Physically based modeling in catchment hydrology at 50: Survey and outlook

Integrated, process-based numerical models in hydrology are rapidly evolving, spurred by novel theories in mathematical physics, advances in computational methods, insights from laboratory and field experiments, and the need to better understand and predict the potential impacts of population, land use, and climate change on our water resources. At the catchment scale, these simulation models are commonly based on conservation principles for surface and subsurface water flow and solute transport (e.g., the Richards, shallow water, and advection-dispersion equations), and they require robust numerical techniques for their resolution. Traditional (and still open) challenges in developing reliable and efficient models are associated with heterogeneity and variability in parameters and state variables; nonlinearities and scale effects in process dynamics; and complex or poorly known boundary conditions and initial system states. As catchment modeling enters a highly interdisciplinary era, new challenges arise from the need to maintain physical and numerical consistency in the description of multiple processes that interact over a range of scales and across different compartments of an overall system. This paper first gives an historical overview (past 50 years) of some of the key developments in physically based hydrological modeling, emphasizing how the interplay between theory, experiments, and modeling has contributed to advancing the state of the art. The second part of the paper examines some outstanding problems in integrated catchment modeling from the perspective of recent developments in mathematical and computational science

Final Report of the DAUFIN project

DAUFIN = Data Assimulation within Unifying Framework for Improved river basiN modeling (EC 5th framework Project

Investigation of the factors controlling hyporheic exchangeat multiple spatial scales

Hyporheic exchange is the mixing between stream water and sediment pore water occurring vertically through the riverbed and laterally through the riverbanks. This mixing between water coming from the river and water coming from the aquifer, with very different physical and chemical characteristics, creates a unique environment in which important biogeochemical reactions occur and rich communities of microorganisms and macroinvertebrates flourish. The occurrence of the hyporheic exchange significantly influences the quality of the stream water and the nutrient cycling, playing a crucial role in hydrological, biogeochemical, and ecological processes. Although hyporheic fluxes are driven by the local morphology of the streambed, they are strongly affected by the large-scale groundwater system, which obstructs the penetration of stream water into the sediments and limits the intensity of hyporheic exchange. The present thesis aims to: i) investigate the role of the regional groundwater flow system on hyporheic exchange, analyzing the factors controlling the spatial variability of groundwater discharge patterns along the river corridor and ii) study the effect of microbial growth on exchange fluxes and nutrient reactions within the hyporheic sediments. The work is divided into five Chapters. Chapter 1 presents a general overview on groundwater-surface water interactions, with a description of the multiple scales involved in these processes. The main aspects for which these interactions are important are recalled and a brief review on the modeling,of river-aquifer interactions is presented. The attention is then focused on hyporheic processes, analyzing the main hydraulic and biogeochemical features characterizing these processes. The impact that the groundwater flow system has on these local processes is discussed. Finally, the main research topics investigated in the thesis are outlined. In Chapter 2, the role of groundwater table structure at basin scale on the spatial patterns of groundwater discharge to the stream network and, consequently, on hyporheic exchange was investigated. Specifically, we determined the spatial structure of the groundwater upwelling along the stream network in order to investigate the effect of large-scale groundwater flow on local hyporheic flow velocity. A semi-analytical method for the estimation of the three-dimensional groundwater flow field was adopted, based on an approximation between the groundwater head distribution and the landscape topography. Results highlight that the complex topographic conformation of a basin determines a strong spatial variability of the groundwater flow field that, in turn, translates into a fragmentation of the hyporheic zone. Chapter 3 is in line with the study developed in Chapter 2, looking at the groundwater-surface water interactions induced by large-scale hydrogeological characteristics. A more complex numerical model was adopted, allowing us to remove some simplifications on which the previous semi-analytical model was based on. The influence of some topographic and hydrogeological factors on determining the spatial variability of groundwater discharge patterns was investigated. Results indicate that the geological heterogeneity of the aquifer is the main control of river-aquifer exchange patterns and the structure of subsurface flow patterns is marginally affected by other modeling assumptions. Chapter 4 shifts the focus on biogeochemical processes occurring at smaller scales and deals with the existing coupling between hydrodynamic processes, solute transport, and microbial metabolism within the hyporheic zone. A flow and reactive transport model was coupled with a microbial biomass model where two microbial components representing autotrophic (nitrifying) bacteria and heterotrophic (facultative anaerobic) bacteria were considered. The aim was to investigate how the filling of sediment pore space induced by biomass growth (i.e. bioclogging) alters hyporheic flow patterns and transformation rates of nitrogen, oxygen, and organic carbon within hyporheic sediments. Results show how the bioclogging-induced biogeochemical zonation of hyporheic zone strongly influences coupled nitrogen, carbon, and oxygen dynamics. Finally, Chapter 5 presents general conclusions of the work

Hyperresolution information and hyperresolution ignorance in modelling the hydrology of the land surface

There is a strong drive towards hyperresolution earth system models in order to resolve finer scales of motion in the atmosphere. The problem of obtaining more realistic representation of terrestrial fluxes of heat and water, however, is not just a problem of moving to hyperresolution grid scales. It is much more a question of a lack of knowledge about the parameterisation of processes at whatever grid scale is being used for a wider modelling problem. Hyperresolution grid scales cannot alone solve the problem of this hyperresolution ignorance. This paper discusses these issues in more detail with specific reference to land surface parameterisations and flood inundation models. The importance of making local hyperresolution model predictions available for evaluation by local stakeholders is stressed. It is expected that this will be a major driving force for improving model performance in the future. Keith BEVEN, Hannah CLOKE, Florian PAPPENBERGER, Rob LAMB, Neil HUNTE

Modeling water resources management at the basin level: review and future directions

Water quality / Water resources development / Agricultural production / River basin development / Mathematical models / Simulation models / Water allocation / Policy / Economic aspects / Hydrology / Reservoir operation / Groundwater management / Drainage / Conjunctive use / Surface water / GIS / Decision support systems / Optimization methods / Water supply

FLOWPATH 2019 – NATIONAL MEETING ON HYDROGEOLOGY

FLOWPATH 2019, the 4th National Meeting on Hydrogeology, was held in Milan from 12th to 14th June 2019. According to the aim of the previous Editions of FLOWPATH, held in Bologna (2012), Viterbo (2014) and Cagliari (2017), the conference is an opportunity for Italian hydrogeologists to exchange ideas and knowledge on different groundwater issues. The objectives of the conference are: – To promote dialogue and exchange of scientific knowledge among young hydrogeologists; – To deepen the theoretical and practical aspects of our understanding on groundwater; – To update all the stakeholders, researchers and professionals on recent challenges in the hydrogeological sciences; – To encourage researchers, professionals and administrators to contribute to the improvement of water resources management

Integrating coupled simulation of surface water and groundwater with Artificial Intelligence

Surface water and groundwater, integral to the hydrological cycle, engage in complex hydraulic interactions and frequent transformations. Isolating surface water and groundwater systems in individual studies often fails to capture and analyse their interrelationships, limiting the comprehensive understanding of regional water resources. Additionally, conventional physics-based coupled models encounter challenges arising from the complexities and non-linearity of interactions, impeding their accuracy in simulation results. To address this challenge, this thesis proposes a novel framework that integrates artificial intelligence and physics-based coupled models to simulate variations in surface water and groundwater, establishing a foundation for integrated water resource management. Specifically, the study develops a boundary-coupled framework to model interactions between surface water and groundwater. In this framework, a data-driven deep learning model is employed to simulate surface water flow. Additionally, physics-based analytical models are used to describe groundwater movement in riparian zones, while simplifying river behaviour to a Dirichlet boundary condition to assimilate data from the surface water model. Subsequently, the simulated values from analytical solutions serve as the source data, while groundwater observation data is employed as the target data. A transfer learning model is then be utilized to learn the features of the source data and, in conjunction with the target dataset, facilitate the prediction and regression of groundwater. Finally, the framework is applied at the watershed scale to predict and model catchment-scale surface water flow and groundwater head. In this framework, the thesis assesses the influence of various input variables on surface water prediction, explores the effect of groundwater layer heterogeneity, and validates the effectiveness of the deep transfer learning approach, particularly in catchment-scale predictions. The main conclusions are as follows: 1. The selection of model inputs greatly influences accuracy. The PCA method effectively enhances the precision of the deep RNN model, especially in scenarios with numerous input variables. It achieves this by distilling essential information, categorizing original data into several comprehensive variables. 2. The two-layer structure significantly influences groundwater flow responses to hydrological events. During recharge events with a less permeable upper layer, lateral discharge to the river is hindered, directing more groundwater downward into the more permeable lower layer. Conversely, when the upper layer is more permeable, greater lateral flow into the river occurs, with less downward flow into the less permeable lower layer. During a flood event with a less permeable upper layer, river water predominantly infiltrates the more permeable lower layer initially, then flows upward into the upper layer, creating a vertical flow. The direction of this flow reverses during the recession period. However, this phenomenon is not evident when the upper layer is more permeable than the lower layer. 3. The transfer learning method can enhance the capacity of analytical solutions for heterogeneous aquifers. By integrating analytical knowledge with the neural network, the analytical solution-transfer learning method significantly improves hydraulic head prediction accuracy. Even for very sparse training data, the analytical solution-transfer learning method still performs more satisfactorily than the traditional deep learning method. 4. The analytical solution-transfer learning method is also effective at the catchment scale. The analytical solution-transfer learning method can obtain more accuracy and robust results than traditional deep learning methods with the same training dataset

Regional groundwater flow dynamics and residence times in Chaudière-Appalaches, Québec, Canada : insights from numerical simulations

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2017-2018Dans le cadre du projet PACES III pour la région de Chaudière-Appalaches, situé au sud de la ville de Québec, au Canada, l'étude présente une analyse approfondie de l’influence des dynamiques d’écoulement sur la qualité des eaux souterraines dans un contexte régional. L’écoulement régional, le transport d’âge et l'impact d'une faille sur la qualité de l'eau souterraine sont étudiés par l’entremise de modèles numériques bidimensionels. La combinaison des connaissances hydrogéologiques physiques et chimiques, y compris une analyse des concentrations de ¹⁴C dans les eaux souterraines échantillonnées, a conduit à l’ébauche d'un modèle conceptuel de l’écoulement régional. Ce dernier est mis à l’essais pas l’entremise d’un modèle d'écoulement numérique suivant une ligne d’écoulement régionale dans le plan 2D vertical à l’aide du logiciel FLONET. Le modèle est d'abord calibré à l’aide d’une méthode semi-automatisé qui utilise le logiciel PEST en comparant les charges simulés à la piézométrie régionale, et est validé par la comparaison des flux simulés à la recharge. Bien que le modèle affiche l’existence d’un écoulement régional profond, la région à l’étude apparaît être dominée par des systèmes d'écoulements locaux à des échelles maximales d'environ 5 km, avec un écoulement significatif dans le roc fracturé peu profond. L’écoulement actif se limitant à une profondeur maximale de 40 m à 60 m du roc fracturé, confirme que la géochimie des eaux souterraines échantillonnées à partir de puits résidentiels est susceptible d'être affectée par les eaux faisant parti de l’écoulement intermédiaire et régional. Le transport advectif-dispersif de l'âge est ensuite simulé avec le simulateur de transport TR2 et comparé aux temps de déplacement advectifs le long des lignes d’écoulements et à l'âge ¹⁴C des eaux échantillonnées. Enfin, l’influence de la faille de la Rivière Jacques Cartier sur le contexte hydrogéologique régional est étudiée à travers divers scénarios hypothétiques de perméabilité de faille.As part of the PACES III project in the Chaudière-Appalaches region, south of Quebec City, Quebec, Canada, the study herein presents insights into the extent to which regional groundwater quality is shaped by flow dynamics. In this context, 2D numerical modelling is used to simulate regional flow, transport of groundwater age and the possible influence of a fault on groundwater quality. Combining physical and chemical hydrogeological knowledge, including an analysis of ¹⁴C concentrations in sampled groundwater, leads to the development of a regional conceptual flow model. The conceptual model is tested by representing the system with a two-dimensional numerical flow model oriented in the vertical plane roughly south-north towards the St. Lawrence River using the FLONET code. The model is first calibrated to regional piezometry through a semi-automated workflow using PEST and is then validated with average recharge values. Although some evidence for deeper regional flow exists, the area appears to be dominated by local flow systems on maximum length scales of about 5 km, with significant flow through the shallow fractured sedimentary rock aquifer. This regional scale flow model is also supported by the local hydrogeochemical signatures. Active flow appears contained within the top 40 m to 60 m of the fractured bedrock, which confirms that the geochemical signatures of groundwater sampled from residential wells are likely affected by the slow moving waters of the intermediate and regional flow systems. Advective-dispersive transport of groundwater age is then simulated with the TR2 transport model and compared with advective travel times and sampled ¹⁴C water ages. Finally, the possible role of the Jacques-Cartier River fault on regional flow dynamics is investigated by testing various fault permeability configurations