Justin F. Costelloe

Modelling the flow regime of an arid zone floodplain river, Diamantina River, Australia

Arid zone, ephemeral rivers are characterised by discharge decreasing downstream in the lower reaches due to transmission losses. Modelling the flow regime of these rivers requires data on the spatial and temporal distribution of transmission losses in these reaches. In this study, a hydrological model is developed for a 330 km reach of the Diamantina River in southwestern Queensland, where the floodplain width varies from 5 to 60 km. Analysis of gauging station data at each end of the reach indicates that transmission losses are between 70 and 98% for floods with total discharge 2300 GL. The flow routing and transmission losses are modelled using a grid-based, daily time-step conceptual model incorporating flow routing algorithms. Satellite images are used to identify the flow-paths used by the range of flood sizes and to identify threshold flow volumes for initiation of flow into new flow-paths. The grid-based approach allows for representative routing of flow through the reach and representation of spatial variability in transmission loss processes, including losses resulting from evaporation, channel/floodplain infiltration and terminal flow storage. A combination of gauging station data and satellite images is used in the calibration of the model parameters.  2003 Elsevier Science Ltd. All rights reserved.

Zooplankton diversity and assemblages in arid zone rivers of the Lake Eyre Basin, Australia

The responses of zooplankton assemblages in arid zone rivers to seasonal changes, flow events, drying and water quality changes are fundamental to our understanding of these unregulated rivers. For three years the zooplankton and littoral microfauna in three rivers in the Lake Eyre Basin were studied. A diverse assemblage was discovered with a total of 398 identifiable taxa being recorded, consisting of 72 protist, 227 rotifer and 93 microcrustacean taxa. Zooplankton diversity was highest in a boom phase during, or in the summer following, a large flood. The rotifer assemblage dominated during, or soon after, periods of flow. However, during the winter and early summer, there was a decline in rotifer taxon richness and abundance accompanied by an increase in microcrustacean taxon richness and abundance. The winter samples occurred during the recession of a large flood and the early summer samples during periods of no flow. These changes suggested the involvement of a strong annual cycle of ecosystem structure evident within the longer term patterns of boom and bust driven by the timing and size of flood events. Multivariate and regression analyses found that salinity was a significant and independent driver of assemblage composition.

Ecological risks and opportunities from engineered artificial flooding as a means of achieving environmental flow objectives

Restoration of floodplain ecosystems through the reinstatement of floods is often hampered by insufficient water as a result of competing human demands. An emerging alternative approach relies on floodplain infrastructure – such as levees, weirs, regulators, and pumps – to control water levels within floodplains without requiring landscape-scale overbank floods. This technique, albeit water efficient and capable of achieving some ecological targets, does not mimic the hydraulics, hydrodynamics, and lateral connectivity of natural floods. Engineering approaches like this may risk detrimental ecological outcomes, including reductions in biotic connectivity, river–floodplain productivity, and water quality, and thus may fail to support the range of ecological processes required to sustain healthy river–floodplain systems. Here, we review the potential benefits, risks, and mitigation options associated with engineered artificial flooding. Given the growing challenge of equitable water allocation, further research on and monitoring of engineered floods as a tool to sustain floodplain ecosystems are urgently required.

Ecological responses to variable water regimes in arid-zone wetlands: Coongie Lakes, Australia.

In dryland rivers, interactions between flow variability and complex geomorphology expose floodplain wetlands to long-term patterns of flooding and drying and highly variable short-term events. We consider whether the abundance and diversity of fish, macroinvertebrate and zooplankton communities in wetlands of the Coongie Lakes complex are influenced by long-term water regimes. To relate biological changes to changes in water regime, mean values of assemblage indices were ranked and correlated against ranked frequency of drying (i.e. water retention) in each waterbody. As water-retention time increased, fish species diversity (richness, evenness) and disease incidence rose, and fish species dominance and macroinvertebrate abundance decreased. The more mobile species of fish utilised the habitats and food resources provided by newly flooded waterbodies. We conclude that fish populations utilise wetlands with a variety of water regimes, and reductions in the frequency of inundation will decrease fish diversity with sequential losses of less mobile species.

Are alien fish disadvantaged by extremely variable flow regimes in arid-zone rivers?

The proliferation of alien fish in dryland rivers potentially obstructs the maintenance of river health. Modified flow regimes are hypothesised to facilitate invasions by alien fish but in unregulated dryland rivers, large floods provide a recruitment advantage for native over alien species whereas droughts favour alien species. We tested these hypotheses by using data from a 3-year study (2000–2003) of fish populations in the unmodified rivers of the Lake Eyre Basin (LEB) of Australia. Results from a lower reach of Cooper Creek were compared with those of an earlier study (1986–1992). During both periods, large floods occurred, with return periods ranging from >1 in 5 to >1 in 25 years. In the lower Cooper, decreases in the abundance of alien species relative to native species, and dramatic increases in recruitment of native species, were observed during a 1–3-year period following large floods. In two other rivers in 2000–2003, there was no statistically significant change in the already low abundances of alien species. We suggest that the naturally variable hydrological regimes and native-dominant fish assemblages of the unregulated LEB rivers afford some resistance to the establishment and proliferation of alien fish through flood and drought conditions.

Top-down groundwater hydrograph time-series modeling for climate-pumping decomposition

Groundwater time-series modeling has emerged as an efficient approach for simulating the impacts of multiple drivers of groundwater-head variation such as rainfall, evaporation and groundwater pumping. However, a bottom-up approach has generally been adopted whereby the input drivers have been assumed without statistical evidence for their inclusion. In this study, a parsimonious time-series model was adopted which accounts for various drivers and is able to simulate the overall groundwater-head variation. It can also separate the effects of pumping and climate drivers on multi-annual time series of groundwater-level variation. The time-series model consists of a soil-moisture layer to account for non-linearity between rainfall and recharge, as well as different pumping response functions to account for pumping from a single well, lake-induced recharge and the effects of multiple pumping bores. The method was applied to a groundwater-pumping region in south-eastern Australia. The results showed that the model is able to separate the effects of pumping from the effects of climate on groundwater-head variation. However, improved estimation of those influences requires a flexible model structure that can account for spatially varying physical processes within the study region such as the relative influence of single or multiple pumping bores and induced recharge from surface-water bodies.RésuméLa modélisation des séries temporelles de piézométrie a émergé en tant qu’approche efficace pour simuler les impacts de multiples causes de variation de la piézométrie des eaux souterraines, telles que la pluie, l’évaporation et les pompages d’eau souterraine. Cependant, une approche ascendante a généralement été adoptée en vertu de laquelle les causes d’entrée ont été supposées sans preuve statistique pour leur implication. Dans cette étude, un modèle parcimonieux de séries chronologiques a été adopté prenant en considération différentes causes et étant capable de simuler la variation piézométrique dans sa globalité. Il peut aussi séparer les effets des pompages des causes climatiques pour des séries chronologiques pluriannuelles de variation du niveau piézométrique. Le modèle de séries chronologiques consiste en une couche sol-humidité afin d’intégrer la non linéarité entre la pluie et la recharge, ainsi que différentes fonctions de réponse aux pompages pour prendre en compte le pompage dans un puits unique, la recharge induite par un lac et les effets de multiples forages d’exploitation. La méthode a été appliquée à une région d’exploitation des eaux souterraines du Sud-Est de l’Australie. Les résultats montrent que le modèle est capable de séparer les effets des pompages des effets du climat sur les variations du niveau piézométrique. Cependant, l’amélioration de l’estimation de ces influences requiert une structure de modèle flexible qui peut prendre en considération des processus physiques variant spatialement dans la région d’étude, telles que l’influence relative d’un unique ou de multiples forages d’exploitation et la recharge induite par des cours d’eau ou plans d’eau de surface.ResumenEl modelado de series de tiempo de agua subterránea se ha convertido en un enfoque eficiente para la simulación de los impactos de las múltiples causas de la variación de la carga hidráulica del agua subterránea, tales como precipitación, evaporación y bombeo de agua subterránea. Sin embargo, por lo general se ha adoptado un enfoque “de abajo a arriba” por el cual las causas de ingreso se han asumido sin evidencias estadísticas para su inclusión. En este estudio, se adoptó un modelado de series de tiempo parsimoniosas que representa a varias causas y es capaz de simular la variación global de la carga hidráulica del agua subterránea. También puede separar los efectos del bombeo y las causas climáticas en series de tiempo multianuales de variación de los niveles de agua subterránea. El modelo de series de tiempo consiste de una capa de humedad del suelo para tener cuenta la no linealidad entre la precipitación y la recarga, así como diferentes funciones de respuesta al bombeo para dar cuenta del bombeo desde un pozo único, recarga inducida por un lago y los efectos de múltiples pozos de bombeo. Se aplicó el método a una región de bombeo de agua subterránea en el sudeste de Australia. Los resultados mostraron que el modelo es capaz de separar los efectos del bombeo de los efectos de las variaciones climáticas sobre la variación de la carga hidráulica del agua subterránea. Sin embargo, una mejor estimación de esas influencias requiere una estructura de modelo flexible que puede dar cuenta de procesos físicos espacialmente variables dentro de la región de estudio, tal como la influencia relativa de simples o múltiples pozos de bombeo y recarga inducida desde cuerpos de agua superficial.摘要作为模拟地下水头变化的多重驱动因素影响一个有效的方法,地下水时序模拟应运而生,这些因素包括降雨、蒸发及地下水的抽取。然而,一种自下而上的方法普遍被采用,在这种方法中,假定输入驱动因素无其入选统计论据。在本研究中,采用了一种特别简单的时序模型,这个模型解释了各种驱动因素,能够模拟全部的地下水头变化。模型还可以区分抽水因素和气候因素对地下水位变化多个年度时序的影响。时序模型由一个解释降雨和补给之间的非线性误差的土壤水分层以及解释单井中抽水、湖泊诱发的补给及多个抽水井影响的不同抽水响应函数组成。此方法应用于澳大利亚东南部的地下水抽水区。结果显示,模型能够区分抽水和气候对地下水头变化的影响。然而,提高这些影响的估测水平需要一个切实可行的模型结构,这个模型结构要能够解释研究区内空间上变化的物理过程,诸如单个或多个钻井的相对影响及地表水体诱发的补给。ResumoA modelação de séries temporais de níveis piezométricos surgiu como uma abordagem eficiente para simular os impactes de múltiplos controladores da variação do potencial hidráulico, tais como a precipitação, a evaporação e o bombeamento da água subterrânea. No entanto, tem sido geralmente adotada uma abordagem ascendente, pela qual os controladores de entrada são assumidos sem evidência estatística da sua inclusão. Neste estudo, foi adotado um modelo parcimonioso de séries temporais que responde por vários controladores e é capaz de simular a variação global do potencial hidráulico. Também pode separar os efeitos de controladores de bombeamento e de clima em séries temporais multianuais de variação do nível piezométrico. O modelo de séries temporais é composto por uma camada de humidade do solo para explicar a não linearidade entre a precipitação e a recarga, assim como diferentes funções de resposta ao bombeamento num único furo, recarga induzida a partir de um lago e o efeito de vários furos de bombeamento. O método foi aplicado numa região de extração de água subterrânea no sudeste da Austrália. Os resultados mostraram que o modelo é capaz de separar os efeitos do bombeamento dos efeitos do clima na variação do potencial hidráulico. No entanto, a melhoria da estimativa dessas influências requer uma estrutura de modelo flexível que possa responder pela variação espacial dos processos físicos dentro da região de estudo, tais como a influência relativa de furos de bombeamento singulares ou múltiplos e a recarga induzida a partir de corpos de água superficiais.

Decomposing groundwater head variations into meteorological and pumping components: a synthetic study

Time-series modeling is often used to decompose groundwater hydrographs into individual drivers such as pumping and meteorological factors. To date, there has been an assumption that a simulation fitting the total hydrograph produces reliable estimates of the impact from each driver. That is, assessment of the decomposition has not used an independent estimate of each decomposition result. To begin to address this, a synthetic study is undertaken so that the impact of each driver is known. In this study, 500 MODFLOW groundwater models of a one-layer unconfined aquifer were constructed. For each model, three hydrogeological properties (saturated hydraulic conductivity, storativity and depth to aquifer basement), the distance between observation and pumping bores, and extraction rate were set randomly and synthetic groundwater hydrographs were derived. For each hydrograph, the influence of individual drivers was estimated using six different time-series models. These estimates were then compared to the known meteorological and pumping influences derived from the MODFLOW models. The results demonstrate that hydrograph separations obtained from time-series models do not always result in reliable estimation of pumping and meteorological influences even when the overall hydrograph fit is good. However, when the time-series model represents the important processes (e.g. phreatic evaporation is included for shallow water tables) and the (head) variance of the pumping signal to the meteorological signal is between 0.1 and 10, the time-series model has the potential to adequately separate the influence of pumping and climate.RésuméLa modélisation des séries chronologiques est souvent utilisée pour décomposer les hydrogrammes des eaux souterraines en leurs déterminants pris individuellement, par exemple le pompage et les facteurs météorologiques. Jusqu’à ce jour, il y avait une hypothèse selon laquelle une simulation qui concorde avec l’hydrogramme dans sa totalité fournit une estimation fiable de l’impact imputable à chaque déterminant. Autrement dit, l’évaluation de la décomposition n’utilisait pas une estimation indépendante de chaque résultat de décomposition. Pour avancer dans la résolution de ce problème, une étude de synthèse destinée à connaître l’impact de chaque déterminant a été entreprise. Dans cette étude, 500 modèles MODFLOW d’aquifère libre mono-couche ont été établis. Pour chaque modèle, trois propriétés hydrogéologiques (conductivité hydraulique de la zone saturée, coefficient d’emmagasinement et profondeur du mur de l’aquifère), la distance entre piézomètre et puits de pompage et le débit de pompage ont été fixés de manière aléatoire et des hydrogrammes synthétiques des eaux souterraines ont été déduits. Pour chaque hydrogramme, l’influence de chaque facteur a été estimée d’après la modélisation de six chroniques différentes. Ces évaluations ont été ensuite comparées aux influences connues de la météorologie et du pompage telles que déduites des modèles MODFLOW. Les résultats montrent que les séparations d’hydrogramme obtenues par la modélisation des séries temporelles ne se traduisent pas toujours par une estimation fiable des influences du pompage et de la météorologie, même quand la correspondance avec l’hydrogramme global est bonne. Cependant, quand le modèle des séries chronologiques représente les processus importants (par exemple l’évaporation phréatique est comptabilisée pour une surface de nappe libre peu profonde) et que la variance du signal de pompage par rapport au signal météorologique est comprise entre 0.1 et 10, le modèle de séries chronologiques est capable de séparer correctement l’influence du pompage de celle du climat.ResumenEl modelado de series de tiempo se usa a menudo para descomponer hidrogramas de agua subterránea en componentes, tales como el bombeo y los factores meteorológicos. Hasta la fecha, ha existido el supuesto que una simulación adecuada del hidrograma total produce estimaciones fiables de los efectos de cada componente. Es decir, la evaluación de la descomposición no ha utilizado una estimación independiente de cada resultado de la descomposición. Para comenzar a abordar esto, se llevó a cabo un estudio sintético de modo de conocer el impacto de cada componente. En este estudio, se construyeron 500 modelos MODFLOW de aguas subterráneas de un acuífero no confinado de una sola capa. Para cada modelo, se fijaron al azar las propiedades hidrogeológicas (conductividad hidráulica saturada, almacenamiento y profundidad al basamento acuífero), la distancia entre pozos de observación y de bombeo y la tasa de extracción y a partir de ello fueron derivados los hidrogramas sintéticos de agua subterránea. Para cada hidrograma, se estimó la influencia de los componentes individuales usando seis diferentes modelos de series de tiempo. Estas estimaciones se compararon con las influencias meteorológicas y de bombeos conocidas, derivadas a partir de los modelos MODFLOW. Los resultados demuestran que las separaciones de hidrogramas obtenidas a partir de los modelos de series de tiempo no siempre resultan en estimaciones seguras de las influencias meteorológicas y del bombeo aún cuando el ajuste general del hidrograma es bueno. Sin embargo, cuando el modelo de series de tiempo representa los procesos importantes (por ejemplo, la evaporación desde la freática es incluida para niveles freáticos someros) y la (carga hidráulica) la varianza entre la señal de bombeo y la señal meteorológica es entre 0.1 y 10, el modelo de series de tiempo tiene el potencial para separar adecuadamente la influencia de bombeo y el clima.摘要时间序列模拟常常用于分解地下水水位曲线到单个的驱动因素中,如抽水和气象因素。迄今为止,有一个假定就是,拟合整个水文曲线的模拟从每个驱动因素中可得出可靠的影响估算结果。这就是说,分解评价没有使用每个分解结果的独立估算值。为了首先强调这点,进行了综合研究,以便获知每个驱动因素的影响。在本项研究中,建立了一个单层非承压含水层500个MODFLOW地下水模型。每个模型,随机设定了三个水文地质特性(饱和水力传导系数、储存系数和含水层底部的深度)、观测井和抽水井的距离及抽水速度,得到了综合地下水水位曲线图。针对每个水位曲线图,利用六个不同的时间序列模型估算了每个驱动因素的影响。然后,把这些估算值与由MODFLOW模型得到的已知气象和抽水影响进行了对比。结果显示,即使是整体水位曲线图拟合非常好,时间序列模型得到的水位曲线图也并不总能得出抽水和气象影响的可靠估算结果。然而,当时间序列模型展示重要过程(例如,浅层水位中包括潜水蒸发)时及抽水信号对气象信号的(水头)变化在0.1和10之间时,时间序列模型具有充分分离抽水和气候影响的潜力。ResumoModelagem de séries temporais é comumente usada para decompor hidrogramas de água subterrânea em componentes forçantes individuais, como bombeamento e fatores meteorológicos. Até o momento, tem existido uma hipótese de que uma simulação que ajusta o hidrograma total produz uma estimativa confiável do impacto de cada componente. Isto é, uma avaliação de decomposição não utiliza uma estimativa independente de cada resultado da decomposição. Para começar a lidar com o problema, um estudo sintético foi feito de forma que o impacto de cada componente seja conhecido. Neste estudo, foram construídos 500 modelos de água subterrânea MODFLOW de um aquífero não confinado de uma camada. Para cada modelo, três propriedades hidrológicas (condutividade hidráulica saturada, coeficiente de armazenamento e profundidade da base do aquífero), a distância entre os poços de observação e de bombeamento e a taxa de extração foram definidas de forma aleatória, tendo seus hidrogramas de água subterrânea derivados. Para cada hidrograma, a influência das componentes forçantes individuais foi estimada usando seis modelos de séries temporais distintos. Estas estimativas foram então comparadas com influências meteorológicas e de bombeamento conhecidas, derivadas dos modelos MODFLOW. Os resultados demonstram que a separação dos hidrogramas obtidos através dos modelos de séries temporais nem sempre resultam em estimativas confiáveis da influência de bombeamento e de condições meteorológicas, mesmo quando o ajuste do hidrograma é bom. Entretanto, quando um modelo de séries temporais representa o processo importante (p. ex. evaporação freática é incluída em aquíferos rasos) e a variância (de carga) entre o sinal de bombeamento com o sinal meteorológico está entre 0.1 e 10, o modelo de séries temporais tem o potencial de separar adequadamente a influencia de bombeamento e clima.

An evaluation and regional error modeling methodology for near‐real‐time satellite rainfall data over Australia

In providing uniform spatial coverage, satellite-based rainfall estimates can potentially benefit hydrological modeling, particularly for flood prediction. Maximizing the value of information from such data requires knowledge of its error. The most recent Tropical Rainfall Measuring Mission (TRMM) 3B42RT (TRMM-RT) satellite product version 7 (v7) was used for examining evaluation procedures against in situ gauge data across mainland Australia at a daily time step, over a 9 year period. This provides insights into estimating uncertainty and informing quantitative error model development, with methodologies relevant to the recently operational Global Precipitation Measurement mission that builds upon the TRMM legacy. Important error characteristics highlighted for daily aggregated TRMM-RT v7 include increasing (negative) bias and error variance with increasing daily gauge totals and more reliability at detecting larger gauge totals with a probability of detection of <0.5 for rainfall < ~3 mm/d. Additionally, pixel location within clusters of spatially contiguous TRMM-RT v7 rainfall pixels (representing individual rain cloud masses) has predictive ability for false alarms. Differences between TRMM-RT v7 and gauge data have increasing (positive) bias and error variance with increasing TRMM-RT estimates. Difference errors binned within 10 mm/d increments of TRMM-RT v7 estimates highlighted negatively skewed error distributions for all bins, suitably approximated by the generalized extreme value distribution. An error model based on this distribution enables bias correction and definition of quantitative uncertainty bounds, which are expected to be valuable for hydrological modeling and/or merging with other rainfall products. These error characteristics are also an important benchmark for assessing if/how future satellite rainfall products have improved.

A synthetic study to evaluate the utility of hydrological signatures for calibrating a base flow separation filter

Estimation of baseflow from streamflow hydrographs has been a major challenge in hydrology for decades, leading to developments of baseflow separation filters. When without tracer or groundwater data to calibrate the filters, the standard approach to apply these filters in practice involves some degrees of subjectivity in choosing the filter parameters. This paper investigates the use of signature-based calibration in implementing baseflow filtering by testing seven possible hydrological signatures of baseflow against modelled daily baseflow produced by Li et al. [2014] for a range of synthetic catchments simulated with HydroGeoSphere. Our evaluation demonstrates that such a calibration method with few selected signatures as objectives is capable of calibrating a filter - Eckhardt filter - to yield satisfactory baseflow estimates at daily, monthly and long-term time scales, outperforming the standard approach. The best performing signatures can be readily derived from streamflow timeseries. While their performance depends on the catchment characteristics, the catchments where the signature method performs can be distinguished using commonly-used descriptors of flow dynamics. This article is protected by copyright. All rights reserved.

Soil Salinity Impacts on L-Band Remote Sensing of Soil Moisture

The recently launched Soil Moisture and Ocean Salinity (SMOS) satellite is providing soil moisture observations at continental scales by measuring L-band microwave radiation emitted from the land surface. While its retrieval algorithms will correct for factors such as vegetation and surface roughness, it will not correct for soil salinity. This letter tests the assumption that soil salinity will have a negligible impact on L-band brightness temperature (Tb) at SMOS scales using field data; airborne Tb observations were collected in a saline groundwater discharge area near Nilpinna Station, South Australia. At the 500-m scale, the airborne observations of Tb could not be reproduced using the baseline algorithm of the SMOS Level 2 retrieval scheme, without accounting for soil salinity in the model. The analysis in this letter shows that soil moisture retrieval errors of at least 0.04 m3 m-3 (i.e., the entire SMOS error budget) will occur due to salinity alone in SMOS footprints with saline coverage as low as 25% (possibly even much less). Consequently, fractional salinity coverage cannot be considered a negligible factor by microwave soil moisture satellite missions.