Matthias Raiber

Hydrochemical evolution and groundwater flow processes in the Galilee and Eromanga basins, Great Artesian Basin, Australia: a multivariate statistical approach.

The Galilee and Eromanga basins are sub-basins of the Great Artesian Basin (GAB). In this study, a multivariate statistical approach (hierarchical cluster analysis, principal component analysis and factor analysis) is carried out to identify hydrochemical patterns and assess the processes that control hydrochemical evolution within key aquifers of the GAB in these basins. The results of the hydrochemical assessment are integrated into a 3D geological model (previously developed) to support the analysis of spatial patterns of hydrochemistry, and to identify the hydrochemical and hydrological processes that control hydrochemical variability. In this area of the GAB, the hydrochemical evolution of groundwater is dominated by evapotranspiration near the recharge area resulting in a dominance of the Na-Cl water types. This is shown conceptually using two selected cross-sections which represent discrete groundwater flow paths from the recharge areas to the deeper parts of the basins. With increasing distance from the recharge area, a shift towards a dominance of carbonate (e.g. Na-HCO3 water type) has been observed. The assessment of hydrochemical changes along groundwater flow paths highlights how aquifers are separated in some areas, and how mixing between groundwater from different aquifers occurs elsewhere controlled by geological structures, including between GAB aquifers and coal bearing strata of the Galilee Basin. The results of this study suggest that distinct hydrochemical differences can be observed within the previously defined Early Cretaceous-Jurassic aquifer sequence of the GAB. A revision of the two previously recognised hydrochemical sequences is being proposed, resulting in three hydrochemical sequences based on systematic differences in hydrochemistry, salinity and dominant hydrochemical processes. The integrated approach presented in this study which combines different complementary multivariate statistical techniques with a detailed assessment of the geological framework of these sedimentary basins, can be adopted in other complex multi-aquifer systems to assess hydrochemical evolution and its geological controls.

Multivariate statistical analysis of hydrochemical data to assess alluvial aquifer–stream connectivity during drought and flood: Cressbrook Creek, southeast Queensland, Australia

A catchment-scale multivariate statistical analysis of hydrochemistry enabled assessment of interactions between alluvial groundwater and Cressbrook Creek, an intermittent drainage system in southeast Queensland, Australia. Hierarchical cluster analyses and principal component analysis were applied to time-series data to evaluate the hydrochemical evolution of groundwater during periods of extreme drought and severe flooding. A simple three-dimensional geological model was developed to conceptualise the catchment morphology and the stratigraphic framework of the alluvium. The alluvium forms a two-layer system with a basal coarse-grained layer overlain by a clay-rich low-permeability unit. In the upper and middle catchment, alluvial groundwater is chemically similar to streamwater, particularly near the creek (reflected by high HCO3/Cl and K/Na ratios and low salinities), indicating a high degree of connectivity. In the lower catchment, groundwater is more saline with lower HCO3/Cl and K/Na ratios, notably during dry periods. Groundwater salinity substantially decreased following severe flooding in 2011, notably in the lower catchment, confirming that flooding is an important mechanism for both recharge and maintaining groundwater quality. The integrated approach used in this study enabled effective interpretation of hydrological processes and can be applied to a variety of hydrological settings to synthesise and evaluate large hydrochemical datasets.RésuméUne analyse géochimique statistique multi variables à l’échelle du bassin versant a permis un diagnostic des interactions entre une nappe alluviale et Cressbrook Creek, un système de drainage intermittent en Queensland du Sud-Est, Australie. L’analyse des groupes hiérarchisés et l’analyse par composante principale ont été appliquées à des séries chronologiques de données pour évaluer l’évolution géochimique de la nappe souterraine durant des périodes de sécheresse extrême et d’inondations importantes. Un modèle géologique tridimensionnel simple été développé pour conceptualiser la morphologie du bassin versant et le cadre stratigraphique de l’alluvium. L’alluvium forme un système à deux couches avec un niveau basal à grains grossiers surmonté par un niveau riche en argile à faible perméabilité. Dans les parties supérieures et médianes du bassin versant, l’eau de l’aquifère est chimiquement similaire à l’eau de surface, particulièrement près du cours d’eau (similarité marquée par des ratios HCO3/Cl and K/Na élevés et des basses salinités), indiquant un degré de connectivité élevé. Dans la partie inférieure du bassin versant, l’eau de l’aquifère est plus saline avec des ratios HCO3/Cl and K/Na plus faibles, notamment durant les périodes de sècheresse. La salinité de la nappe a décru de façon substantielle à la suite de la crue sévère de 2011, particulièrement dans le bassin inférieur, confirmant que le ruissellement est un mécanisme important, à la fois pour la recharge et pour le maintien de la qualité de la nappe. L’approche intégrée effectuée dans cette étude a rendu possible une interprétation efficiente du processus hydrogéologique et peut être appliquée à une variété de configurations pour synthétiser et évaluer de larges ensembles de donnés hydrochimiques.ResumenUn análisis estadístico multivariado a escala de cuenca de la hidroquímica permitió la evaluación de las interacciones entre el agua subterránea aluvial y el arroyo Cressbrook, un sistema de drenaje intermitente en el sudeste de Queensland, Australia. Se aplicaron análisis de cluster jerárquico y análisis de componentes principales a series temporales de datos para evaluar la evolución hidroquímica del agua subterránea durante períodos de extremas sequías y severas inundaciones. Se desarrolló un modelo geológico tridimensional simple para conceptualizar la morfología de la cuenca y el marco estratigráfico del aluvio. El aluvio forma un sistema de dos capas con una capa basal de grano grueso cubierta por una unidad rica en arcilla de baja permeabilidad. En la cuenca superior y media, el agua subterránea aluvial es químicamente similar al agua de la corriente, particularmente cerca del arroyo (reflejado por una alta relación y una baja salinidad), indicando un alto grado de conectividad. En la cuenca inferior el agua subterránea es más salino con relaciones HCO3/Cl y K/Na más bajas, sobretodo durante períodos secos. La salinidad del agua subterránea decreció sustancialmente posteriormente a la severa inundación del 2011, sobre todo en la cuenca inferior, confirmando que la inundación es un mecanismo importante tanto para la recarga como para el mantenimiento de la calidad del agua subterránea. El enfoque integrado usado en este estudio permitió la efectiva interpretación de los procesos hidrológicos y puede ser aplicado a una variedad de configuraciones hidrológicas para sintetizar y evaluar grandes conjuntos de datos hidroquímicos.摘要本文基于水化学成分的多元统计分析, 研究地表水系与其下覆冲积含水层之间的水力联系. 采用聚类分析和主成分分析法了解极端天气(干旱及洪涝)影响下的地下水水化学成分演化规律. 研究区位于澳大利昆士兰洲东南部的Cressbrook 流域. 其地貌及地质特征被概化为三维地质模型:冲积含水层下部为粗颗粒的基岩层, 上覆泥质低渗透性岩层. 研究表明:流域的上中游, 地下水矿化度偏低, 其水化学成分表现为HCO3/Cl及K/Na 比值较高. 该特征与地表水水化学特征吻合, 反映了地表水及地下水之间的强水力联系. 流域的下游, 地下水矿化度较其上游区域偏大, HCO3/Cl 和 K/Na 比值偏低, 该特征于旱季尤为显著. 受2011年特大洪水的影响, 地下水的矿化度明显降低, 特别是下游区域. 这证明了洪水过程对地下水补给及其水化学成分的影响. 本文所采用的方法可有效且广泛地应用于水文过程调查研究.ResumoUma análise estatística multivariada de parâmetros hidroquímicos à escala de bacia permitiu deduzir as interações entre a água subterrânea aluvial e o Ribeiro de Cressbrook, um sistema de drenagem intermitente no sudeste de Queensland, Austrália. As análises grupais hierárquicas e as análises de componentes principais foram aplicadas a dados temporais sequenciais para avaliar a evolução hidroquímica da água subterrânea durante períodos de secas e inundações severas. Foi desenvolvido um modelo geológico tridimensional simples para concetualizar a morfologia da bacia e a estrutura estratigráfica da aluvião. A aluvião forma um sistema de duas camadas, com uma camada basal de granulometria grosseira coberta por uma unidade de baixa permeabilidade rica em argila. Na parte superior e intermédia da bacia a água subterrânea é quimicamente semelhante à água do curso de água superficial, particularmente nas proximidades do ribeiro (refletido pelas elevadas relações HCO3/Cl e K/Na e baixas salinidades), indicando um elevado grau de conetividade. Na parte inferior da bacia, a água subterrânea é mais salina, com relações HCO3/Cl e K/Na mais reduzidas, nomeadamente durante períodos secos. A salinidade da água subterrânea decresceu no seguimento da inundação severa de 2011, principalmente na parte mais baixa da bacia, confirmando que as inundações são um importante mecanismo tanto para a recarga como para a manutenção da qualidade da água subterrânea. A metodologia integrada usada neste estudo permitiu uma interpretação efetiva dos processos hidrológicos e pode ser aplicada a uma variedade de ambientes hidrológicos para sintetizar e avaliar grandes conjuntos de dados hidroquímicos.

Assessment of groundwater–surface water interaction using long-term hydrochemical data and isotope hydrology: Headwaters of the Condamine River, Southeast Queensland, Australia

A spatial analysis of hydrochemical data of groundwater and surface water was undertaken to identify groundwater-surface water connectivity in the headwaters of the Condamine River catchment, Southeast Queensland, Australia. An assessment of long-term hydrochemical and water level data supplemented by stable- and radioisotope measurements following a prolonged dry period dominated by baseflow, helped in determining patterns of interaction in different tributaries of the upper Condamine catchment. A conceptual hydrological model representing the major hydrochemical processes and their implications for stream-aquifer connectivity was developed and tested using multiple lines of evidence. The results of a multivariate statistical analysis highlight that there are two main regions with distinct hydrochemical facies (salinity, alkalinity, and predominant ions) in surface water. Geomorphology, geology, anthropogenic and climate influence were identified as the most relevant controlling factors of the spatial variability in water quality. Stable isotope data confirmed a clear evaporation trend in almost all surface water samples during baseflow conditions. Two water types can be identified and separated by the degree of evaporation and the proximity of one group to the local meteoric water line. The results confirm the discharge of groundwater from aquifers recharged by rainfall and located upstream of the surface water sampling sites. Overall, 222Rn data show a trend of increased activity in surface water towards the upstream portions of these tributaries, validating the use of this tracer to estimate groundwater input to the local creeks. The proportion of groundwater contribution to stream flow calculated by 222Rn and chloride mass balance is in agreement, and ranges between 20-70% in tributaries in the northern areas, and between 8-50% in the upper reaches of the main river channel. This study shows the efficacy of an integrated approach combining long-term hydrochemical data interpreted via multivariate statistics, hydraulic water level data and stable and radiogenic isotope hydrology for the determination of groundwater-surface interactions in headwater catchments.

Using 3D geological modelling and geochemical mixing models to characterise alluvial aquifer recharge sources in the upper Condamine River catchment, Queensland, Australia

The influence of mountain front recharge on the water balance of alluvial valley aquifers located in upland catchments of the Condamine River basin in Queensland, Australia, is investigated through the development of an integrated hydrogeological framework. A combination of three-dimensional (3D) geological modelling, hydraulic gradient maps, multivariate statistical analyses and hydrochemical mixing calculations is proposed for the identification of hydrochemical end-members and quantification of the relative contributions of each end-member to alluvial aquifer recharge. The recognised end-members correspond to diffuse recharge and lateral groundwater inflows from three hydrostratigraphic units directly connected to the alluvial aquifer. This approach allows mapping zones of potential inter-aquifer connectivity and areas of groundwater mixing between underlying units and the alluvium. Mixing calculations using samples collected under baseflow conditions reveal that lateral contribution from a regional volcanic aquifer system represents the majority (41%) of inflows to the alluvial aquifer. Diffuse recharge contribution (35%) and inflow from two sedimentary bedrock hydrostratigraphic units (collectively 24%) comprise the remainder of major recharge sources. A detailed geochemical assessment of alluvial groundwater evolution along a selected flowpath of a representative subcatchment of the Condamine River basin confirms mixing as a key process responsible for observed spatial variations in hydrochemistry. Dissolution of basalt-related minerals and dolomite, CO2 uptake, ion-exchange, precipitation of clay minerals, and evapotranspiration further contribute to the hydrochemical evolution of groundwater in the upland alluvial aquifer. This study highlights the benefits of undertaking an integrated approach that combines multiple independent lines of evidence. The proposed methods can be applied to investigate processes associated with inter-aquifer mixing, including groundwater contamination resulting from depressurisation of underlying geological units hydraulically connected to the shallower water reservoirs.

Tectonic control of Tertiary deposition in the Streatham Deep-Lead System in western Victoria

The mainly sub-basaltic paleodrainage of the Streatham Deep-Lead System covers >2500 km2 between the West Victorian Uplands and the Otway Basin, from which it is separated by a subsurface granite ridge. Five main tributaries flowed southwards into a series of grabens that host up to 140 m of fluvial coal-bearing sediments (Yaloak/Calivil Formation). The grabens were probably initially connected to the ocean (Otway Basin) through a western outlet; in the Eocene, the outlet shifted eastwards. Accumulation of the deep-lead sediments in the central grabens was controlled by synsedimentary subsidence along reactivated north-northwest Paleozoic and east-northeast Cretaceous faults. Fault movement occurred in the mid-Late Paleocene in the western depocentre, and Eocene in the central and eastern depocentres, and correlates well with tectonic activity in the eastern part of the Otway Basin. Following an Early Oligocene hiatus, fluvial sedimentation and syndepositional faulting recommenced from the Late Oligocene to Late Miocene/Pliocene, concomitant with sediment deposition and faulting in deep leads to the north of the divide. A final period of compressional faulting in the latest Miocene – Early Pliocene uplifted some sections of the Streatham Deep-Lead System, before it was almost entirely covered by basalt lavas.

On the effective hydraulic conductivity and macrodispersivity for density-dependent groundwater flow

In this paper, semi-analytical expressions of the effective hydraulic conductivity (

Strontium isotopes as tracers to delineate aquifer interactions and the influence of rainfall in the basalt plains of southeastern Australia

K^{E})

Environmental isotopes meet 3D geological modelling: Conceptualising recharge and structurally-controlled aquifer connectivity in the basalt plains of south-western Victoria, Australia

and macrodispersivity (