Date of Award

Winter 2024

Project Type

Thesis

Program or Major

Ocean Engineering

Degree Name

Master of Science

First Advisor

Tracy L Mandel

Second Advisor

Thomas C Lippmann

Third Advisor

Diane L Foster

Abstract

Salt marshes are effective sediment traps and under static sea levels are known to increase in elevation over time. However, current sedimentation rates are insufficiently high to keep up with the estimated sea level rise. Strategies such as the mud motor, which proposes the injection of dredged sediment into incoming flood tides, require a deeper understanding of how tidal flows evolve in complex estuarine systems and how suspended sediment is dispersed and deposited in vegetated environments. Two field deployments occurred in the summer of 2023 to study the mechanisms of sediment transport and accretion along a horizontal marsh transect in the tidally driven Hampton-Seabrook Estuary salt marsh in Southern New Hampshire. Three measurement stations were established in the high marsh, low marsh, and mudflat, each with two vertically separated YSI turbidity sensors and one Nortek ADV. Results showed that marsh vegetation attenuates flows, increases the vertical extent of turbulence, homogenizes turbidity in the water column within the marsh, and creates an environment prone to settling suspended sediment. Additionally, an overall increase of vertically homogenized turbidity in the low marsh relative to the mudflat was observed. These observations represent a first of their kind to measure an array of horizontal and vertical variations of flow and sediment dynamics in a tidal salt marsh.

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