Graduation Year

2007

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Mark T. Stewart, Ph.D.

Co-Major Professor

H. Leonard Vacher, Ph.D.

Committee Member

Mark Rains, Ph.D.

Keywords

permeameter, grain-size, Floridan, leakance, recharge

Abstract

A wetland in west-central Florida was studied to characterize the local hydrostratigraphic configuration of surficial deposits overlying more-permeable limestones and conceptualize groundwater recharge. Eight continuous cores were drilled through the surficial deposits and partially into the underlying limestone. A total of 111 samples were extracted from the cores for laboratory sediment analyses and testing. The surficial deposits are roughly eight meters thick and made up of upper and lower clean-sand hydrostratigraphic layers (S1 and S3, respectively) separated by a low-permeability layer of clayey sand (S2). Also, a discontinuous low-permeability layer of clayey sand (S4) lies between S3 and the top of limestone. Equivalent hydraulic conductivity values for the S2 and S4 clayey layers (0.01 and 0.1 m/day respectively) are significantly less than those of the S1 and S3 sand layers (2 and 1 m/day respectively).Significant confinement between the surficial and Upper Floridan aquifers by means of a laterally extensive dense-clay unit immediately above the limestone is consistently reported elsewhere in the region, but was not encountered within the wetland. Partial confinement is apparently the result of low-permeability layers within the surficial deposits alone. Results of ground-penetrating radar and vertical head difference measurements suggest the presence of buried sinkhole features which perforate the low-permeability S2 layer and create preferred pathways for flow or karst drains. Comparison of results between laboratory sediment testing and a site-scale aquifer performance test (APT) suggest that the primary mechanism for drainage during the APT was by vertical percolation through the S2 layer while flow through karst drains was minimized. In this case, calculated leakances based on laboratory sediment testing are most accurate in approximation of effective leakance.It is predicted that as water table stages rise within the wetland, effective leakance will increase as flow toward karst drains becomes the more dominant mechanism for drainage. As a result, calculated leakances based on direct laboratory sediment testing are a decreasingly accurate approximation of effective leakance.

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