BIOPHYSICAL CONTROLS ON TIDAL CHANNEL DYNAMICS AT PLUM ISLAND ESTUARY, MASSACHUSETTS

Meandering tidal channels defined by bidirectional flows migrate across salt marsh platforms over time. However, it is not fully clear what biophysical factors might influence tidal channel migration rates and whether or not existing fluvial theory can be used to understand these patterns. Through a combination of field work, aerial imagery analysis, and examination of Spartina alterniflora belowground root biomass, we evaluated tidal channel controls on migration rates for five tidal channels over a 62-year period at Plum Island Estuary in northeast Massachusetts. We determined that bank slope, channel width, and vegetation cover (as indicated by the Normalized Difference Vegetation Index) impact the incidence of bank collapse. We also observed significant differences in the amount of belowground root biomass between two streams. Observed tidal channel migration rates for five streams in Plum Island Estuary were <0.01 channel widths per year. Our work highlights how channel width, geometry, and vegetation cover lead to greater tidal channel migration rates further upstream within the estuary. This study provides further evidence that the migration rates of tidal channels, when normalized for channel width, are governed by curvature in a similar manner as their fluvial counterparts. We also provide new evidence for how differences in Spartina alterniflora root biomass might be a significant control on migration rates for tidal channels.