Rebecca Doble

An Analysis of River Bank Slope and Unsaturated Flow Effects on Bank Storage

Recognizing the underlying mechanisms of bank storage and return flow is important for understanding streamflow hydrographs. Analytical models have been widely used to estimate the impacts of bank storage, but are often based on assumptions of conditions that are rarely found in the field, such as vertical river banks and saturated flow. Numerical simulations of bank storage and return flow in river-aquifer cross sections with vertical and sloping banks were undertaken using a fully-coupled, surface-subsurface flow model. Sloping river banks were found to increase the bank infiltration rates by 98% and storage volume by 40% for a bank slope of 3.4° from horizontal, and for a slope of 8.5°, delay bank return flow by more than four times compared with vertical river banks and saturated flow. The results suggested that conventional analytical approximations cannot adequately be used to quantify bank storage when bank slope is less than 60° from horizontal. Additionally, in the unconfined aquifers modeled, the analytical solutions did not accurately model bank storage and return flow even in rivers with vertical banks due to a violation of the dupuit assumption. Bank storage and return flow were also modeled for more realistic cross sections and river hydrograph from the Fitzroy River, Western Australia, to indicate the importance of accurately modeling sloping river banks at a field scale. Following a single wet season flood event of 12 m, results showed that it may take over 3.5 years for 50% of the bank storage volume to return to the river.

Groundwater recharge from overbank floods

[1]xa0Overbank flood recharge is increasingly acknowledged as important for estimations of aquifer sustainable yield. The physics of this process in areas with shallow groundwater, however, is not well understood and typically is not included in river or groundwater models. Modeling of the overbank flood recharge process was undertaken using a fully coupled, surface-subsurface flow model to compare the volume of infiltration through a floodplain with varying surface sediment, aquifer, and flood parameters. The infiltration volume was found to increase with the conductance of the clogging layer (represented by a thin veneer of sediments across the floodplain and river bed), flood wave height, peak duration, and aquifer transmissivity and to decrease with increasing water table gradient (positive toward the river). The influence of the flood wave and aquifer hydraulic parameters was more pronounced in systems with sand or loam clogging layers. Irregularities in floodplain elevation had a large effect on infiltration volume. A dimensionless analysis of the flood recharge process identified the factors that limited flood infiltration for each of the modeled scenarios: the clogging layer conductance, unsaturated aquifer storage, or aquifer transmissivity. A dimensionless numberF* was used to predict the limiting factor in floodplain systems. An analytical equation was developed to estimate the infiltration volume for catchments where full numerical modeling is not warranted or applicable. Results from the analytical equation compared favorably with recharge modeled using a more complex numerical model.

Review: Current and emerging methods for catchment-scale modelling of recharge and evapotranspiration from shallow groundwater

A review is provided of the current and emerging methods for modelling catchment-scale recharge and evapotranspiration (ET) in shallow groundwater systems. With increasing availability of data, such as remotely sensed reflectance and land-surface temperature data, it is now possible to model groundwater recharge and ET with more physically realistic complexity and greater levels of confidence. The conceptual representation of recharge and ET in groundwater models is critical in areas with shallow groundwater. The depth dependence of recharge and vegetation water-use feedback requires additional calibration to fluxes as well as heads. Explicit definition of gross recharge vs. net recharge, and groundwater ET vs. unsaturated zone ET, in preparing model inputs and reporting model results is necessary to avoid double accounting in the water balance. Methods for modelling recharge and ET include (1) use of simple surface boundary conditions for groundwater flow models, (2) coupling saturated groundwater models with one-dimensional unsaturated-zone models, and (3) more complex fully-coupled surface-unsaturated-saturated conceptualisations. Model emulation provides a means for including complex model behaviours with lower computational effort. A precise ET surface input is essential for accurate model outputs, and the model conceptualisation depends on the spatial and temporal scales under investigation. Using remote sensing information for recharge and ET inputs in model calibration or in model–data fusion is an area for future research development. Improved use of uncertainty analysis to provide probability bounds for groundwater model outputs, understanding model sensitivity and parameter dependence, and guidance for further field-data acquisition are also areas for future research.RésuméUne analyse des méthodes courantes et émergentes pour la modélisation de la recharge à l’échelle de bassin versant et de l’évapotranspiration (ET) dans des systèmes aquifères peu profonds est fournie. Avec l’augmentation de la disponibilité des données, telles que des données de réflectance et de température de surface terrestre par télédétection, il est maintenant possible de modéliser la recharge des eaux souterraines et ET avec une prise en compte plus réaliste de la complexité physique et avec des niveaux plus élevés de confiance. La représentation conceptuelle de la recharge et d’ET dans les modèles d’eaux souterraines est critique dans les zones avec des eaux souterraines à faible profondeur. La dépendance de la profondeur de la recharge et la rétroaction de l’utilisation de l’eau par la végétation nécessitent un étalonnage supplémentaire pour les flux ainsi que pour les charges hydrauliques. Une définition explicite de la recharge brute par rapport à la recharge nette, et de l’ET des eaux souterraines vs. ET de la zone insaturée, dans la préparation des entrées du modèle et la présentation des résultats du modèle est nécessaire pour éviter une double comptabilisation dans le bilan hydrique. Les méthodes de modélisation de la recharge et d’ET comprennent (1) l’utilisation de conditions aux limites de surface simples pour les modèles d’écoulement des eaux souterraines, (2) le couplage de modèles en milieu aquifère saturé avec des modèles de la zone non saturé à une dimension, et (3) des conceptualisations plus complexes du couplage surface-zone non saturée et zone saturée. La modélisation numérique fournit des moyens pour intégrer des comportements de modèles complexes avec un effort de calcul réduit. Des données d’entrée précise de l’ET de surface sont essentielles pour obtenir des résultats précis des modèlesu2009; de plus, la conceptualisation du modèle dépend des échelles spatio-temporelles de la zone d’étude. En utilisant des données issues de la télédétection pour les données d’entrée concernant la recharge et l’ET dans l’étalonnage du modèle ou dans la fusion des données des modèles est un domaine pour le développement à venir de la recherche. Une amélioration de l’utilisation de l’analyse d’incertitude pour fournir les bornes de probabilité des données de sortie des modèles hydrogéologiques, une compréhension de la sensibilité du modèle et de la dépendance des paramètres, et des orientations pour des acquisitions complémentaires sur le terrain sont également des domaines pour la recherche future.ResumenSe proporciona una revisión de los métodos actuales y emergentes para el modelado de recarga y evapotranspiración (ET) a escala de cuenca en los sistemas de agua subterránea somera. Con el aumento de la disponibilidad de datos, tales como datos de temperatura en la superficie terrestre y la reflectancia de sensores remotos, ahora es posible modelar la recarga del agua subterránea y la ET con una complejidad físicamente más realista y con mayores niveles de confianza. La representación conceptual de recarga y de la ET en modelos de agua subterránea es crítica en zonas con el agua subterránea poco profunda. La dependencia de la profundidad de la recarga y la retroalimentación del uso del agua por la vegetación requiere una calibración adicional de los flujos, así como de las cargas hidráulicas. La definición explícita de la recarga bruta frente a la recarga neta, y la ET del agua subterránea frente a la ET de la zona no saturada, en la preparación de los datos de entrada del modelo y de información de los resultados del modelo es necesario para evitar la doble contabilización en el balance hídrico. Los métodos para el modelado de la recarga y de la ET incluyen (1) el uso de condiciones de contorno de superficie simples para los modelos de flujo de agua subterránea, (2) el acoplamiento de modelos de agua subterránea saturada con modelos unidimensionales de la zona no saturada, y (3) más complejas conceptualizaciones del acoplado saturada, no saturada y superficial. La emulación del modelo proporciona medios para la inclusión de modelos de comportamiento complejos con menor esfuerzo computacional. Una entrada precisa de la ET de superficie es esencial para salidas precisas de los modelos, y la conceptualización del modelo depende de las escalas espaciales y temporales bajo investigación. La utilización de información de sensores remotos para las entradas de la recarga y la ET en la calibración del modelo o en la fusión de datos del modelo es un área para el futuro desarrollo de la investigación. Una mejor utilización de los análisis de incertidumbre para proporcionar límites de probabilidad en los resultados de los modelos de las aguas subterráneas, la comprensión de la sensibilidad del modelo y la dependencia de parámetros y directrices para la posterior adquisición de datos de campo son también áreas de investigación futura.摘要论文对现有及新兴的流域范围浅层地下水的补给及蒸散量的建模方法进行了综述。随着可利用数据,如遥感反射率及地表温度数据的不断增多,现在对地表水的补给及蒸散量的建模可以实现更复杂的物理过程及更高级别的置信度。补给的深度关联和植被水分利用反馈需要额外校准流量及水头。总补给相对于净补给,地下水蒸散量相对于非饱和区蒸散量,这些概念的明确定义在准备模型输入和报告模型结果时候是必需的,以避免水平衡重复计算。地下水的补给及蒸散量的建模方法包括(1)使用简单的表面边界条件的地下水流模型,(2)耦合饱和地下水模型与一维不饱和区的模型,以及(3)更复杂的全耦合的“表面—不饱和—饱和”的概念化。元模型技术提供了一种以更低计算工作量来包含复杂的模型行为的方法。精确的蒸散量表面输入对于模型准确输出是必不可少的,模型的概念化依赖于研究的空间和时间尺度。在模型校准或模型数据融合时候使用补给和蒸散量的遥感信息作为输入是今后研究发展的一个领域。更好地利用不确定性分析,为地下水模型输出提供了可能性边界,了解模型的灵敏度和参数的依赖,并指导进一步的实地数据采集,也是今后研究的领域。ResumoUma revisão é fornecida dos métodos atuais e emergentes para a modelagem da recarga e evapotranspiração (ET) em sistemas aquíferos rasos em escala de bacia. Com o crescimento da disponibilidade de dados, assim como reflectância detectadas remotamente e dados de temperatura de superfície, agora, é possível a modelagem de recarga de águas subterrâneas e evapotranspiração com maior complexidade física e maiores níveis de confiança. A representação conceitual da recarga e ET nos modelos de águas subterrâneas é crítica em áreas de aquíferos rasos. A resposta da dependência da profundidade pela recarga e o uso da água pela vegetação requer calibração adicional para os fluxos assim como para as cargas. Definições explicitas de recarga bruta vs. recarga liquida, e ET em zona saturada vs. ET em zona não saturada, na definição dos dados de entrada do modelo e para relatar os resultados do modelo são necessárias para evitar computação dupla dos dados no balanço hídrico. Métodos para modelagem de recarga e evapotranspiração incluem (1) utilização de condições simples de contorno da superfície para modelos de fluxo de água subterrânea, (2) modelos de águas subterrâneas acoplados a modelos unidimensional de zona não saturada, e (3) conceptualizações mais complexas de acoplamentos completos entre a superfície, zona saturada e não-saturada. Emulação dos modelos fornece um meio de incluir comportamentos de modelos complexos com menor esforço computacional. Um dado de entrada de ET superficial preciso é essencial para a acurácia dos dados de saída do modelo, e a conceptualização do modelo depende nas escalas espaciais e temporais sob investigação. A utilização de informação de sensoriamento remoto para os dados de entrada de recarga e ET na calibração do modelo ou na fusão de dados ao modelo é uma área para futuro desenvolvimento de pesquisa. A utilização melhorada da análise de incerteza para fornecer margens probabilísticas para dos dados de saída do modelo de águas subterrâneas, entendendo a sensibilidade do modelo e a dependência de parâmetros, e orientação para maior aquisição de dados a campo são também área para futuras pesquisas.