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Master of Science (MS)
Grossman, Eric E.
Wallin, David O.
Estuarine wetlands have proven a cost-effective buffer against coastal hazards because they reduce erosive wave energy and enable sediment retention by producing hydraulic friction. Human modifications to coastal hydrology and sediment transport have resulted in loss of wetlands and associated protection. Our study area, the Stillaguamish Delta has experienced a 55% loss in wetlands and significant marsh retreat (Grossman and Curran (in review)). We quantified vegetation characteristics (spatial, vertical and, seasonal) that effect wave attenuation using image analysis, remote sensing and, in-situ measurements. We produced a sediment budget for the northern region and evaluate suspended sediment dynamics. Our elasticity and Side-On Photo analyses indicated dominate bulrush species maintained rigidity and biomass through January. Our classifications of hyperspectral imagery delineated vegetation assemblages with an overall accuracy of 76.9%. From biomass patterns, we predict the highest potential winter wave attenuation to occur within the first 0.5-0.75m of vegetation from the marsh floor and within the first 50m of the marsh edge. The highest winter sediment deposition coincided with highest biomass predictions, up to 300m inland. We observed the Low Marsh had been incorporated into the tidal flat by November and the lower Mid-Marsh (BOMA), the winter marsh edge, to have decreased in biomass to 25%. From these patterns, we hypothesize that the Low Marsh and lower Mid Marsh serve critical roles during the early monsoon season while the upper Mid-Marsh (BOFL) and High-Marsh become more influential during large and late season (Jan-Mar) storm events. Overall deposition is estimated to be 2.6% of the Stillaguamish River’s daily sediment load. Turbidity data indicated a delayed response to the river and showed relationships to regional wave generating winds.
Western Washington University
Stillaguamish River Delta (Wash.)
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Stellern, Chad D., "Emergent Wetland Plant Biophysical Characteristics Associated with Wave Attenuation and Sediment Retention" (2016). WWU Masters Thesis Collection. 542.