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In 1993 concerns were expressed by English Nature that Devon's three largest sand dune systems Braunton Burrows, Northam Burrows and Dawlish Warren were drying out to the detriment of the dune habitat flora and fauna. Research was therefore required to understand how these systems functioned hydrologically, to determine whether they were drying out and if so to recommend sustainable management options aimed at reinstating former water levels, or preventing any further lowering of the water tables. At Braunton water table elevations have been monitored on a monthly basis by the Nature Conservancy, the Nature Conservancy Council and English Nature since 1972. These data were invaluable in describing the spatial and temporal hydrological characteristics and functioning of the groundwater system. Braunton Burrows was the main study site of the research. At both Northam and Dawlish, at the start of the fieldwork programme a dipwell monitoring network was installed and water table elevations were recorded weekly. Hydrological characteristics of each dune system were related to temporal variability in effective precipitation, the tide, the underlying geology and sediment properties. The groundwater system at Braunton was mounded, with effective inputs accumulating over an impermeable basal layer close to mean sea level. The system was very sensitive to seasonal variability in effective precipitation. At the centre of the groundwater mound, during the winter months, the elevation of the water table was 10 in above OD. The groundwater mound was asymmetric, with the highest water table elevations occurring along the eastern margin of the system. The transitional zone from dune sands to marshland, of a lower permeability, was restricting the inland lateral drainage regime and was controlling both the shape and elevation of the water table. At Northam the groundwater system was also mounded and again the shape and elevation of the water table were dependent upon effective precipitation. Unfortunately the monitoring network at Dawlish proved insufficient to describe either the shape or elevation of the groundwater table. Within the smaller systems of Northam and Dawlish variable sediment properties lead to intra-site variability in annual cyclical water table fluctuations. A prominent trend in the long-term water table data for Braunton Burrows was the general overall decline in the elevation of the water table from 1983 to mid 1992. With precipitation as the primary source of groundwater recharge, consecutive years with below average effective precipitation (1983-1992) was undoubtedly the primary cause, but was exacerbated by the drainage improvement works carried out on West Boundary Drain in 1983. Scrub growth, artificial drainage of the golf course and marine erosion were also possibly influencing the groundwater drainage regime. At Northam and Dawlish, without historical data it was not possible to determine if the systems were drying out, however factors influencing annual cyclical water table elevations were identified. Again climate was the key variable controlling the long-term elevation of the water table and undoubtedly the dry spell between 1983 and 1992 would have had repercussions on the elevation of the water table within these two systems. At Northam the drainage ditch network and reduced tidal inundation were the other main factors influencing groundwater levels. At Dawlish the golf course pump drainage system and scrub encroachment were effectively reducing annual groundwater recharge. At Braunton a numerical groundwater flow model was used as a predictive management tool, to assist in the recommendation of sustainable water level management options. A range of commercial groundwater flow models were reviewed and Visual MODFLOW, incorporating the original United States Geological Survey's MODFLOW code, with a fully integrated pre and post processor, was selected as the most suitable model for the Braunton scenario. The modelling exercise had three objectives; to test whether a commercial model such as Visual MODFLOW could be applied successfully to simulate the hydrology of Braunton Burrows; to gain further detail on the hydrological functioning of the system and ultimately if the model was calibrated to test a set of management scenarios to predict the hydro-ecological consequences of introducing new management practices into the system. Having identified the most probable factors influencing water table elevations within each dune system, sustainable hydrological management options were recommended with the aim of raising water levels, or preventing any further decline in water table elevations. The management options afforded nature conservation the highest priority, but also took into consideration the long-term requirements of all the other land user groups.A t Braunton when formulating the managemenrt ecommendationst he modelling predictions were also taken into consideration. Potential areas for future research were also identified. Water level monitoring should continue at all three sites, so that the longer-term impact of any water level management strategies implemented as a result of this research can be evaluated. Also at both Northam and Dawlish a more detailed analysis of the geology and sediment properties would be invaluable in providing a more comprehensive hydrological description of the functioning of the groundwater systems. The Braunton groundwater model could be developed further, addressing and overcoming problems encountered in this study and evaluating a wider range of water level management scenarios. As a result of this research far more is understood about the hydrological functioning of Devon's three largest dune systems and the recommendation of sustainable remedial/restorative water level management options will help to ensure that these ecologically diverse habitats are conserved for future generations. This research has also provided both the applied and theoretical framework to address water resource management problems within small and large scale dune systems around the shores of Great Britain.

A dissertation submitted to the Faculty of Science in fulfilment of the requirements for the degree of Master of Science November 2015, Johannesburg / South Africa is faced with water quantity and quality issues in most catchments. Intensification of coal-based industrial activity in the Waterberg, Limpopo and the concomitant emissions of oxides of nitrogen (NOX) and sulphur (SOX) pose potential ecological impacts to regional freshwater systems. Some research indicates that a significant proportion of minerals in the Waterberg parent rock may be prone to acid generation with catchment soils being potentially susceptible to acidification via NOX and SOX deposition. Cultural and recurrent nutrient loading of freshwater bodies also impacts on primary production and can ultimately alter the natural structure and functioning of these ecosystems. Trend analyses on historical hydrological data from 1982 to 2013 were carried out for several response water quality variables from six quaternary Waterberg catchments. Results were assessed for possible changes attributable to increased NOX and SOX loading post commencement of large-scale coal combustion. Historical inorganic N:P ratios were calculated in conjunction with a series of nutrient (N and P) bioassay experiments to predict which nutrient may be limiting growth of stream periphyton. Although trends were identified in most catchments for several of the water quality variables, the notion that the onset of large scale coal combustion has led to noticeable downward trends in pH and upward trends in either inorganic N or sulphate is not unequivocal. Patterns in trends were not distinct for catchments situated in close proximity to the primary emission source and those further away. Nor were there any distinct differences in trends between upwind and downwind catchments. Climate and geo-hydrological factors are likely to still function as the primary drivers of spatial and temporal variation in past and present catchment water quality. Contrary to the view that stream primary production is limited largely by the availability of P, predictions based on N:P ratios calculated in this study suggest N to be the limiting nutrient. This was shown to be the case in four of the five study-site rivers. N-limitation increased by 18% (67% to 85%) in the Matlabas River post-commencement of large-scale coal combustion. A greater increase of 24% (60% to 84%) was observed in the Middle Mokolo. Although cultural eutrophication levels in the Waterberg do not yet exceed management-set targets, the cumulative effect of industrial-derived nutrient inputs remains a threat to the nearshore marine ecosystem and human communities living downstream.

Karst aquifers are vulnerable to contamination, as conduits and fractures in the aquifers are preferential flow paths where contaminants move fast. On the other hand, the presence of conduits and fractures make groundwater modeling for karst aquifer a challenge. This dissertation addresses several important issues related to groundwater contamination, numerical modeling, and equipment development with potential applications in karst. In Chapter 2, I discuss groundwater contamination in the karst aquifer of Yucatan, which is the only source of drinking water for the population of Yucatan but groundwater in the top of the aquifer has been polluted and cannot be used for human consumption. I developed a new statistical method to analyze temporal and spatial variation of groundwater quality in the aquifer. By using this method, I identified the factors that cause temporal and spatial changes in the groundwater quality as well as the zones of influence. The spatial changes are caused by the following factors: interaction between groundwater and matrix rock, distribution of precipitation, seawater intrusion, mixture of water rich in sulfates, and human pollution in two zones within the study area. The temporal variation is caused by changes in the amount and distribution of precipitation. The new method proves to be important for deriving information about the temporal and spatial processes affecting groundwater quality. Chapter 3 is focused on validating the MODFLOW CFP M1 model developed by the U.S. Geological Survey for simulating groundwater flow in karst aquifers. The model validation process is important to build confidence for using the model. I was interested in quantifying to what extent the model can accurately simulate groundwater flow in karst conduit and surrounding porous media, in other words, if the equation used to simulate the flow exchange between karst conduits and surrounding porous media was suitable for this experiment. The model validation was done using results of lab experiments. A sandbox lab device was developed to understand three-dimensional (3-D) groundwater flow in a confined karst aquifer with a conduit in the middle of the aquifer. Thirteen lab experiments were performed. Hydraulic heads and flow rates of the conduit and surrounding sand were measured. I used three experimental results to calibrate the roughness of the conduit, hydraulic conductivity of the sand surrounding the conduit, and a coefficient used by MODFLOW CFP M1 for simulating the flow exchange. Using the calibrated model, I evaluated the estimated errors (the difference between model simulations and the corresponding data) along with the 95% confidence intervals for the true error. The errors were calculated for flow rates at the inflow and outflow of the sandbox and the heads in the porous media. The confidence intervals consider measurement error, model calibration error, parameter uncertainty, and propagation of the measurement error in the boundary conditions. The results of model calibration and validation showed that the magnitude of the error was highly correlated with the magnitude of measured flow exchange, indicating that MODFLOW CFP M1 cannot adequately capture the physics of the flow exchange. Therefore, MODFLOW CFP M1 is valid when the flow exchange is small but invalid otherwise for this sandbox experiment. In Chapter 4, I developed a seepage meter to measure groundwater seepage from groundwater to surface waterbodies such as a lake. I was interested in verifying the accuracy of an analytic solution, which estimates the seepage through the bottom of a lake, using measurements from a sandbox experiment. However, existing methods were not useful in this case because of the small scale. Therefore, I proposed a new seepage meter useful for this case. The proposed seepage meter can be used to estimate the hydraulic conductivity as well. Therefore, I tested: (1) the accuracy of the seepage meter using a Darcy column, and (2) the accuracy of the analytic solution using a MODFLOW model and seepage measurements from a sandbox. This sandbox represents an unconfined aquifer with groundwater discharge into a lake. The new seepage meter consists of a cylinder inserted into the lake bed. The groundwater seepage is directed first to the cylinder and then to an external reservoir where seepage measurements are made. The laboratory results show that the seepage meter can be used to measure seepage for the laboratory experiment. However, more tests are needed to further evaluate the accuracy of the seepage meter. The numerical results show that the analytic solution is a good approximation for seepage estimation. Chapter 5 discusses the conclusions of my dissertation research and the research in future studies. / A Dissertation submitted to the Geophysical Fluid Dynamics Institute in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2017. / July 14, 2017. / Groundwater Quality, Karst, Model validation, MODFLOW CFP, Seepage meter, Yucatan aquifer / Includes bibliographical references. / Ming Ye, Professor Directing Dissertation; Gang Chen, University Representative; Xiaoming Wang, Committee Member; Nicholas Moore, Committee Member; Bryan Quaife, Committee Member.

Low Impact Development (LID) techniques for site design are increasingly being utilized to mitigate the negative impacts associated with stormwater runoff, and green roofs are one such application. The ability of green roofs to reduce the total and peak volumes of stormwater runoff has been fairly well documented, but performance varies in different climate zones, and there is limited information available regarding green roof effectiveness in New England, a region whose weather patterns are notoriously variable from season to season and often even day-to-day. Additionally, there are questions regarding the impact that green roofs have on water quality, especially regarding phosphorus. While many green roofs have been found to leach phosphorus into stormwater runoff within the first few years after installation, it is assumed that this phenomenon will not continue after the green roof vegetation has been established. However, it is still unclear whether or not this assumption is valid, and very few research projects have focused on providing the necessary insight into the hydrologic and geochemical processes that are contributing to this observed problem. The Nitsch/Magliozzi Green Roof, located atop WPI's newest residence hall, was donated to enhance the sustainability of the building and to foster continued research and education. This roof provided an opportunity to better characterize the relationship between rainfall and runoff volumes, phosphorus sorption/desorption in the growing medium, and plant uptake processes. Comparisons of grab samples of stormwater from both the green and non-green portions of the roof within the first few seasons following installation confirmed that phosphorus was leaching into the runoff, and some seasonal trends were observed. For example, the highest concentrations (3-13 mg/l P-PO4-3) were observed during an especially rainy summer. In order to gain a better understanding into the nature of this occurrence, laboratory experiments on sections of this same green roof were designed and set up in WPI's greenhouse. A series of simulated rainfall events were conducted, a mass balance approach was used to analyze flow, and the phosphorus content of the water, plants, and soil were assessed. For flow attenuation, the green roof panels performed as expected under different rainfall and antecedent moisture conditions. Additionally, the greenhouse experiments provided improved insight into the nature of the relationship of phosphorus between the flow conditions, plant uptake, and soil processes, as well as its distribution throughout a storm. The laboratory data further provides a basis for estimating performance of a green roof and its long-term impact on stormwater quality. In a broader context, the findings also serve to inform future extensive green roof designs and subsequent research efforts.

Natural radioelements and inert gases in solution in groundwaters have been applied to problems of groundwater flow and age measurement. The 4He content of groundwaters generally increases with age and in the Bunter Sandstone, Nottinghamshire, the 4He contents of groundwaters have been linearly related to 14C ages. In the Lincolnshire Limestone, the He contents of the groundwaters have been used to indicate mixing of recharge water and interstitial water. In the other study areas, 4He and 40Ar in groundwaters have been used as qualitative indicators of age. The 4He contents of core samples have been related to the 4 He contents of the interstitial water and the formation depth. 4He diffusion in confined and non--confined sedimentary structures has been discussed. The amounts of non-radiogenic inert gases dissolved in groundwaters have been used to estimate groundwater recharge temperatures. In the Bunter Sandstone, these have been related to palaeoclimatic history by calibrating with the 14C ages. Estimated recharge temperatures have also been related to seasonal recharge, changes in the altitude of recharge and to variations in the hydrogen and oxygen isotopic ratios. Variation of the 222Rn contents of groundwaters has been used as an indicator of aquifer variability. The relative importance of intergranular and fissure flow and the variation in efficiency of 222Rn release into groundwaters has been investigated. The fraction of 222Rn released from rocks has been determined and the mechanisms by which 222Rn is released from sandstone, limestone and granite rock fragments has been discussed. Variability of the 226Ra contents of groundwaters has been explained in terms of the relative importance of the recoil and etch mechanisms of solution and the solubility of 226Ra salts in groundwaters.

The mechanism of Rn solution in groundwaters has been studied in both laboratory simulations and in field situations. The effect of sporadic and seasonal changes in rainfall patterns on the Rn contents of perennial springs in the Mendip Hills has been investigated. The separate contributions of surface streams, soil zone residence and percolation within the rock formation have been identified. The relative importance of fissure or conduit and percolation flow in the aquifer have been shown to determine the nature of the response of Rn content to rainfall patterns. An examination of the Rn contents of air in limestone caverns has established that intergranular diffusion of Rn from below the rock surface is the primary reason for Rn release into the air space. Rn transport and release from stream inflows is relatively unimportant. Experimental determinations of the Rn diffusion coefficient in rock sections have shown that such intergranular diffusion is much more significant than intragranular diffusion. Laboratory studies of Rn release from fragmented rock samples have been used to determine the efficiency of radon release for different rock types. These studies have also confirmed that intergranular diffusion is an important process by which groundwaters acquire high Rn contents. The Ra content of geothermal groundwaters from Iceland have been determined. The Ra and U contents of calcite deposits from various depths within these geothermal systems are discussed in relation to changes in the Ra geochemistry. Rn contents have also been determined for groundwaters from the Berkshire Chalk and are shown to be dependent upon the extent to which porewater mixing has occurred.

This study explores seasonal patterns and structures of moisture transport pathways from the North Atlantic Ocean and the Gulf of Mexico that lead to extreme large-scale precipitation and floods over land. Storm tracks, such as the tropical cyclone tracks in the Northern Atlantic Ocean, are an example of moisture transport pathways. In the first part, North Atlantic cyclone tracks are clustered by the moments to identify common traits in genesis locations, track shapes, intensities, life spans, landfalls, seasonal patterns, and trends. The clustering results of part one show the dynamical behavior differences of tropical cyclones born in different parts of the basin. Drawing on these conclusions, in the second part, statistical track segment model is developed for simulation of tracks to improve reliability of tropical cyclone risk probabilities. Moisture transport pathways from the North Atlantic Ocean are also explored though the specific regional flood dynamics of the U.S. Midwest and the United Kingdom in part three of the dissertation. Part I. Classifying North Atlantic Tropical Cyclones Tracks by Mass Moments. A new method for classifying tropical cyclones or similar features is introduced. The cyclone track is considered as an open spatial curve, with the wind speed or power information along the curve considered as a mass attribute. The first and second moments of the resulting object are computed and then used to classify the historical tracks using standard clustering algorithms. Mass moments allow the whole track shape, length and location to be incorporated into the clustering methodology. Tropical cyclones in the North Atlantic basin are clustered with K-means by mass moments producing an optimum of six clusters with differing genesis locations, track shapes, intensities, life spans, landfalls, seasonality, and trends. Even variables that are not directly clustered show distinct separation between clusters. A trend analysis confirms recent conclusions of increasing tropical cyclones in the basin over the past two decades. However, the trends vary across clusters. Part II: Tropical cyclone Intensity and Track Simulator (HITS) with Atlantic Ocean Applications for Risk Assessment. A nonparametric stochastic model is developed and tested for the simulation of tropical cyclone tracks. Tropical cyclone tracks demonstrate continuity and memory over many time and space steps. Clusters of tracks can be coherent, and the separation between clusters may be marked by geographical locations where groups of tracks diverge due to the physics of the underlying process. Consequently, their evolution may be non-Markovian. Markovian simulation models, as often used, may produce tracks that potentially diverge or lose memory quicker than nature. This is addressed here through a model that simulates tracks by randomly sampling track segments of varying length, selected from historical tracks. For performance evaluation, a spatial grid is imposed on the domain of interest. For each grid box, long-term tropical cyclone risk is assessed through the annual probability distributions of the number of storm hours, landfalls, winds, and other statistics. Total storm length is determined at birth by local distribution, and movement to other tropical cyclone segments by distance to neighbor tracks, comparative vector, and age of track. An assessment of the performance for tropical cyclone track simulation and potential directions for the improvement and use of such model are discussed. Part III: Dynamical Structure of Extreme Floods in the U.S. Midwest and the United Kingdom. Twenty extreme spring floods that occurred in the Ohio Basin between 1901 and 2008, identified from daily river discharge data, are investigated and compared to the April 2011 Ohio River flood event. Composites of synoptic fields for the flood events show that all these floods are associated with a similar pattern of sustained advection of low-level moisture and warm air from the tropical Atlantic Ocean and the Gulf of Mexico. The typical flow conditions are governed by an anomalous semi-stationary ridge situated east of the US East Coast, which steers the moisture and converges it into the Ohio Valley. Significantly, the moisture path common to all the 20 cases studied here as well as the case of April 2011 is distinctly different from the normal path of Atlantic moisture during spring, which occurs further west. It is shown further that the Ohio basin moisture convergence responsible for the floods is caused primarily by the atmospheric circulation anomaly advecting the climatological mean moisture field. Transport and related convergence due to the covariance between moisture anomalies and circulation anomalies are of secondary but non-negligible importance. The importance of atmospheric circulation anomalies to floods is confirmed by conducting a similar analysis for a series of winter floods on the River Eden in northwest England.

Quantification of risk to natural disasters is a valuable endeavor from engineering, policy and (re)insurance perspectives. This work presents two research efforts relating to meteorological risk, specifically with regard to storm surge hazard estimation and wind vulnerability assessment. While many high water level hazard estimation methods have been presented in the literature and used in industry applications, none bases its results on disaggregated tidal gauge data while also capturing the effects of the evolution of storm surge over the duration of a storm. Additionally, the coastal destruction wreaked by Hurricane Sandy in 2012 prompted motivation to estimate the event’s return period. To that end, this dissertation first presents the motivation for and development of the clustered separated peaks-over-threshold simulation (CSPS) method, a novel approach to the estimation of high water level return periods at coastal locations. The CSPS uses a Monte Carlo simulation of storm surge activity based on statistics derived from tidal gauge data. The data are separated into three independent components (storm surge, tidal cycle and sea level rise) because different physical processes govern different components of water level. Peak storm surge heights are fit to the generalized Pareto distribution, chosen for its ability to fit a wide tail to limited data, and a clustering algorithm incorporates the evolution of storm surge over surge duration. Confidence intervals on the return period estimates are computed by applying the bootstrapping method to the storm surge data. Two case studies demonstrate the application of the CSPS to coastal tidal gauge data. First, the CSPS is applied to tidal gauge data from lower Manhattan. The results suggest that the return period of Hurricane Sandy’s peak water level is 103 years (95% confidence interval 38–452 years). That the CSPS estimate is significantly lower than previously published return periods indicates that storm surge hazard in the New York Harbor has, until now, been underestimated. The CSPS is also applied to all tidal gauge stations managed by the National Oceanographic and Atmospheric Administration (NOAA) for which the hourly water level time histories are at least 30 years long. Comparison to NOAA’s exceedance probability levels for these stations suggests that the CSPS estimates higher return levels than NOAA, but also that the NOAA values fall within the 95% CI from the CSPS for more than half of the stations tested. This dissertation continues with a critical comparison of windstorm vulnerability models. The intent of this research is to provide a compendium of reference curves against which to compare damage curves used in the reinsurance industry. The models tend to represent specific types of construction and use varying characteristic wind speed measurements to represent storm intensity. Wind speed conversion methods are used to harmonize wind speed scales. The different vulnerability models analyzed stem from different datasets and hypotheses, thus rendering them relevant to certain geographies or structural typologies. The resulting collection of comparable windstorm vulnerability models can serve as a reference framework against which damage curves from catastrophe risk models can be evaluated.