Suspended-Sediment Dynamics in the Tidal River to Estuarine Reach
Within estuaries, competition between river and tidal flows produces changes in estuarine regime and sediment dynamics. These changes range from long-term climate shifts to seasonal discharge fluctuations to daily spring-neap tidal cycles. This study analyzes how fluvial and marine factors interact and control sediment transport and channel morphology, linking near-bed shear stress and fine-grained particle aggregation to sediment resuspension and deposition throughout the range of fluvial and marine processes within a large tropical delta.
Dynamical Impacts of Tidal-Channel Connectivity
Flows within the most extensive mangrove forests tend to be driven through channels that connect to multiple estuaries or other channels with temporally lagged tides. For this study, in-situ observations of water and sediment flux were obtained in two tidal channels near the Amazon River to characterize how connectivity impacts sediment transport in coastal mangrove forests. As restoration efforts of mangrove forests continue to grow in response to coastal threats such as sea-level rise and diminished fluvial-sediment delivery, the timing and location of these efforts can benefit from the conclusion that channel connectivity influences both the spatial dispersal and the temporal availability of sediment supply to mangrove forests.
Controls of tidal channel connectivity on sediment flux into Amazonian mangrove forests – Ocean Sciences Meeting, February 2018, Portland, OR.
Sequence Morphodynamics in a Back-Barrier Tidal Channel
Understanding how back-barrier environments infill and evolve is necessary to predict how these regions will respond to future changes in sea-level and sediment supply. With this motivation, we interpreted in-situ observations and sedimentary signatures from an Amazonian tidal-channel system to create a conceptual model of past sequence morphodynamics in a mangrove-vegetated back-barrier environment. We find that a high-connectivity channel’s narrowest stretch will migrate along the path of net-sediment flux toward regions with more accommodation space until it reaches the flood-convergence zone. The location of recent preferential infilling is evidenced by rapid sediment-accumulation rates, relatively fine sediment, and clustering of small secondary tidal channels.
McLachlan, R.L., Ogston, A.S., Asp, N.E., Fricke, A.T., Nittrouer, C.A. (in review). Sequence Morphodynamics in a Back-Barrier Tidal Channel. Sedimentology.
Drainage-Channel Network Geometry: A Tool to Interpret Mesoscale Morphodynamics of Muddy Mangrove Channels – Gordon Research Conference and Seminar on Coastal Ocean Dynamics, June 2019, Manchester, NH.
Robin McLachlan 
