de l’eau souterraine en tant que traceurs naturels, sont utiles pour inférer les caractéristiques 3D du flux de nappe et transport de soluté comme pour comprendre et classer les interactions eau de nappe-lac. Trois systèmes singuliers de flux souterrains sont caractérisés sous chaque lac à partir d’un réseau dense de relevés RE 2D hydro portés. Une transition latérale de haute à basse valeur de RE sous le lac salé Wilson exprime un régime d’écoulement partagé, où la salinité de l’eau de nappe indique les changements de flux entrants et sortants. Les profils RE sur Akali Lake révèlent qu’une augmentation de RE prévaut avec la profondeur, ce qui est caractéristique des lacs de décharge de nappe. Les profils RE sous Gimlet Lake sont les plus résistants et indiquent des poches de RE élevée en relation avec une décharge d’eau douce dans le lac, siège d’un régime d’écoulement partagé avec un flux rapide. Ces caractéristiques de RE classent correctement les interactions eau de nappe– lac et fournissent en haute résolution spatiale les caractéristiques de systèmes imbriqués à eaux de salinité variable.ResumenLas interacciones entre agua subterránea–lago exhibe una estructura compleja tridimensional (3D) que raramente es estudiada. Se exploró la utilidad de los sondeos de resistividad eléctrica (ER) basados en el agua para la caracterización de los esquemas de flujo de agua subterránea 3D y de transporte de soluto para tres lagos en Nebraska Sand Hills, EEUU. Los sondeos ER basados en el agua, usando contrastes entre los solutos del agua del lago y el subterránea como trazadores naturales, son útiles para inferir esquemas 3D del flujo de agua subterránea y del transporte de solutos así como para clasificar las interacciones agua subterránea–lago. A partir de redes densas de sondeos ER basados en el agua se interpretaron tres sistemas únicos de flujo de agua subterránea bajo de cada lago. Una transición lateral desde altos a bajos valores debajo del lago salino Wilson expresa su régimen de flujo continuo a través del medio, donde la salinidad del agua subterránea indica cambios desde la entrada de agua subterránea hasta su salida. Los perfiles ER del lago Alkali revelan un predominio de incremento de ER con la profundidad sobre el área del lecho del lago que es característico de lagos de descarga de agua subterránea. Los perfiles ER debajo del lago Gimlet son los más resistivos e indican bolsas de alta ER relacionados a la descarga de agua subterránea dulce en el lago, manteniendo un régimen continuo de flujo con un tiempo corto de lavado. Estos esquemas de ER clasifican correctamente las interacciones lago–agua subterránea y proporcionan una alta resolución espacial de los esquemas de mezcla para sistemas con salinidades del agua variables.摘要湖水地下水相互作用显示为一种复杂的、很少被研究过的三维结构。本文在美国内布拉斯加州沙丘开展了水上电阻率(ER)调查以刻画三个湖泊的三维地下水流和溶质运移特征。水上ER调查是利用湖水和地下水溶质的差异作为天然示踪剂,在推断地下水流和溶质运移的三维形态以及划分地下水湖水相互作用方面非常有用。通过高密度2维水上ER调查,在每个湖泊下面解译出了3种独立的地下水流系统。在Wilson咸湖下面ER值从高到低的侧向过渡,显示了它的水流动态,在这里用地下水盐度指示地下水流入到流出的变化。Alkali湖ER剖面显示出在湖床上ER随深度增加而升高的趋势,为地下水向湖排泄的特征。Gimlet湖的ER剖面电阻率最高,高ER区与地下淡水向湖的排泄有关,支持短时间内水流通过的推断。ER的分布特征恰当准确的划分了地下水湖水相互作用,且提供了高空间分辨率的不同盐度的地下水混合形态特征。ResumoAs interações lago–água subterrânea exibem uma complexa estrutura tri-dimensional (3D) que é frequentemente estudada. A utilidade de campanhas de resistividade elétrica (RE) em meio aquoso é explorada para caraterizar o fluxo subterrâneo 3D e os padrões de transporte de solutos em três lagos nas Montanhas de Nebraska Sand, EUA. As campanhas de RE em meio aquoso, usando os contrastes entre a concentração de solutos do lago e da água subterrânea como traçadores naturais, são úteis para inferir os padrões 3D do fluxo subterrâneo e transporte de solutos, bem como para classificar as interações água subterrânea-lago. A partir de densas redes de campanhas de RE 2D em meio aquoso, foram interpretados três sistemas únicos de fluxo subterrâneo subjacentes a cada lago. A transição lateral de elevados valores para baixos valores de RE debaixo do lago salino de Wilson reflete o seu regime de passagem de água, onde a salinidade da água subterrânea indica mudanças entre entradas e saídas de água subterrânea. Os perfis de RE do Lago Alkali revelam a prevalência de um aumento da RE com a profundidade ao longo da área do leito do lago, o que é caraterístico de lagos com descarga de água subterrânea. Os perfis de RE debaixo do Lago Gimlet são os mais resistivos e indicam a existência de zonas com elevada RE, relacionadas com a descarga de água doce subterrânea no lago, o que reflete um regime de passagem de água com um curto período de renovação. Estes padrões de RE permitem classificar corretamente as interações água subterrânea–lago e fornecem uma elevada resolução espacial dos padrões de mistura em sistemas com águas de diferentes salinidades.

Jurassic earthquake sequence recorded by multiple generations of sand blows, Zion National Park, Utah

Earthquakes along convergent plate boundaries commonly occur in sequences that are complete within 1 yr, and may include 8–10 events strong enough to generate sand blows. Dune crossbeds within the Jurassic Navajo Sandstone of Utah (western United States) enclose intact and truncated sand blows, and the intrusive structures that fed them. We mapped the distribution of more than 800 soft-sediment dikes and pipes at two small sites. All water-escape structures intersect a single paleo-surface, and are limited to the upper portion of the underlying set of cross-strata and the lower portion of the overlying set. A small portion of one set of crossbeds that represents ∼1 yr of dune migration encloses eight generations of eruptive events. We interpret these superimposed depositional and deformational structures as the record of a single shock-aftershock earthquake sequence. The completeness and temporal detail of this paleoseismic record are unique, and were made possible when sand blows repeatedly erupted onto lee slopes of migrating dunes. Similar records should be sought in modern dunefields with shallow water tables.