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When longshore transport systems encounter tidal inlets, complex mechanisms are involved in bypassing sand to downdrift barriers. Here, this process is examined at Plum Island Sound and Essex Inlets, Massachusetts, USA. One major finding from this study is that sand is transferred along the coast—especially at tidal inlets—by parcels, in discrete steps, and over decadal-scale periods. The southerly orientation of the main-ebb channel at Plum Island Sound, coupled with the landward migration of bars from the ebb delta to the central portion of the downdrift Castle Neck barrier island, have formed a beach protuberance. During the constructional phase, sand is sequestered at the protuberance and the spit-end of the barrier becomes sediment starved, leading to shoreline retreat and a broadening of the spit platform at the mouth to Essex Bay (downdrift side of Castle Neck). Storm-induced sand transport from erosion of the spit and across the spit platform is washed into Essex Bay, filling channels and enlarging flood deltas. This study illustrates the pathways and processes of sand transfer along the shoreline of a barrier-island/tidal-inlet system and provides an important example of the processes that future hydrodynamic and sediment-transport modeling should strive to replicate. [ABSTRACT FROM AUTHOR]

The survival of salt marshes depends on their ability to maintain vertical elevation and areal extent. In the lateral direction, marsh edges can expand laterally or undergo edge erosion through mass failure or continuous particle erosion through waves and tidal processes. In this study, we evaluate possible relationships between marsh shoreline type within the Great Marsh in Massachusetts and major geotechnical parameters along the marsh edge. We also explore if wave energy, using fetch as a proxy, affects the presence, type, and distribution of shoreline type. We mapped and classified the marsh into four categories: slumping, vertical and abrading, stable/accretionary, and bedrock or gravel, and sampled the marsh edge at 98 sites. Using over 450 measurements, we present typical ranges of values at these marsh edges for bulk density (0.10–1.43 g/cm3), organic content (0.99–55.07%), belowground biomass (0.11–36.76%), and shear strength (4.04–136.49 kPa at 20 cm into the marsh bank, and 4.04–131.03 kPa at 40 cm into the bank). We show that there are no significant differences in fetch or geotechnical properties for the different marsh edge classes. Thus, none of these parameters explain or correlate with edge erosion, even though the majority of previous edge erosion studies focus on these parameters as determinants of edge erosion. We further emphasize the heterogeneity of the marsh, as edge erosion can occur in highly exposed or sheltered areas alike with no trends in geotechnical properties, and that complex interactions between parameters not generally studied may be responsible for edge erosion. • This large-scale field study examined the relationships among geotechnical properties, fetch, and edge erosion at over 90 sites. • Neither fetch nor the geotechnical properties of marsh banks explained the type and distribution of marsh edge erosion. • Previously identified parameters do not explain the observed system, suggesting more complex interactions are causing edge erosion. [ABSTRACT FROM AUTHOR]