Sedimentation analysis

The karst Biscayne aquifer is characterized by a heterogeneous spatial
arrangement of porosity, making hydrogeological characterization difficult. In this
dissertation, I investigate the use of ground penetrating radar (GPR), for understanding
the spatial distribution of porosity variability in the Miami Limestone presented as a
compilation of studies where scale of measurement is progressively increased to account
for varying dimensions of dissolution features.
In Chapter 2, GPR in zero offset acquisition mode is used to investigate the 2-D
distribution of porosity and dielectric permittivity in a block of Miami Limestone at the
laboratory scale (< 1.0 m). Petrophysical models based on fully saturated and unsaturated.
water conditions are used to estimate porosity and solid dielectric permittivity of the
limestone. Results show a good correspondence between analytical and GPR-based
porosity estimates and show variability between 22.0-66.0 %.
In Chapter 3, GPR in common offset and common midpoint acquisition mode are
used to estimate bulk porosity of the unsaturated Miami Limestone at the field scale
(10.0-100.0 m). Estimates of porosity are based on the assumption that the directly
measured water table reflector is flat and that any deviation is attributed to changes in
velocity due to porosity variability. Results show sharp changes in porosity ranging
between 33.2-60.9 % attributed to dissolution areas.
In Chapter 4, GPR in common offset mode is used to characterize porosity
variability in the saturated Biscayne aquifer at 100-1000 m field scales. The presence of
numerous diffraction hyperbolae are used to estimate electromagnetic wave velocity and
asses both horizontal and vertical changes in porosity after application of a petrophysical
model. Results show porosity variability between 23.0-41.0 % and confirm the presence
of isolated areas that could serve as enhanced infiltration or recharge.
This research allows for the identification and delineation areas of macroporosity
areas at 0.01 m lateral resolution and shows variability of porosity at different scales,
reaching 37.0 % within 1.3 m, associated with areas of enhanced dissolution. Such
improved resolution of porosity estimates can benefit water management efforts and
transport modelling and help to better understand small scale relationships between
ground water and surface water interactions.

A simple model is developed to evaluate the acoustic scattering environment of sediments based on the envelope function of digital sub-bottom sonar data. Scattering pressure and intensity histograms are produced from model results. These histograms are compared to the theoretical distributions expected for scattering event pressure and intensity. Sediment composition is inferred from the determined acoustic scattering environment. The model has been applied to X-Star digital sub-bottom data taken in the vicinity of St. John's Harbor, New Brunswick. Model results are compared to ground truth (Borehole logs) taken within the survey area. This comparison indicates general trends within the sediment scattering environment which may be linked to sediment composition. Distinct differences in model results were noted over areas of differing sediment types.

The specific effects of sediment resuspension on the rate and amount of phosphorus diffusion by commercially available kaolinite and bentonite soils were examined in a laboratory setting by amending the soils with phosphorus fertilizer (46% P2O5), reacting them in a plexiglass container (by removing a partition) and allowing the soils to mix with the overlying water column as they spread along the container bottom. The concentration of total phosphorus was measured at 1, 3, 6, 12, 24 and 36 hours after reaction occurred. A computer program was written to calculate the diffusion coefficients (D) for the different soil and fertilizer treatments. Correcting the D values for adsorption resulted in effective diffusion coefficients (De) values, averaged across all retardation factors, of 0.010; 0.0017 and 0.0124 cm^2/day for the 13,944; 9,295 and 4,648 mu g/1 phosphorus fertilizer kaolinite treatments and 0.0002; 0.0006 and 0.0013 cm^2/day for the 13,654; 9,103 and 4,552 mu g/1 phosphorus fertilizer bentonite treatments. The diffusion coefficients for the kaolinite soil treatments were consistently greater than those for the bentonite treatments.

A thesis investigates the measured and theoretical pressure reflection coefficients of the seabed at normal incidence. The theoretical reflection coefficient is calculated using a physics-based model developed by Maurice Biot. The model describes sound propagation in saturated porous media and interrelationships between the acoustic properties of the media and the physical properties of the pore fluid and the porous solid. Stoll modified the Biot model for the case of ocean sediments and developed an expression for calculating the reflection coefficient as a function of frequency. This thesis tests the model by comparing the reflection coefficient measured with chirp sonar to the reflection coefficient calculated using the Biot model. An experiment was conducted off Fort Walton Beach, Florida where chirp sonar transmitted FM pulses at normal incidence to a sandy seabed. Sediment properties measured during SAX-99 are used to calculate the theoretical reflection coefficient using the Biot-Stoll model. The agreement of the measured reflection coefficients with the theoretical calculations over the band of 1500 to 16000 Hz varies as much as 70%. The plotted results show a reduction of the reflection coefficient with frequency but the large deviations from the trend prevent any further conclusions.