The Analysis of Seasonally Varying Flow in a Crystalline Rock Watershed Using an Integrated Surface Water and Groundwater Model

Researchers, explorers, and philosophers have dedicated many lifetimes attempting to discover, document, and quantify the vast physical processes and interactions occurring in nature. Our understanding of physical processes has often been reflected in the form of numerical models that assist academics in unraveling the many complexities that exist in our physical environment. To that end, integrated surface water-groundwater models attempt to simulate the complex processes and relationships occurring throughout the hydrologic cycle, accounting for evapotranspiration and surface water, variably saturated groundwater, and channel flows. The Bass Lake watershed is located in the Muskoka district of Ontario, within a crystalline rock environment consistent with typical Canadian Shield settings. Numerous data collection programs and methods were used to compile environmental and field-scale datasets. The integrated surface water-groundwater model, HydroGeoSphere (Therrien et al. , 2005), was used for all Bass Lake watershed simulation models. Simulation results were compared to expected trends and observed field data. The groundwater heads and flow vector fields show groundwater movement in expected directions with reasonable flow velocities. The subsurface saturation levels behave as expected, confirming the evapotranspiration component is withdrawing groundwater during plant transpiration. The surface water depths and locations of water accumulation are consistent with known and collected field data. The surface waters flow in expected directions at reasonable flow speeds. Simulated Bass Lake surface elevations were compared to observed surface water elevations. Low overland friction values produced the most accurate Bass Lake elevations, with high overland friction values slightly overestimating the Bass Lake water level throughout the simulation period. Fluid exchange between surface water and groundwater domains was consistent with expected flux rates. The integrated surface water-groundwater model HydroGeoSphere ultimately produced acceptable simulations of the Bass Lake model domain

The capacity of the Cape Flats aquifer and its role in water sensitive urban design in Cape Town

There is growing concern that South Africa's urban centres are becoming increasingly vulnerable to water scarcity due to stressed surface water resources, rapid urbanisation, climate change and increasing demand for water. Furthermore, South Africa is a water-stressed country with much of its surface water resources already allocated to meet current demands. Therefore, in order to meet the future urban water supply requirements, countries like South Africa will need to consider alternative forms of water management that focus on moving towards sustainability in urban water management. WSUD is one such approach that aims to prioritise the value of all urban water resources through reuse and conservation strategies, and the diversification of supply sources. This study investigates the capacity of the Cape Flats Aquifer (CFA), assessing the feasibility of implementing Managed Aquifer Recharge (MAR) as a strategy for flood prevention and supplementing urban water supply. The implementation of MAR on the CFA aims to facilitate the transition towards sustainable urban water management through the application Water Sensitive Urban Design (WSUD) principles. The fully-integrated MIKE SHE model was used to simulated the hydrological and hydrogeological processes of the CFA in Cape Town at a regional-scale. Using the results of the regional-scale model, four sites were selected for more detailed scenario modelling at a local-scale. Several MAR scenarios were simulated to evaluate the aquifer's response to artificial recharge and abstraction under MAR conditions. The first objective was to evaluate the feasibility of summer abstractions as a flood mitigation strategy at two sites on the Cape Flats prone to winter groundwater flooding, viz. Sweet Home and Graveyard Pond informal settlements. The second objective of the study was to assess the storage potential and feasibility of MAR at two sites in the south of the Cape Flats, at Philippi and Mitchells Plain. In addition, the migration of solute pollutants from the injected or infiltrated stormwater was simulated and climate change simulations were also undertaken to account for potential fluctuations in rainfall and temperature under climate change conditions. The results indicated that flood mitigation on the Cape Flats was possible and was likely to be most feasible at the Graveyard Pond site. The flood mitigation scenarios did indicate a potential risk to local groundwater dependent ecosystems, particularly at the Sweet Home site. Yet, it was shown that a reduction in local groundwater levels may have ecological benefits as many of the naturally occurring wetlands on the Cape Flats are seasonal, where distinct saturated and unsaturated conditions are required. Furthermore, MAR was shown to improve the yield of wellfields at Philippi and Mitchells Plain through the artificial recharge of stormwater while also reducing the risk of seawater intrusion. MAR was shown to provide a valuable means of increasing groundwater storage, improving the supply potential of the CFA for water supply while aiding the prevention or mitigation of the seasonal flooding that occurs on the Cape Flats. Furthermore, the case was made that MAR is an important strategy to assist the City of Cape Town in achieving its WSUD objectives. MAR and groundwater considerations, in general, are essential for the successful implementation of WSUD, without which, there is an increased risk of overlooking or degrading urban groundwater resources. The findings of this study resulted in a number of recommendation to urban water resources managers, planners and policy makers. First, MAR is an important means for Cape Town to move towards becoming a truly water sensitive city. This study indicated that the CFA should be incorporated as an additional source of water supply for Cape Town especially considering the recent drought conditions and due to its ability for the seasonal storage of water, this would improve the city's resilience to climate change. Furthermore, it was recommended that the application of MAR on the CFA could also be used to reduce groundwater related flooding on the Cape Flats. Second, it was emphasised that urban planning, using WSUD principles is essential for the protection of the resource potential of the CFA. Finally, for the implementation of WSUD and MAR to be successful, there needs to be appropriate policy development alongside the implementation of these strategies to ensure they are achieving their initial objectives and are not causing detriment to the aquifer

Simulating groundwater and surface water flow and solute transport in tile-drained landscapes

Dans des conditions de climat humide et lorsque les sols sont peu perméables, les systèmes de drainage souterrains sont généralement utilisés pour contrôler le niveau de la nappe phréatique et améliorer la production agricole. Cependant, les drains souterrains modifient à la fois les voies d'écoulement hydrologique et les taux de transport des nutriments des terres cultivées vers les eaux de surface, pouvant détériorer la qualité des eaux souterraines et de surface. De plus, des macropores sont souvent présents dans les sols composés de till argileux, ce qui génère un flux d'eau rapide et riche en nutriments de la surface du sol vers les drains souterrains. Une approche rentable pour réduire le lessivage des nutriments provenant de l'agriculture consiste à imposer des restrictions uniquement dans les zones vulnérables à la contamination de l'eau. Ces zones peuvent être identifiées à l'aide de modèles hydrologiques distribués. Les résultats obtenus sur de petits bassins versants expérimentaux doivent être simplifiés pour être appliqués à des échelles plus grandes, généralement requises pour l'élaboration de politiques. L'objectif de cette étude était d'examiner les avancées et les limitations de l'inclusion des drains souterrains dans les modèles d'écoulement de surface et souterrain. Les objectifs spécifiques étaient de i) démontrer l'utilisation des estimations de conductivité électrique spécifique (CE), pour améliorer les simulations hydrologiques dans un champ drainé, ii) étudier l'efficacité d'un modèle hydrologique et de transport de soluté tridimensionnel pour simuler un test de traçage de bromure (Br) dans un champ drainé et iii) évaluer différents modèles conceptuels de drains souterrains et d'hétérogénéité du sol pour la simulation numérique du drainage dans un bassin versant agricole au Danemark. Les résultats suggèrent que la simulation de la profondeur de la nappe phréatique peut être améliorée par l'inclusion d'hétérogénéités basées sur des estimations de la CE. L'approche des seepage nodes était appropriée pour simuler les débits de drainage, cependant la précision des simulations était meilleure pour les modèles à l'échelle du terrain. À l'échelle du bassin versant, le fait de ne représenter que les drains principaux est approprié pour pouvoir utiliser des maillages plus grossiers et pour simuler le débit des cours d'eau et les faibles profondeurs des eaux de surface dans les zones drainées. Des résultats similaires ont été obtenus lorsque les seepage nodes ont été appliqués sur l'ensemble des zones agricoles, sans tenir compte de l'emplacement spécifique des drains souterrains. Cette dernière approche peut être appliquée lorsque les drains souterrains ne sont pas cartographiés, ce qui est généralement le cas. Une représentation simplifiée de l'hétérogénéité et de la macroporosité peut expliquer les différences entre ls valeurs observées et simulées des charges hydrauliques, débits de drainage et processus de transport de solutés. Les approches de modélisation étudiées dans cette thèse peuvent améliorer la représentation de la dynamique de l'écoulement souterrain et les simulations du transport de substances agrochimiques lessivées des champs cultivés, telles que le nitrate et phosphate.Under humid climate conditions and for low-permeability soils, subsurface tile drains are usually employed to lower the water table and enhance agricultural production. However, tile drains alter both the hydrologic flow pathways in agricultural catchments and the rates of nutrient transport from cropland to surface water bodies, potentially impairing the groundwater and surface water quality. Furthermore, macropores are often present in clayey till soils, generating rapid and nutrient-rich water flow from the ground surface to the tile drains. A cost-effective approach to reduce nutrient leaching from agriculture is to impose restrictions only in vulnerable areas to water contamination, which can be identified using distributed hydrological models. Results on small experimental catchments need to be simplified for application on larger scales, usually required for policy-making purposes. The objective of this study was to investigate the outcomes and limitations of including tile drains in surface and subsurface flow models. Specific objectives were to i) demonstrate the use of electrical conductivity (EC) estimates to improve hydrological simulations in a tile-drained field, ii) investigate the efficiency of a three-dimensional hydrological and solute transport model to simulate a bromide (Br) tracer test in a tile-drained field and iii) assess different conceptual models for tile drains and soil heterogeneity for the numerical simulation of tile drainage in an agricultural catchment in Denmark. The results suggest that the simulation of the water table depth can be improved by the inclusion of heterogeneities based on EC estimates. The seepage nodes approach was suitable to simulate drain discharge, however the accuracy of the simulations was better for the field-scale models. At the catchment scale, representing only the main drains was suitable to reduce the mesh refinement and simulate stream flow and low surface water depths in drained areas. Similar results were obtained when seepage nodes were applied all over the agricultural areas, without considering the specific location of tile drains. The later approach can be applied when tile drains are not mapped, which is usually the case. The misrepresentation of heterogeneity and macroporosity may explain the differences between observed and simulated hydraulic heads, drain discharge and solute transport processes. The modeling approaches investigated in this dissertation can improve subsequent simulations of tile drainage and the transport and fate of leached agrochemicals such as nitrate or phosphate

Earth Systems Modeling in the Brazos River Alluvium Aquifer: Improvement of Computational Methods and Development of Conceptual Model

Traditional hydrologic modeling has compartmentalized the water cycle into distinct components (e.g. Traditional hydrologic modeling has compartmentalized the water cycle into distinct components (e.g. rainfall-runoff, river routing, or groundwater flow models). In river valley alluvium aquifers, these processes are too interconnected to be represented accurately by separate models. An integrated modeling framework assesses two or more of these components simultaneously, reducing the error associated with approximated boundary conditions. One integrated model, ParFlow.CLM, offers the advantage of parallel computing, but it lacks any mechanism for incorporating time-varying streamflow as an upstream boundary condition. Previous studies have been limited to headwater catchments. Here, a generalized method is developed for applying transient streamflow at an upstream boundary in ParFlow.CLM. The upstream inflow method was successfully tested on two domains – one idealized domain with a straight channel, and one small stream catchment in the Brazos River Basin. The stream in the second domain is gaged at the upstream and downstream boundaries. Both tests assumed a homogeneous subsurface, so that the efficacy of the transient streamflow method could be evaluated with minimal complications by groundwater interactions. Additionally, an integrated conceptual model is presented for the Brazos River Alluvium Aquifer (BRAA), the Brazos River, and the overlying terrain. The BRAA is a floodplain aquifer in central to southeast Texas. This aquifer is highly connected to the Brazos River and experiences localized semi-confined conditions beneath thick surface clay layers. The conceptual model is designed to be implemented in an Earth system modeling framework and is limited to the central portion of the aquifer in Brazos and Burleson Counties, Texas. Unlike previous models in ParFlow.CLM, this is a high-order subbasin with large inflows from upstream. Additionally, the model incorporates no-flow, transient head, and free drainage boundaries. Preliminary tests suggest the need for a long spin-up period. Long-term simulations will require calibration of surface and subsurface parameters before using the model to assess system behavior

Integrated Environmental Modelling Framework for Cumulative Effects Assessment

Global warming and population growth have resulted in an increase in the intensity of natural and anthropogenic stressors. Investigating the complex nature of environmental problems requires the integration of different environmental processes across major components of the environment, including water, climate, ecology, air, and land. Cumulative effects assessment (CEA) not only includes analyzing and modeling environmental changes, but also supports planning alternatives that promote environmental monitoring and management. Disjointed and narrowly focused environmental management approaches have proved dissatisfactory. The adoption of integrated modelling approaches has sparked interests in the development of frameworks which may be used to investigate the processes of individual environmental component and the ways they interact with each other. Integrated modelling systems and frameworks are often the only way to take into account the important environmental processes and interactions, relevant spatial and temporal scales, and feedback mechanisms of complex systems for CEA. This book examines the ways in which interactions and relationships between environmental components are understood, paying special attention to climate, land, water quantity and quality, and both anthropogenic and natural stressors. It reviews modelling approaches for each component and reviews existing integrated modelling systems for CEA. Finally, it proposes an integrated modelling framework and provides perspectives on future research avenues for cumulative effects assessment

Ecohydrological impacts of climate change on a riparian chalk valley wetland

This thesis assesses the impacts of climate change on the CEH River Lambourn Observatory, Boxford, UK. This comprises a 10 ha chalk valley, riparian wetland and 600 m of the River Lambourn, designated for its conservation value and scientific interest. A field campaign targeted knowledge gaps in previous research to enable development of a conceptual model of hydrological functioning. The physically based, distributed model MIKE SHE was chosen to simulate hydrology due to flexibility in process representation and proven applicability to wetland hydrology. Model results were consistent with field observations and confirmed the conceptual model. Findings showed that groundwater/surface-water interaction dominates hydrological processes. Channel head boundaries broadly control water levels across the wetland. Areas of groundwater upwelling control discrete head elevations and contain high concentrations of nitrate. These support confined growth of Carex paniculata surrounded by poor fen communities in reducing higher-phosphate waters. In-channel macrophyte growth and its management through cutting acutely affect water levels. Impacts of climate change were assessed by driving the MIKE SHE model with projected changes in hydrometeorological inputs for the 2080s, derived from UKCP09. Areas of groundwater upwelling caused amplified response of water levels at distinct locations. Simulated water levels were linked to requirements of the MG8 plant community and Desmoulin’s whorl snail (Vertigo moulinsiana). Impacts on each differed spatially, in line with hydrological impacts. The PHABSIM habitat modelling methodology was modified to assess river habitat response for brown trout (Salmo trutta), using outputs from the 1D hydraulic component of MIKE SHE, MIKE 11. Reductions in habitat availability were pronounced through periods of low flows, more so for adult than juvenile trout. Different hydrological requirements for species in distinct areas of the site support separate management strategies. Multiple objective management may be achieved through adaptive modification of the current management regime

FORECASTING CLIMATE AND LAND USE CHANGE IMPACTS ON ECOSYSTEM SERVICES IN HAWAIʻI THROUGH INTEGRATION OF HYDROLOGICAL AND PARTICIPATORY MODELS

Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018

A Case Study for Assessing the Hydrologic Impacts of Climate Change at the Watershed Scale

Since the advent of the industrial era atmospheric concentrations of greenhouse gases have been on the rise leading to increasing global mean temperatures. Through increasing temperatures and changes to distributions of precipitation, climate change will intensify the hydrologic cycle which will directly impact surface water sources while the impacts to groundwater are reflected through changes in recharge to the water table. The IPCC (2001) reports that limited investigations have been conducted regarding the impacts of climate change to groundwater resources. The complexity of evaluating the hydrologic impacts of climate change requires the use of a numerical model. This thesis investigates the state of the science of conjunctive surface-subsurface water modeling with the aim of determining a suitable approach for conducting long-term transient simulations at the watershed scale. As a result of this investigation, a coupled modeling approach is adopted using HELP3 to simulate surface and vadose zone processes and HydroSphere to simulate saturated flow of groundwater. This approach is applied to the Alder Creek Watershed, which is a subwatershed of the Grand River Watershed and located near Kitchener-Waterloo, Ontario. The Alder Creek Watershed is a suitable case study for the evaluation of climate change scenarios as it has been well characterized from previous studies and it is relatively small in size. Two contrasting scenarios of climate change (i.e., drier and wetter futures) are evaluated relative to a reference scenario that is based on the historical climatic record of the region. The simulation results show a strong impact upon the timing of hydrologic processes, shifting the spring snow melt to earlier in the year leading to an overall decrease in runoff and increase in infiltration for both drier and wetter future climate scenarios. Both climate change scenarios showed a marked increase to overall evapotranspiration which is most pronounced in the summer months. The impacts to groundwater are more subdued relative to surface water. This is attributed to the climate forcing perturbations being attenuated by the shift of the spring snow melt and the transient storage effects of the vadose zone, which can be significant given the hummocky terrain of the region. The simulation results show a small overall rise of groundwater elevations resulting from the simulated increase in infiltration for both climate change scenarios