Sediment Dynamics

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.

 

McLachlan, R.L., Ogston, A.S., Allison, M.A., 2017. Implications of Tidally-Varying Bed Stress and Intermittent Estuarine Stratification on Fine-Sediment Dynamics through the Mekong’s Tidal River to Estuarine Reach. Continental Shelf Research.

Ogston, A.S., M.A. Allison, R.L. McLachlan, D.J. Nowacki, and J.D. Stephens. 2017. How tidal processes impact the transfer of sediment from source to sink: Mekong River collaborative studies. Oceanography 30(3):22–33, https://doi.org/10.5670/oceanog.2017.311.

Stephens, J.D., Allison, M.A., Di Leonardo, D.R., Weathers III, H.D., Ogston, A.S., McLachlan, R.L., Xing, F., Meselhe, E.A., 2017. Sand dynamics in the Mekong River channel and export to the coastal ocean. Continental Shelf Research. 


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.

McLachlan, R.L., Ogston, A.S., Asp, N.E., Fricke, A.T., Nittrouer, C.A., GomeS, V.J.C. (in review). Impacts of Tidal-Channel Connectivity on Transport Asymmetry and Sediment Exchange with Mangrove Forests

Controls of tidal channel connectivity on sediment flux into Amazonian mangrove forests – Ocean Sciences Meeting, February 2018,  Portland, OR.


Drainage-Channel Network Geometry in Muddy Mangroves

While studies of in-situ dynamics can shed light on how coastal regions are developing today, exploration must reach deeper into sedimentary deposits to understand how these environments have developed through time and more accurately predict how they will develop in the future. This study links modern and historic sediment dynamics by characterizing feedbacks between observed channel morphology and sediment deposits. The geometry of drainage channel networks was found to be a promising tool for interpreting modern sediment dynamics and relative aggradation rates in muddy mangrove forests; drainage channels that are relatively small and dense indicate that the region is aggrading at a more rapid rate.

McLachlan, R.L., Ogston, A.S., Asp, N.E., Fricke, A.T., Nittrouer, C.A., GomeS, V.J.C. (in prep). Drainage-channel network geometry as a tool for interpreting morphodynamics of mangrove forests and tidal channels.