Coastal habitats bear the brunt of global environmental change. Rising sea levels, intense shoreline development, and pollution all contribute to worldwide habitat losses on the order of 1% to 7% per year. Cumulatively, nearly half of the world’s wetlands, mangroves, and seagrass habitats have eroded away over the past several decades.
Coastal ecosystems serve as vital carbon sinks and storm buffers while also providing critical habitat for countless species, both rare and abundant. To protect and maintain both natural and developed shorelines, scientists and landscape planners need reliable models on how water, sediment, and vegetation interact in coastal environments.
For years, so-called sediment transport models relied on measurements of bed shear stress; however, recent studies indicate these models underestimate the amount of material transported through plant-laden waterways. Specifically, the models do not account for the turbulence plants create in flowing water. In response to these shortcomings, Yang and Nepf propose a new framework for modeling sediment transport along vegetated shorelines and floodplains.
The authors developed an alternative method that relies on turbulent kinetic energy to predict the rate of sediment transport in vegetated zones. They conducted experiments in a 1-meter-wide by 10-meter-long flume that recirculated water and sediment while they varied the amounts of model plants and water velocity in the flume.
Upon successfully developing a model for vegetated regions, the authors tested their work in conditions lacking vegetation, scenarios that the bed shear stress model typically captures well. The results of the follow-up experiments suggest that the turbulence models also successfully predict sediment movement in unvegetated channels; in some cases, the new model worked even better than the standard model.
When taken together, the results from both the vegetated and bare-channel experiments indicated that turbulence is a better universal predictor of sediment flow than bed shear stress. The findings represent a significant advance in the field of coastal hydrology and geomorphology. The newly developed model should improve predictions of sediment transport and retention in both vegetated and unvegetated regions while improving restoration and planning in coastal environments. (Geophysical Research Letters, https://doi.org/10.1029/2018GL079319, 2018)
—Aaron Sidder, Freelance Writer