Optimal operation of water reclamation facilities (WRFs) is critical for an indirect potable reuse (IPR) system, especially when the reclaimed water constitutes a major portion of the reservoir's safe yield. It requires timely and informed decision-making in response to the fluctuating operational conditions, e.g., weather patterns, plant performance, water demand, etc. Advanced integrated modeling techniques can be used to develop reliable operational strategies to mitigate future risks associated with water quality without needing high levels of financial investment. The Upper Occoquan Service Authority (UOSA) WRF, located in northern Virginia, discharges nitrified reclaimed water directly into a tributary of the Occoquan Reservoir, one of the major water supply sources for Fairfax County. Among the many operational challenges at UOSA, one is to regulate the nitrate concentration in its reclaimed water based on the denitrifying capacity of the reservoir. This study presents an integrated model that is used to predict future reservoir conditions based on the weather and streamflow forecasts obtained from the Climate Forecast System and the National Water Model. The application captures the dynamic transformations of the pollutant loadings in the streams, withdrawals by the water treatment plant, WRF effluent flows, and plant operations to manage the WRF performance. It provides plant operators with useful feedback for correctly targeting the effluent nitrates using an intelligent process simulator called IViewOps. The platform is powered by URUNME, a new software that fully automates the operation of the reservoir and process models integrating forecasting products, and data sources. URUNME was developed in C#.NET to provide out-of-the-box functionality for model coupling, data storage, analysis, visualization, scenario management, and decision support systems. The software automatically runs the entire integrated model and outputs data on user-friendly dashboards, displaying historical and forecasting trends, on a periodic basis. This decision support system can provide stakeholders with a holistic view for the design, planning, risk assessments, and potential improvements in various components of the water supply chain, not just for the Occoquan but for any reservoir augmentation type IPR system. / Doctor of Philosophy / In an indirect potable reuse (IPR) system, reclaimed water from an advanced wastewater treatment facility is blended with a natural water source, such as a reservoir, to augment drinking water supply. Reliable operation of such a system is critical, especially when the reclaimed water constitutes a major portion of the withdrawals from the reservoir for treatment and distribution. One example of such an IPR system is the Upper Occoquan Service Authority (UOSA) water reclamation facility (WRF) which discharges its reclaimed water into the Occoquan Reservoir, a key water resource for Fairfax County. Integrated environmental modeling (IEM) provides a comprehensive approach towards the design and operation of water resource systems in which water supply, drainage, and sanitation are simulated as a single entity rather than independent units. In IEM, different standalone models, each representing a single subsystem, are linked together to analyze the complex interactions between various components of the system. This approach can be used for developing operational support tools for an IPR system to ensure timely and informed decision-making in response to the fluctuating conditions, e.g., weather patterns, plant performance, water demand, etc. The overarching goal of this research was to integrate different models and the data sources and develop a decision support system (DSS) to manage the UOSA-WRF performance. This resulting integrated model is used to predict future reservoir conditions based on the weather and streamflow forecasts obtained from the National Weather Service. The application runs various future scenarios to capture the possible variations of the pollutant loadings in the streams, withdrawals by the water treatment plant, WRF effluent flows, and plant operations and provide feedback to plant operators. The entire integrated model is operated periodically to output data on user-friendly dashboards, displaying historical and forecasting trends. The DSS provides stakeholders with a holistic view for the design, planning, risk assessments, and potential improvements in various components of the water supply chain, not just for the Occoquan but for any reservoir augmentation type IPR system.

La région Méditerranéenne a été identifiée comme l'une des régions les plus vulnérables aux changements climatiques et anthropiques et constitue un des « hot-spots » mondiaux de crise de l'eau. Dans un tel contexte, les questions relatives à la gestion des ressources en eau se posent de manière accrue. Pour y faire face, des approches de modélisation intégrée associant l'évaluation de la disponibilité des ressources en eau et des demandes en eau sont proposées. Une chaîne méthodologique a été mise en place à l'échelle régionale, considérant des scénarios hydrologiques et d'usages de l'eau sous contraintes climatiques et incluant les objectifs de la Stratégie Méditerranéenne pour le Développement Durable en termes d'efficience hydraulique. Cette première approche permet d'évaluer la situation du stress hydrique en Méditerranée et son évolution à l'horizon 2050. Actuellement, le Sud et l'Est de la Méditerranée doivent faire face à un stress hydrique sévère, voire à une pénurie. D'ici 2050, les ressources en eau disponibles pourraient diminuer de l'ordre de 30 à 50 % tandis que les prélèvements devraient doubler. Le stress hydrique devrait ainsi augmenter sur l'ensemble du pourtour méditerranéen. Néanmoins, si les objectifs d'efficience sont atteints, les prélèvements en eau pourraient se stabiliser, voire même diminuer (10–40 %) dans certains bassins Nord méditerranéens. Le stress hydrique pourrait alors rester faible sur la rive Nord et être tempéré dans certains bassins de la rive Est. Une deuxième chaîne méthodologique a été développée à l'échelle du bassin de l'Ebre (Espagne) afin d'appréhender la satisfaction des demandes en eau environnementales, domestiques et agricoles. Le bassin a été divisé en 9 sous-bassins versants afin de considérer les différentes contraintes hydro-climatiques et l'influence des barrages principaux sur les régimes hydrologiques, auxquels ont été associés 11 sites de demande. Cette approche permet de définir les pressions actuelles sur le bassin et d'évaluer l'évolution de la capacité à satisfaire les demandes en eau sous contrainte de scénarios climatique, d'évolution démographique et d'expansion des surfaces irriguées à moyen terme. Actuellement, les demandes en eau sur le bassin versant de l'Ebre sont satisfaites. A l'horizon 2050, les écoulements printaniers et estivaux pourraient diminuer de 30 à 35 % en différents points du bassin. Les demandes en eau environnementales et domestiques devraient toujours être satisfaites, néanmoins, la capacité à satisfaire les besoins agricoles pourrait ne pas toujours être assurée au cours de la période estivale. Ces deux démarches établissent une confrontation entre l'offre et la demande en eau à différentes échelles et fournissent des indicateurs sur la capacité à satisfaire les demandes en eau sous contraintes climatiques et anthropiques. Elles constituent ainsi des approches originales pour évaluer la disponibilité actuelle et future des ressources en eau, identifier les régions où des tensions d'usages risquent de se produire et mieux orienter les stratégies d'adaptation. Dans un contexte de changements globaux, ce type d'exercice est fondamental pour soutenir les politiques de gestion de l'eau et encourage la co-construction de scénarios entre usagers, décisionnaires et scientifiques. / The Mediterranean basin has been identified as one of the world's most vulnerable regions to climatic and anthropogenic changes and constitutes a water crisis' hot spot. Under such context, questions on water resources management arise. Integrated methodologies taking into account evolution in water resources availability and water demands are thus generated. A first methodology accounting for the Mediterranean basin specific conditions is developed to assess the current and future water stress state of this region. The medium-term evolution of water stress is investigated using climatic scenarios and a water-use scenario based on efficiency improvements following the recommendations of the Mediterranean Strategy for Sustainable Development. Currently, the southern and eastern rims are experiencing high to severe water stress. By the 2050 horizon, a 30–50% decline in freshwater resources is simulated over most of the Mediterranean basin and total water withdrawals are projected to double. Water stress could hence increase over the whole Mediterranean basin. If progresses in efficiency are reached, total water withdrawals would stabilize over the Mediterranean basin and even make them decrease (10–40%) in many northern catchments. Water stress could thus be tempered in some eastern catchments and kept to low on the northern rim. A second integrated water resources modelling framework was developed over the Ebro catchment (Spain) in order to evaluate water allocation for the domestic and agricultural sector as well as for environmental purposes. The catchment was divided into 9 sub-catchments to which 11 demand sites were attributed, in order to take into account the different hydro-climatic regimes and the influence of dams on hydrological regimes. This method defines current pressures applied to water resources and evaluates the evolution of water allocation by the medium term under climatic and water-use scenarios considering population growth and irrigated areas expansion. Currently, water demands are satisfied over the Ebro catchment. In 2050, water resources are projected to decline by 30-35% during the spring and summer seasons. Environmental and domestic water demands should still be satisfied but agricultural water demands could have to face severe water shortages during the summer season. These two modeling frameworks establish a dialogue between water resources and water demands at different space scales and give indexes on the capacity to satisfy water demands under climatic and anthropogenic scenarios. These studies provide original approaches to evaluate water resources current and future availability, to identify the most vulnerable regions to water use conflicts and to better orientate adaptation strategies. In a context of climatic and anthropogenic changes, such frameworks are a first step to better sustain water management policies and to support the co-construction of scenarios between users, policy-makers and scientists.

The main objective of this study is to develop a modeling methodology that facilitates incorporating the plant pathway into environmental contamination models recognizing the fact that plants are dynamic entities that regulate their life cycle according to natural and anthropogenic environmental conditions. A modeling framework that incorporates the plant pathway into an integrated water flow and contaminant transport model in terrestrial systems is developed. The modeling framework is aimed to provide a tool to analyze the plant pathway of exposure to contaminants. The model developed using this framework describes the temporal and spatial variation of the contaminant concentration within the plant as it is interacting with the soil and the atmosphere. The first part of the study focuses on the integration of the dynamics of water and contaminant distribution and plant related processes within the vadose zone. A soil-plant system model is developed by coupling soil-water flow, contaminant transport, plant life-cycle, and plant pathway models. The outcome unifies single media continuous models with multimedia compartmental models in a flexible framework. The coupling of the models was established at multiple interfaces and at different levels of solution steps (i.e. model development phase vs. numerical solution phase). In the second part of the study, the soil-plant system model is extended to cover large spatial areas by describing the environmental system as a collection of soil-plant systems connected through overland flow and transport processes on the ground surface and through lateral interactions in the subsurface. An overland flow model is integrated with the previously coupled model of unsaturated zone soil-water flow and plant life-cycle by solving the flow model equations simultaneously within a single global matrix structure. An overland / subsurface interaction algorithm is developed to handle the ground surface conditions. The simultaneous solution, single-matrix approach is also adopted when integrating the overland transport model with the previously coupled models of vadose zone transport and plant pathway. The model developed is applied to various environmental contamination scenarios where the effect of the presence of plants on the contaminant migration within environmental systems is investigated.

<div>With increasing focus on large scale planning and allocation of resources for protection against future flood risk, it is necessary to analyze and improve the deficiencies in the conventional flood modeling approach through a better understanding of the interactions between river hydrodynamics and subsurface processes. Recent studies have shown that it is possible to improve the flood inundation modeling and mapping using physically-based integrated models that incorporate observable data through assimilation and simulate hydrologic fluxes using the fundamental laws of conservation of mass at multiple spatiotemporal scales. However, despite the significance of integrated modeling in hydrology, it has received relatively less attention within the context of flood hazard. The overall aim of this dissertation is to study the heterogeneity in complex physical processes that govern the watershed response during flooding and incorporate these effects in integrated models across large scales for improved flood risk estimation. Specifically, this dissertation addresses the following questions: (1) Can physical process incorporation using integrated models improve the characterization of antecedent conditions and increase the accuracy of the watershed response to flood events? (2) What factors need to be considered for characterizing scale-dependent physical processes in integrated models across large watersheds? (3) How can the computational efficiency and process representation be improved for modeling flood events at large scales? (4) Can the applicability of integrated models be improved for capturing the hydrodynamics of unprecedented flood events in complex urban systems?</div><div><br></div><div>To understand the combined effect of surface-subsurface hydrology and hydrodynamics on streamflow generation and subsequent inundation during floods, the first objective incorporates an integrated surface water-groundwater (SW-GW) modeling approach for simulating flood conditions. The results suggest that an integrated model provides a more realistic simulation of flood hydrodynamics for different antecedent soil conditions. Overall, the findings suggest that the current practice of simulating floods which assumes an impervious surface may not be providing realistic estimates of flood inundation, and that an integrated approach incorporating all the hydrologic and hydraulic processes in the river system must be adopted.</div><div><br></div><div>The second objective focuses on providing solutions to better characterize scale-dependent processes in integrated models by comparing two model structures across two spatial scales and analyzing the changes in flood responses. The results indicate that since the characteristic length scales of GW processes are larger than SW processes, the intrinsic scale (or resolution) of GW in integrated models should be coarser when compared to SW. The results also highlight the degradation of streamflow prediction using a single channel roughness when the stream length scales are increased. A distributed channel roughness variable along the stream length improves the modeled basin response. Further, the results highlight the ability of a dimensionless parameter 𝜂1, representing the ratio of the reach length in the study region to maximum length of the single stream draining at that point, for identifying which streams may require a distributed channel roughness.</div><div><br></div><div>The third objective presents a hybrid flood modeling approach that incorporates the advantages of both loosely-coupled (‘downward’) and integrated (‘upward’) modeling approaches by coupling empirically-based and physically-based approaches within a watershed. The computational efficiency and accuracy of the proposed hybrid modeling approach is tested across three watersheds in Indiana using multiple flood events and comparing the results with fully- integrated models. Overall, the hybrid modeling approach results in a performance comparable to a fully-integrated approach but at a much higher computational efficiency, while at the same time, providing objective-oriented flexibility to the modeler.</div><div><br></div><div>The fourth objective presents a physically-based but computationally-efficient approach for modeling unprecedented flood events at large scales in complex urban systems. The application of the proposed approach results in accurate simulation of large scale flood hydrodynamics which is shown using Hurricane Harvey as the test case. The results also suggest that the ability to control the mesh development using the proposed flexible model structure for incorporating important physical and hydraulic features is as important as integration of distributed hydrology and hydrodynamics.</div>

Dans les territoires irrigués exposés aux crises de gestion quantitative de l’eau, la sévérité des étiages dépend des interactions entre systèmes de culture, situations pédoclimatiques, hydrologie, lâchers d’eau et restriction d’irrigation. Dans de nombreuses situations, l’absence de nouvelles solutions de stockage et les tensions entre gestionnaires et usagers de l’eau rendent nécessaire la planification des étiages. Mes travaux explorent le potentiel de « la gestion spatiale » de l’eau pour mettre en adéquation la dynamique des prélèvements pour l’irrigation avec celle de l’offre en eau disponible (naturelle et stockée). Je propose une méthodologie participative de conception-évaluation d’organisations territoriales des activités agricoles, déployée sur l’aval du bassin versant de l’Aveyron (800 km²), en trois étapes: (1) modéliser le système socio-agro-hydrologique, (2) concevoir des alternatives de distribution spatiale des systèmes de culture, (3) conduire une évaluation intégrée des alternatives face à la variabilité climatique observée. Ces travaux combinent des méthodes, connaissances et outils « hard and soft », et font usage de la plateforme de simulation multi-agent MAELIA. Le processus a permis de formaliser des visions d’acteurs et de poser les bases d’une concertation multi acteur. Cependant la simulation des impacts de ces alternatives a montré leurs limites pour régler le problème de déficit structurel en eau. Cette démarche pourrait être prolongée pour aboutir à des propositions opérationnelles. / In irrigated landscapes exposed to quantitative water management crisis, the intensity of low flows depends on interactions between cropping systems, pedoclimatic situation hydrology, water releases and withdrawal restrictions. In many situations there are no opportunities for more water storage, thus tensions occur between water managers and users, which makes the planning of water demand dynamics necessary. My work explores the potentials in the “spatial management of water” to align the water demand dynamics with natural and stored water availability. I present a 3 step, participatory method to design and assess agricultural landscapes: (1) model the Social-Agro Hydrological system, (2) design alternative spatial distribution of the cropping systems, (3) carry an integrated assessment of those alternatives based on observed climatic variability. This method combines “hard” and “soft” methods, knowledge and tools, and uses the MAELIA multi-agent simulation platform. I tested the method tested in the downstream area of the Aveyron River (800 km² Southwestern France). It allowed to formalize the actors’ visions on alternative distributions of the cropping systems. However they showed to be limited in solving the water deficit issue. The method could be continued to reach operational proposals.