Eddie W. Banks

Uncertainties in vertical groundwater fluxes from 1‐D steady state heat transport analyses caused by heterogeneity, multidimensional flow, and climate change

Steady state 1-D analytical solutions to estimate groundwater fluxes from temperature profiles are an attractive option because they are simple to apply, with no complex boundary or initial conditions. Steady state solutions have been applied to estimate both aquifer scale fluxes as well as to estimate groundwater discharge to streams. This study explores the sources of uncertainty in flux estimates from regional scale aquifers caused by sensor precision, aquifer heterogeneity, multidimensional flow and variations in surface temperature due to climate change. Synthetic temperature profiles were generated using 2-D groundwater flow and heat transport models with homogeneous and heterogeneous hydraulic and thermal properties. Temperature profiles were analyzed assuming temperature can be determined with a precision between 0.1°C and 0.001°C. Analysis of synthetic temperature profiles show that the Bredehoeft and Papadopulos (1965) method can provide good estimates of the mean vertical Darcy flux over the length of the temperature profile. Reliable flux estimates were obtained when the ratio of vertical to horizontal flux was as low as 0.1, and in heterogeneous media, providing that temperature at the upper boundary was constant in time. However, temporal increases in surface temperature led to over-estimation of fluxes. Overestimates increased with time since the onset of, and with the rate of surface warming. Overall, the Bredehoeft and Papadopulos (1965) method may be more robust for the conditions with constant temperature distributions than previously thought, but that transient methods that account for surface warming should be used to determine fluxes in shallow aquifers.

Induced Temperature Gradients to Examine Groundwater Flowpaths in Open Boreholes

Techniques for characterizing the hydraulic properties and groundwater flow processes of aquifers are essential to design hydrogeologic conceptual models. In this study, rapid time series temperature profiles within open-groundwater wells in fractured rock were measured using fiber optic distributed temperature sensing (FO-DTS). To identify zones of active groundwater flow, two continuous electrical heating cables were installed alongside a FO-DTS cable to heat the column of water within the well and to create a temperature difference between the ambient temperature of the groundwater in the aquifer and that within the well. Additional tests were performed to examine the effects of pumping on hydraulic fracture interconnectivity around the well and to identify zones of increased groundwater flow. High- and low-resolution FO-DTS cable configurations were examined to test the sensitivities of the technique and compared with downhole video footage and geophysical logging to confirm the zones of active groundwater flow. Two examples are presented to demonstrate the usefulness of this new technique for rapid characterization of fracture zones in open boreholes. The combination of the FO-DTS and heating cable has excellent scope as a rapid appraisal tool for borehole construction design and improving hydrogeologic conceptual models.

Groundwater flow estimation using temperature-depth profiles in a complex environment and a changing climate

Obtaining reliable estimates of vertical groundwater flows remains a challenge but is of critical importance to the management of groundwater resources. When large scale land clearing or groundwater extraction occurs, methods based on water table fluctuations or water chemistry are unreliable. As an alternative, a number of methods based on temperature-depth (T-z) profiles are available to provide vertical groundwater flow estimates from which recharge rates may be calculated. However, methods that invoke steady state assumptions have been shown to be inappropriate for sites that have experienced land surface warming. Analytical solutions that account for surface warming are available, but they typically include unrealistic or restrictive assumptions (e.g. no flow initial conditions or linear surface warming). Here, we use a new analytical solution and associated computer program (FAST) that provides flexible initial and boundary conditions to estimate fluxes using T-z profiles from the Willunga Super Science Site, a complex, but densely instrumented groundwater catchment in South Australia. T-z profiles from seven wells (ranging from high elevation to near sea level) were utilised, in addition to mean annual air temperatures at nearby weather stations to estimate boundary conditions, and thermal properties were estimated from down borehole geophysics. Temperature based flux estimates were 5 to 23mmy-1, which are similar to those estimated using chloride mass balance. This study illustrates that T-z profiles can be studied to estimate recharge in environments where more commonly applied methods fail.

Southern South Australian groundwater microbe diversity

Groundwater is increasingly used globally for domestic, industrial and agricultural production. While many studies have focused on groundwater as a resource, the diverse ecosystems within are often ignored. Here, we assess 54 Southern South Australian groundwater microbial communities from the populated part of the state to assess their status and dynamics in isolated groundwater systems. We observed a strong site-to-site individuality in groundwater bacterial communities, likely due to the isolated nature of groundwater bodies leading to unique ecosystems. Rank abundance analysis indicates bacterial diversity is maintained even at low abundances and that the distribution fits classical ecological models for strong competition in resource-limited environments. Combined, our data indicates that despite overrepresentation of pollutant-associated bacterial orders in and around the Adelaide metropolitan area, microbial communities remain diverse and show little evidence of converging on a common pollutant-effected community.

Groundwater flow in the transition zone between freshwater and saltwater: a field-based study and analysis of measurement errors

The quantification of groundwater flow near the freshwater–saltwater transition zone at the coast is difficult because of variable-density effects and tidal dynamics. Head measurements were collected along a transect perpendicular to the shoreline at a site south of the city of Adelaide, South Australia, to determine the transient flow pattern. This paper presents a detailed overview of the measurement procedure, data post-processing methods and uncertainty analysis in order to assess how measurement errors affect the accuracy of the inferred flow patterns. A particular difficulty encountered was that some of the piezometers were leaky, which necessitated regular measurements of the electrical conductivity and temperature of the water inside the wells to correct for density effects. Other difficulties included failure of pressure transducers, data logger clock drift and operator error. The data obtained were sufficiently accurate to show that there is net seaward horizontal flow of freshwater in the top part of the aquifer, and a net landward flow of saltwater in the lower part. The vertical flow direction alternated with the tide, but due to the large uncertainty of the head gradients and density terms, no net flow could be established with any degree of confidence. While the measurement problems were amplified under the prevailing conditions at the site, similar errors can lead to large uncertainties everywhere. The methodology outlined acknowledges the inherent uncertainty involved in measuring groundwater flow. It can also assist to establish the accuracy requirements of the experimental setup.RésuméLa quantification de l’écoulement d’eaux souterraines dans la zone de transition eau douce–eau salée en zone côtière est. difficile à cause des effets d’une densité variable et de la dynamique des marées. Les mesures de charge hydraulique ont été collectées le long d’un transect perpendiculaire au trait de côte dans un site au Sud de la ville d’Adélaïde, en Australie du Sud, afin de déterminer le modèle d’écoulement transitoire. Cet article présente un aperçu détaillé de la procédure de mesures, des méthodes de post-traitement des données et de l’analyse de l’incertitude, afin d’évaluer la façon dont les erreurs de mesure affectent l’exactitude des schémas d’écoulement présumés. Une difficulté particulière rencontrée était que certains piézomètres avaient des fuites, ce qui a nécessité des mesures régulières de la conductivité électrique et de la température de l’eau dans les forages dans le but de corriger les effets de la densité. D’autres difficultés comprenaient la défaillance des capteurs de pression, la dérive de l’horloge de l’enregistreur de données et les erreurs de l’opérateur. Les données obtenues ont été suffisamment précises pour montrer qu’il y a un net écoulement horizontal de l’eau douce vers la mer dans la partie supérieure de l’aquifère et un net écoulement d’eau salée vers la terre dans la partie inférieure. La direction de l’écoulement vertical alternait avec la marée, mais en raison de la grande incertitude sur les gradients hydrauliques et le terme de densité, aucun écoulement net n’a pu être établi avec un quelconque degré de confiance. Bien que les problèmes de mesures aient été amplifiés par les conditions prévalant sur le site, des erreurs similaires peuvent conduire à de grandes incertitudes partout ailleurs. La méthodologie décrite reconnaît l’incertitude inhérente à la mesure de l’écoulement d’eaux souterraines. Elle peut aussi aider à établir les conditions de fiabilité de la mise en œuvre expérimentale.ResumenLa cuantificación del flujo de agua subterránea cerca de la zona de transición agua dulce–agua salada en la costa es difícil debido a los efectos de densidad variable y la dinámica de las mareas. Las mediciones de la carga hidráulica se tomaron a lo largo de una transecta perpendicular a la costa en un sitio al sur de la ciudad de Adelaide, en el sur de Australia, para determinar el patrón del flujo transitorio. Este trabajo presenta una descripción detallada del procedimiento de medición, los métodos de post-procesamiento de datos y el análisis de incertidumbre para evaluar cómo los errores de medición afectan la precisión de los patrones de los flujos inferidos. Una dificultad particular encontrada fue que algunos de los piezómetros tenían filtraciones, lo que requería mediciones regulares de la conductividad eléctrica y la temperatura del agua dentro de los pozos para corregir los efectos de la densidad. Otras dificultades incluyen la falla de los transductores de presión, la deriva del reloj del registrador de datos y el error del operador. Los datos obtenidos fueron lo suficientemente precisos como para mostrar que hay un flujo horizontal neto de agua dulce hacia el mar en la parte superior del acuífero, y un flujo neto hacia la tierra de agua salada en la parte inferior. La dirección del flujo vertical alternó con la marea, pero debido a la gran incertidumbre de los gradientes de la carga hidráulica y los términos de densidad, no se pudo establecer un flujo neto con ningún grado de confianza. Si bien los problemas de medición se amplificaron bajo las condiciones imperantes en el sitio, errores similares pueden conducir a grandes incertidumbres en todas partes. La metodología descripta reconoce la incertidumbre inherente involucrada en la medición del flujo del agua subterránea. También puede ayudar a establecer los requisitos de precisión para la configuración experimental.摘要由于可变密度效应和潮汐动力学,量化沿海淡水和海水过渡带附近的地下水流非常困难。收集了澳大利亚南部Adelaide市以南研究区沿垂直于海岸线断面的水头测量数据,以瞬时水流模式。本文详细论述了测量程序,数据后处理方法、不确定性分析,目的就是评价测量误差是怎样影响推测的水流模式精确度的。遇到的特别困难就是一些测压计有漏洞,迫使进行井内的电导率和水温度定期测量,针对密度效应进行纠正。其它困难包括压力传感器失效、数据记录仪移动以及操作者的误差。所获取的数据足够精确,足以显示出在含水层顶部存在着一个纯粹的向海水平淡水水流,在含水层下部存在着一个纯粹的向陆地的咸水水流。垂直水流随着潮汐变化改变方向,但是由于水头梯度和密度方面很大的不确定性,任何程度的信心都无法建立纯粹的水流。当测量问题在研究区普遍条件下被放大时,类似的误差可导致处处更大的不确定性。概述的方法认可测量地下水流中涉及到的固有不确定性。该方法也可支持建立实验机构的精确度标准。ResumoA quantificação do fluxo das águas subterrâneas próximo a zonas de transição entre água doce e salgada na costa é difícil devido aos efeitos de densidade variável e as dinâmicas das marés. Medições de carga foram coletadas ao longo de um transecto perpendicular a costa em um local ao sul da cidade de Adelaide, no sul da Austrália, para determinar o padrão de fluxo transitório. Este artigo apresenta uma visão geral detalhada do procedimento de medição, métodos de pós-processamento dos dados e análise de incerteza, para avaliar como os erros de medição afetam a acurácia dos padrões de fluxo inferidos. Uma dificuldade particular encontrada foi de que alguns dos piezômetros estavam vazando, o que exigia medições regulares da condutividade elétrica e da temperatura da água dentro dos poços para corrigir os efeitos de densidade. Outras dificuldades incluem a falha nos transdutores de pressão, desvio do relógio do datalloger e erro do operador. Os dados obtidos foram suficientemente acurados para demonstrar que há fluxo horizontal liquido de água doce em direção ao mar na parte superior do aquífero e um fluxo líquido de água salgada em direção ao continente na parte inferior. A direção do fluxo vertical alternou com a maré, mas devido à grande incerteza dos gradientes de carga e dos termos de densidade, nenhum fluxo líquido poderia ser estabelecido com qualquer grau de confiança. Enquanto os problemas de medição foram amplificados nas condições prevalecentes no local, erros similares podem levar a grandes incertezas em todos os lugares. A metodologia descrita reconhece a incerteza inerente envolvida na medição do fluxo de águas subterrâneas. Ela também pode ajudar a estabelecer os requisitos de acurácia da configuração experimental.

Hyporheic Exchange Controls Fate of Trace Organic Compounds in an Urban Stream

First-order half-lives for 26 trace organic compounds (TrOCs) were determined in the hyporheic zone (HZ) and along a 3 km reach of a first-order stream in South Australia during both dry and wet seasons. Two salt tracer experiments were conducted and evaluated using a transient storage model to characterize seasonal differences in stream residence time and transient storage. Lagrangian and time-integrated surface water sampling were conducted to calculate half-lives in the surface water. Half-lives in the HZ were calculated using porewater samples obtained from a modified mini-point sampler and hyporheic residence times measured via active heat-pulse sensing. Half of the investigated TrOCs (e.g., oxazepam, olmesartan, candesartan) were not significantly removed along both the investigated river stretch and the sampled hyporheic flow paths. The remaining TrOCs (e.g., metformin, guanylurea, valsartan) were found to be significantly removed in the HZ and along the river stretch with relative removals in the HZ correlating to reach-scale relative removals. Using the modeled transport parameters, it was estimated that wet season reach-scale removal of TrOCs was predominately caused by removal in the HZ when the intensity of hyporheic exchange was also higher. Factors that increase HZ exchange are thus likely to promote in-stream reactivity of TrOCs.

Incorporating Fault Properties in Groundwater Flow Models - Gloucester Basin NSW, Australia

More and varied resources are being discovered within our sedimentary basins including minable minerals and coal, conventional and unconventional oil and gas, geothermal energy and water resources. In addition, there is a growing need to utilize pore space for carbon storage to abate atmospheric CO2 emissions. In some regions Managed Aquifer Recharge is an important alternative to surface water storage and as mitigation to declining water levels from over extraction. These combined effects create a challenge for effective integrated basin management. Cumulative impacts can have beneficial and detrimental effects on basin resources and environmental values. Regulators and industry need to model hydrodynamic processes, history match models to monitoring bore network observations and forecast cumulative impacts at the sub-basin to basin scale. This paper explores 1) techniques for characterising fault zone dynamic properties, 2) methodologies of incorporating fault zone architecture and dynamic properties in regional groundwater flow models, and 3) ground-truthing the methodology with a case study of the highly faulted Gloucester Basin in NSW, Australia.