Abstract not available.

Interactions between surface water systems and groundwater systems are poorly understood. This research focuses on the surface water/groundwater interactions that use an electric conductivity and temperature (EC&T) drag probe in the Raisin River and South Nation Watershed. To find groundwater seepages into rivers, a Reelogger Model 2001 probe (Solinst Canada Ltd) was dragged at the sediment-water interface to measure EC&T for several reaches of the Raisin River, the Castor River, the East Castor and the South Nation River. GPS position data was collected at the same time as the EC&T measurements which allows the data to be input into a GIS database for management decisions. During the summer, groundwater typically had higher EC and lower T values than the surface water, and so increases in EC occurring along with lower water temperatures were inferred to be deep-groundwater discharge locations. High EC values can be explained either by deep groundwater discharge (seeps) or by local anthropogenic loading of sediments into the river. In rivers with low permeability clay streambeds very few locations of significant discharge were detected using this method. The most significant discharge area, called the "Swimming Hole" by local residents, was surveyed at large and small scale and groundwater seepage was found to be present along the shore and in the middle. However, the EC&T probe appears to have identified relatively high flux discharge zones in the Castor and East Castor River at locations where highly permeable eskers cross the rivers. The survey identified approximately a 50 m area along the Castor river and a 100m area along the East Castor River where EC values were as high as 2000 muS/cm and temperature as low as 11°C. They were investigated and fluxes quantified by installing and testing piezometers and deploying seepage meters.

Terrestrial moisture fluxes associated with plant growth represent one of the largest movements of mass and energy in the Earth's outer spheres, yet the relative contributions of abiotic water vapor fluxes and those that are regulated solely by the physiology of plants remains contentious and poorly constrained. Herein, based on the interpretation of the stable isotopes of water as tracers of evaporation, a methodology for partitioning total evaporation (ET) into its constituent fluxes is developed. This methodology enabled the separation of evaporation from soils and water bodies (Ed), canopy evaporation (I n), and plant transpiration (T) and was developed for the Fly River watershed (∼76,000 km2), situated in a rainforest-dominated region of central New Guinea and then subsequently applied to thirteen other watersheds in North America, South America, Africa, and Australia. Estimates of the annual water balances for the selected watersheds suggest that T is the dominant water vapor flux in 'water-limited' regions, comprising approximately 67% of ET and 55% of P. Moreover, these regional estimates of T co-vary with P in a manner similar to that observed for independent estimates of net primary productivity (NPP), suggesting that similar to small-scale measurements of plant water-use, water vapor and carbon dioxide fluxes are inherently coupled and the flux of water vapor to the atmosphere during photosynthesis is several orders of magnitude larger than the corresponding sequestration of atmospheric carbon. Similar estimates of a partitioned terrestrial water vapor flux are scarce beyond this study and hence the results are informative, emphasizing the inter-dependency between solar radiation and terrestrial processes and the considerable uncertainty that is currently associated with these aspects of the Earth system. Although admittedly first-order in scale, the estimates offer a broadly conceptual perspective on the dynamics of energy exchange between terrestrial systems and the atmosphere, whereby the terrestrial carbon cycle is essentially driven by solar energy via the water cycle intermediary. In order to constrain the sources of dissolved constituents in the Fly River watershed, additional data pertaining to the carbon isotope composition of dissolved carbon in river was collected. Monthly samples were collected for a period of two years and higher-resolution data was collected over a period of several weeks in 2007. These data suggested that the dissolution of carbonate minerals in the watershed were the predominant source of dissolved constituents and that constituents related to the dissolution of silicate minerals were negligible by comparison.

A lineament analysis for Georgetown, Maine, a 44 km$\sp2$ island community situated on the central Maine coast, was performed to evaluate the relationship between mapped lineaments and (1) outcrop fractures, (2) well productivity (35 wells), and (3) groundwater quality determined from a sample of 87 existing bedrock wells. Lineaments were drawn by three observers using two scales of imagery (SLAR and a 1:80,000 Aerial Photograph). Rigorous reproducibility testing indicates that the ability of individual observers to reproduce lineaments at the same geographic location is low; more than 55% of all lineaments mapped by any observer were not reproducible. This casts doubt as to how many lineaments may be considered real features. In addition, when azimuthal sets of near-vertical outcrop fractures are compared with reproducible lineament domains of similar azimuth on a regional basis, distinct areas of overlap are defined across the island. The extent of this overlap is not uniform. Some lineament domains (165$\sp\circ$) exhibit no correlation with fracture fabric whereas other lineament domains (120$\sp\circ$) only show a correlation with fracture fabric in a very limited geographic area. In regard to well productivity, wells located "on" lineaments, specifically those lineaments showing a geographic correlation with similar-trending fracture domains, are generally more productive than non-lineament wells. If the same analysis is repeated, but is performed without considering whether or not the lineaments used in the analysis are geographically correlative with fracture domains, no differences are observed between the productivities of lineament and non-lineament wells. However, in this study, other geologic factors exhibit strong influences on high productivity in bedrock wells. Bedrock type (amphibolite) is the dominant and only statistically significant influence on well productivity followed by depth to the water table (shallow depths), proximity to lineaments (specifically those that correlate geographically with outcrop fractures), topographic position (flatter hydraulic gradients), and proximity to surface water bodies, in order of decreasing importance. Groundwater chemistry is controlled primarily by bedrock type, topographic setting, structural position, and overburden type and thickness. The chemical character of groundwater sampled from bedrock wells is generally not influenced by the proximity of a well to a lineament.

The dissertation reports a series of hydrological studies that relates to seawater intrusion in a karst aquifer. In the Woodville Karst Plan (WKP), karst conduit system is well developed and directly open to the Gulf of Mexico that allows seawater intrudes into the aquifer. The Spring Creek Springs Complex and Wakulla Spring, located in a marine estuary and 11 miles inland, respectively, are the two major groundwater discharge spots and connected through subsurface conduit network in the Woodville Karst Plain (WKP), North Florida, USA. Investigation of seawater intrusion in the Woodville Karst Plain is the objective and motivation of this dissertation work. Potential evidence of the longest documented seawater intrusion through conduit network in the Woodville Karst Plain (WKP) is found by the data analysis of electrical conductivity and chemical measurements. Five periods of increased electrical conductivity have been observed in the karst conduits supplying water at Wakulla Spring, one of Florida's largest first magnitude springs. A composite analysis of rainfall, electrical conductivity and geochemical data provides strong evidence that the increases in conductivity are directly tied to saltwater intrusion occurring at the Spring Creek Springs through the conduit network. This interpretation is supported by the conceptual model established by prior researchers, and represents the first and longest documented case of saltwater intrusion through conduit network in the WKP. Several numerical models are able to simulate the density-dependent seawater intrusion issue. On the other hand, discrete-continuum numerical models are designed to simulate groundwater flow and solute transport in a dual-permeability karst aquifer. However, none of the pre-existed code or model is able to deal with the two issues together. Therefore, a hybrid discrete-continuum numerical model of Variable-Density Flow and Solute Transport - Conduit Flow Process (VDFST-CFP) is developed as a new modeling method that provides more accurate simulation of seawater intrusion in a coastal karst aquifer with conduit network. Darcy-Weisbach equation is applied to simulate non-laminar groundwater flow in the conduit system. Density-dependent groundwater flow with appropriate density terms in both the conduit and porous media systems are analytically derived, then coupled with transport equations and solved numerically using finite difference method with an implicit iteration procedure. Two synthetic two-dimensional cases are developed to validate the newly developed VDFST-CFP model by comparing with other numerical models. The VDFST-CFP model improves simulations of density-dependent seawater/freshwater mixing processes and exchanges between the two domains. In comparison with the discrete-continuum models, Darcy equation of the continuum numerical models overestimates the flow rate but the VDFST-CFP is accurate under turbulent flow condition. The pros and cons of model uncertainties, assumptions, conceptual simplifications and numerical techniques of the VDFST-CFP are discussed. Several studies of numerical modeling have been done as an important method to evaluate seawater intrusion in coastal karst aquifers with conduit network, since field observations are usually insufficient. A regional groundwater flow cycling numerical model is developed to provide a general understanding of the flow regime that controlled by seawater/freshwater interaction in the WKP, using a discrete-continuum CFPv2 model. Non-laminar flows in conduits and flow exchange between the two domains are coupled in the hybrid numerical model. The time-variable salinity and equivalent freshwater head at the submarine spring have significant impacts on seawater/freshwater interaction and discharges of springs. Simulated results match well to measurements with correlation coefficients 0.891 and 0.866 at Spring Creeks Springs and Wakulla Springs, respectively. The impacts of sea level rise on regional groundwater flow field and the relationship between the two springs are evaluated as well by the numerical model. The controlling factors of seawater intrusion in a dual-permeability are evaluated by local and global parameter sensitivity analysis with a two-dimensional SEAWAT model, which also estimates the extents of seawater intrusion in the WKP. The local sensitivity study indicates the salinity at the submarine spring is the most parameter to simulations in both the conduit and porous medium, which are effective to all parameters near the mixing zone. The results of global sensitivity analysis exhibit similar pattern with the local study but are different for some parameters due to their non-linear relationship to the simulations. Simulations in the porous medium are sensitive to not only matrix parameters but also conduit conditions because of the conduit-matrix interaction. Dispersivity is important in a homogeneous porous medium model but is no longer significant in an advection-dominated karst system. The effects of the identified important parameters on the extents of seawater intrusion are quantitatively evaluated by examining the variation of salinity at the submarine spring with rainfall recharge, sea level rise and longer simulation time under an extended low rainfall period. / A Dissertation submitted to the Department of Earth, Ocean and Atmosphere Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / February 16, 2016. / Data analysis, Karst aquifer, Non-turbulent conduit flow, Numerical modeling, Seawater intrusion / Includes bibliographical references. / Bill Hu, Professor Directing Dissertation; Ming Ye, University Representative; Stephen Kish, Committee Member; Doron Nof, Committee Member.

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No description available.

A cohesive sediment bed model was implemented in the Community Sediment Transport Modeling System (CSTMS) to examine processes influencing sediment erodibility and suspended sediment concentrations. Estimates of eroded mass from the sediment bed model were calibrated and verified with erosion chamber measurements from the York River, Virginia, a tidally-dominated environment. A constant erosion rate parameter combined with depth-varying critical shear stress was sufficient to model erosion observations of depth-limited sediment cores. Sensitivity of total eroded mass to seasonal variations in erodibility and changes in consolidation time scale was evaluated during spring-neap variations in bottom stresses. Differences were greatest during spring tide and varied by as much as a factor of 2.5. Consolidation created an asymmetry between the spring-to-neap and neap-to-spring transitions with more sediment being eroded during the decreasing phase of maximum tidal stress. Consolidation time scales controlled the magnitude of this asymmetry with larger asymmetries occurring when slower consolidation time scales were assumed. Eroded mass estimates were potentially as sensitive to uncertainties in the consolidation time scale as they were to observed seasonal variability in critical stress. The cohesive sediment bed model was then implemented within a numerical model of the York River Estuary to examine feedbacks between sediment ux convergence and erodibility. Model results show the development of a highly erodible pool of sediment near the ETM location. Even when sediment convergence processes were diminished, suspended sediment concentrations remain high due to high sediment erodibility. Sediment concentrations and erodibility exhibited high spatial variability in both the along and across channel directions. As opposed to the results of the one-dimensional model, sediment concentrations and erodibility estimates were less sensitive to variations in the consolidation rate than to the initial bed conditions. Model calculations of sediment concentrations and erodibility showed similar patterns to observational data.

Quantitative evidence supplied by bottom sediment textural analysis, Fourier grain-shape analysis and Q-mode factor analysis indicate that river-borne sand-sized sediment originating in the upper reaches of the Rappahannock is actively transported downstream and ultimately delivered to the estuarine sediment regime. Current velocity observations in the upper estuary as well as suspended sediment concentrations measured at stream gaging stations, indicate that short-term extreme hydrological events such as periodic river flooding provide a plausible transport mechanism to move river-borne sands into the estuarine sediment regime.Events of this nature can disrupt average partly-mixed estuarine circulation patterns by displacing the salt-wedge to a more seaward position, increase stratification and create a net-seaward river-type flow within the affected portions of the estuary; thus, allowing high concentrations of river-borne sediments associated with the high freshwater inflow to move into the estuary and become incorporated into the estuarine sediment regime. Bottom sediment textural analysis indicates that the two major landward sources of sand-sized sediment to the Rappahannock Estuary are the Piedmont-derived river sands and sand-sized sediment derived from the constant denudation of fastland bluff sediments which directly outcrop along certain reaches of the Rappahannock River. Sand-sized sediment is consistently present within all the bottom sediment samples taken from the estuary channel as well as along its flanking shoals. Fourier grain-shape analysis serves to differentiate the Piedmont-derived river sands from the fastland bluff sands in that the sand-sized sediment derived from each of these provenances possess highly contrastable shape attributes. Based upon the distribution of Fourier harmonic amplitudes of ninety-four sand-shape samples over a defined range Fourier harmonic amplitude class intervals, it is found that the river sands and fastland bluff sands represent two statistically non-similar sand-shape populations. The distribution of Fourier harmonic amplitudes also suggests that these two non-similar sand-shape populations mix together within the river's active transport system landward of the Rappahannock Estuary. The proportional mixing of these two sand-shape populations and subsequent downriver transport results in the delivery of both shape populations into the estuarine sediment regime where they may become deposited and/or redistributed within the estuarine sediments. Q-mode factor analy��is is employed in order to determine the relative extent of the proportional mixing of the two non-similar sand-shape populations within the active transport system of the Rappahannock River-Estuary via the grain-shape information supplied by Fourier analysis. Q��mode analysis determined that three compositionally distinct end-members, or factor components, are sufficient enough to encompass 98.5% of the total grain-shape variance contained within the distribution of Fourier harmonic amplitudes for the ninetyfour sand-shape samples. Based upon the distribution these samples within the defined factor (variable) space, it is quantitatively determined that various percentages of the Piedmont-derived river sands are present within the bottom sediments of the Rappahannock Estuary both in the estuary channel as well as along its flanking shoal areas. Thus, Fourier grain-shape analysis proves as a useful geological tool in that it quantitatively determines that river-borne sand-sized sediment is present within the Rappahannock estuarine sediment regime.

No description available.