Characterization of Submarine Groundwater Discharge (hereafter referred to as SGD) and the development of empirical mathematical models and forecasting tools for the quantification of SGD in Baffin Bay, Texas is a critical ecological need. In areas like Baffin Bay, Texas, the quantification of the net water discharge had not taken place due to the remoteness and lack of attention, but never the less, these areas are still particularly sensitive to the availability of freshwater resources. The focus of this dissertation is centered on new and innovative methods to evaluate net groundwater discharge into the Baffin Bay, Texas. Previous studies have indicated that approximately “10 to 55 % of the total flux of freshwater into bays and estuaries are from SGD” (Burnett et al., 2001; Cable et al., 1996; Paulsen et al., 2001; Taniguchi et al., 2006). Therefore, if the net fresh groundwater input is not accounted for this could lead environmental engineers in the wrong direction to incorrectly account for only a fraction of the total freshwater inflows.
The materials and methods in this study included the implementation of a custom ultrasonic flowmeter apparatus capable of flow measurements at the minute timescale in both the forward and reverse directions placed under the surf of Baffin Bay, Texas. SGD data was downloaded and separated into fractions of freshwater and saltwater to determine the amount of freshwater entering Baffin Bay, Texas. Overall, temporal and spatial variations were observed intra-day as well as seasonally (e.g. intra-year) to characterize SGD at Baffin Bay Texas. The results indicated that the SGD at Baffin Bay, Texas is predominantly marine recirculated seawater, due to wave setups at Baffin Bay Texas, with approximately 25% of the SGD attributable to terrestrial freshwater. This initial and preliminary result discovered early on in the study lead to the development of models based on marine-ward based correlations between SGD relationships with water levels, barometric pressures, wind speeds, and wind directions. Factors such as measured water level fluctuations from the National Oceanic and Atmospheric and Administration (NOAA) buoys near Baffin Bay, Texas were correlated with SGD. Other factors were obtained from the Crop Weather Program (CWP) such as barometric pressures, wind speeds, and wind directions to evaluate their correlation as well with SGD. Based on the above initial and preliminary results, 92 initial possible correlations were tested and the results indicated that SGD and water levels and wind speeds were correlated more often than barometric pressures and wind directions. The scatter plots of the correlation coefficients indicated some potential for autocorrelation; however, future work could involve more rigorous testing the data for autocorrelation since several approaches are necessary to make an affirmative interpretation that the data is autocorrelated. >The magnitude of flow measurements indicated SGD varied from negative 16 cm/day to 48 cm/day amongst sampling campaigns and showed stochastic characteristics pointing towards marine seawater parameters affecting SGD. Overall, approximately 143 correlating models were tested in progressing model complexity (e.g. first testing the correlation with one variable then systematically including more variables) to see if the complexity would lower the Mean Squared Error (MSE) between SGD and water levels, barometric pressures, wind speeds, and wind directions obtained from NOAA or CWP using the correct proportionality, respectively.
The modeling results indicated that an increase in the number of inputs into the models enhanced the correlation between SGD and water levels, barometric pressures, wind speeds, and wind directions. Overall, correlations were observed between SGD and water levels, barometric pressures, wind speeds, and wind directions with positive, negative, or no correlation in some cases. These observed correlations are presented as well as an application of these correlations in a new approach towards modeling SGD using empirical mathematical models and forecasting tools for the quantification of SGD in Baffin Bay, Texas, yet to be applied in this field of study as well as suggesting these new parameters are incorporated into conventional SGD modeling. Although the study area in this dissertation was only based in Baffin Bay, Texas, additional locations should be evaluated with similar correlation testing investigations. This dissertation will demonstrate how SGD relationships with water levels, barometric pressures, wind speeds, and wind directions are correlated in Baffin Bay, Texas and how the development of empirically based mathematical models proved useful, before extending the research to other bays.
There were three main hypotheses presented in this work that were explored and tested. Hypothesis one (1) was to postulate that SGD does exist in Baffin Bay, Texas, and that the portion being freshwater can be estimated and quantified. Hypothesis two (2) postulates that SGD may be correlated with water levels, barometric pressures, wind speeds, and wind directions at Baffin Bay, TX. Hypothesis three (3) postulates that from this data a very preliminary evaluation of the use of the empirical mathematical models and forecasting tools for the quantification of SGD in Baffin Bay, Texas testing the correlation between SGD and water levels, barometric pressures, wind speeds, and wind directions could offer new and insightful relationships for modeling SGD as well as suggesting new modeling forcing functions.
September 26, 2014
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