Date of Award

Summer 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

Jennifer Georgen

Call Number for Print

Special Collections LD4331.O35 D63 2013

Abstract

In the Piedmont region of Virginia, development pressures are increasing the demand for mitigation wetlands but appropriate construction sites are relatively scarce due to local topography and geology. Many existing water budget models used for planned mitigation sites exhibit considerable error when estimating groundwater fluxes, particularly for historical years that lack hydraulic head data. This difficulty has led many planners to neglect or underestimate the contribution of groundwater to wetland water budgets, resulting in mitigation sites that fail to create the appropriate hydrology for the desired vegetation community. However, reliable estimations of groundwater input contributing to wetland water budgets can be generated by coupling models that reconstruct historic hydrographs (e.g. Effective Monthly Recharge (Wem) model) with mass balance water budget models that account for soil storage ( e.g. WetBud, development in progress). Using these models to simulate years that represent a range of hydrologic conditions (e.g. wet, normal, and dry years) can provide planners with critical information regarding the contribution of specific water budget inputs such as groundwater input.

Two case studies of natural toe-slope wetlands located in the central Piedmont of Virginia demonstrate the Wem is effective in predicting monthly head elevations for wells in Piedmont hillslope and toe-slope landscape positions (NSE > 0.84). Predicted head levels for wet, normal, and dry years were used in the calculation of groundwater input using Darcy's Law. Monthly water budgets generated using the WetBud Basic Scenario tool for two wet, two normal, and two dry years at each wetland reveal that groundwater input accounts for approximately 20% of total water budget inputs on any given year, regardless of total precipitation. However, seasonal variations in the relative contribution of groundwater to water budget inputs suggest that local floodplain morphology is the major factor influencing hydrology at each site. Overall, this study demonstrates that when coupled with the Effective Monthly Recharge (Wem) model, the WetBud Basic Scenario tool provides a practical platform that can be used to reliably predict the contribution of groundwater to wetland water budgets for years that lack observed water level data.

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DOI

10.25777/b4bk-7c04

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