Date of Award

Spring 2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Committee Director

G. Richard Whittecar

Committee Member

Jennifer Georgen

Committee Member

Xixi Wang

Abstract

First Landing State Park, located in Virginia Beach, is a cuspate foreland developed from a succession of erosional and progradational events forming a series of dunes and interdunal swales. Low-lying swales dominate the southern portion of the park forming many wetlands, but the northern portion of the park has fewer wetlands. An asymmetric groundwater dome has been observed on Cape Henry, cresting north of the geographic center of the cuspate foreland. The purpose of this study was to determine if the wetlands that dominate the southern portion of the park are the major driver of the asymmetric groundwater dome and to determine if historic drought conditions have been dry enough to desiccate the wetlands within the park.

Using the White Method, the actual evapotranspiration (AET) rates were calculated for the two major vegetation groups, namely ponded wetlands and upland dunes, located on Cape Henry. A higher evapotranspiration (ET) rate was calculated for the wetland setting. A finite difference groundwater flow model called Wetbud was used to determine if the difference in evapotranspiration rates was large enough to shift the groundwater dome. Crop coefficients (Kc) were estimated using the AET rates calculated by the White’s Method and the potential evapotranspiration (PET) rates calculated by the Penman-Monteith method. These coefficients and ET rates were input into the Advanced (i.e., MODFLOW-based) model constructed in Wetbud. The modeling results suggest that the difference in ET between the two vegetation groups plays an important role in the formation of the asymmetric groundwater dome. However, because the White’s Method may underpredict the water loss from the wetlands, the ET differences may not be the only driver. Other factors could include lateral surface flow between the wetlands and surface runoff, both of which have not been accounted for in the model. Effective Monthly Recharge (Wem), a method to construct synthetic hydrographs, was used with a historic temperature record (1896-2018) from Cape Henry to infer the length and frequency of droughts at Cape Henry. Results from Wem indicate that seasonal droughts occur frequently at Cape Henry along with less frequent multiyear drought periods.

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DOI

10.25777/xwy4-jr07

ISBN

9781392236147

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