Graduation Year

2020

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geology

Major Professor

Jason Gulley, Ph.D.

Committee Member

Mark Rains, Ph.D.

Committee Member

Paul Moore, Ph.D.

Keywords

Bahamas, conduit, diagenesis, eogenetic, karst, permeability

Abstract

Lake-aquifer connectivity on carbonate platforms is governed by basin morphology which is influenced by diagenetic and depositional processes. Both these processes cause aquifer permeability to vary significantly with scale of measurement (i.e., pore-scale, well-scale, and regional-scale). Because coastal aquifers are well-known to have tidally controlled water level fluctuations, inland lakes may be used to expand the areal measurement of permeability and establish a link between well-scale and regional scale connectivity in the aquifer. To evaluate the impact of lake basin morphology on aquifer connectivity, water level fluctuations were collected at high temporal resolution in the ocean and twenty-four surface water bodies on San Salvador Island Bahamas. We estimated hydraulic diffusivity (transmissivity/storativity) values from dampened tidal amplitudes to establish a range of connectivity with the ocean. These diffusivity values were then used to estimate bedrock permeability. Apparent permeability of bedrock separating lakes from the ocean spanned from approximately 10-14.4 to 10-9.8 m2. Lower permeabilities were present in lakes that were connected primarily by matrix permeability, whereas higher permeabilities were present in lakes that were connected to a greater degree of conduit permeability. Our findings support bedrock permeability that increasingly scales with age. We suggest that the platform is heterogenous and compartmentalized, and vertical conduits enhance connectivity between lower permeability surficial bedrock and underlying higher permeability bedrock. Because most lakes lack conduits to puncture low permeability exposure surfaces, they contain a restricted connection with the groundwater system and readily precipitate evaporites in their basins.

Download

Share

COinS