Date of Award

Fall 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Ocean and Earth Sciences

Committee Director

G. Richard Whittecar

Committee Member

Joseph H. Rule

Committee Member

Donald Swift

Call Number for Print

Special Collections LD4331.O35 R435 2013

Abstract

False Cape State Park in southeastern Virginia Beach, Virginia contains a transgressive barrier island complex. Inter-dune swales located on the eastern coast of the barrier island contain soils that experience hydric conditions. However, these swales lack the prolonged presence of hydric soil indicators that are necessary for a site to be officially recognized as a jurisdictional wetland. The appearance and subsequent disappearance of redoximorphic wetland soil features in the young, sandy soils of the inter-dune swales here may stem from changes in the patterns of groundwater recharge and discharge across the island. These soils are being monitored by the Mid Atlantic Hydric Soils committee and features there may be proposed for formal recognition as hydric soil indicators.

Hydraulic head data indicate that a strongly asymmetric freshwater lens crests under the eastern half of the island. The asymmetric shape of the water table could be due to differences in either vegetation cover or permeability of stratigraphic packages. The densely-vegetated western half of the island experiences higher rates of evapotranspiration (ET) than the more open-canopied eastern half. Permeameter testing and grain size analysis indicates slight differences in the permeability and grain size between the soils of each respective island half. Stratigraphic analyses of ground penetrating radar (GPR) data suggest the upper beds of the island have relatively minor permeability contrasts that will not significantly affect shallow groundwater flow patterns in models and in the field. Analyses of annual-scale groundwater variation made using a MODFLOW - based package showed that the asymmetric shaped water table depended mostly on spatial variation in permeability and recharge. Results of groundwater models indicate that the spatial differences in ET are the dominant factor controlling the shape of the barrier island water table. Historic hydrographs created for the inter-dune swale demonstrate that regardless of the wetness period, the swale almost always experiences wetland hydrology conditions. This study may ultimately aid in the development of inter-dune hydric soil indicators.

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DOI

10.25777/1edv-7p98

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