Identifier

etd-06112014-140552

Degree

Doctor of Philosophy (PhD)

Department

Geography and Anthropology

Document Type

Dissertation

Abstract

This dissertation investigates the factors that control beach surface moisture dynamics. The study consists of a suite of laboratory and field experiments to document, analyze, and model the role of the key input parameters (groundwater table fluctuations, capillary actions (i.e., moisture retention, hysteresis, and hydraulic conductivity), evaporation-condensation, and sediment size) on the spatio-temporal variability of beach surface moisture content. Results from the laboratory experiments demonstrated that the capillary processes of hysteresis and hydraulic conductivity heavily influence the spatial and temporal dynamics of beach moisture. Additionally, different sediment grain sizes produced marked differences in capillary processes within the sediment column, under the same hydrological conditions. Analysis of evaporation dynamics reveals that evaporation from the beach surface differs dramatically from that of a free water surface. Initially, evaporation of moisture occurs almost entirely at the surface layer and at a rate that approximates the potential evaporation rate. However, after this time period the rate of evaporation at the upper surface layer stabilizes and remains approximately constant and the sub-surface layer becomes the dominant source of moisture for evaporation. Field measurements of surface moisture content demonstrated that spatially the beach surface can be characterized by three moisture-content zones: a consistently dry back beach zone, a variable content zone, and finally a persistently wet fore beach zone. Temporally, moisture contents varied over both short-term (daily) and long-term (multi-day) sequences. Over the short-term, diurnal fluctuations in the groundwater table played a significant role in influencing surface moisture across the wet and variable-content zones, whereas evaporation and condensation processes were the dominant factors in the dry zone. Over the longer term, variations in the lunar spring/neap tidal range produced distinct changes in the range of moisture contents, as it regulated the amplitude of the beach groundwater table over multi-day time scales. Modeling of surface moisture content demonstrated that a hysteresis based modeling approach provides a quite accurate and thorough representation of field-measured beach surface moisture dynamics. Simulations revealed that the inclusion of evaporation only influences predicted surface moisture contents across the dry back beach, whereas simulations across the wet fore beach and moisture variable middle beach are virtually unchanged by the inclusion of evaporation.

Date

2014

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Namikas, Steven L.

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