Date of Award

Spring 2020

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

Committee Chairperson

Daria Nikitina, PhD.

Committee Member

Howell Bosbyshell, PhD.

Committee Member

Martin Helmke, PhD. P.G.

Abstract

Seasonal and decadal monitoring of salt marsh at Slaughter Beach, DE documented long-term and short-term variations in number and sizes of salt ponds. Over 400 salt ponds ranging in size between 0.5 m2 to 0.11 km2 were identified on 5.5 km2 salt marsh platform. The purpose of this study is to quantify hydrologic conditions and measure groundwater discharge of a salt marsh, particularly the impact of tidal forces on groundwater fluctuation.

Four wells with nests of mini-piezometers with ONSET Pressure Transducers were installed along a transect crossing the largest salt pond (0.11 km2) in the study area. Nests of wells, installed at depths of 1 m, 3 m, and 6 m recorded groundwater hydraulic head at five-minute intervals during a 90 day period. High resolution aerial imagery of the studied ponds was collected at peak high tide and low tide using an unmanned drone. Changes in groundwater elevation were correlated with tidal data recorded by the USGS stream gauge in Cedar Creek.

Our results document the presence of 2 aquifers; deep (3m) and shallow (1m). Relationship between groundwater elevation and tidal fluctuations is strong in the deep aquifer and weak in the shallow aquifer. Analysis of drone imagery reveal no changes in the shape or size of the pond during 1 tidal cycle. Groundwater elevation decreases in proportion to distance from Cedar Creek and decreases with depth. We suggest that the deep aquifer is confined. This study has established a baseline for hydrologic investigations within the salt marsh.

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