National Academies of Sciences, Engineering and Medicine Gulf Research Program

Transport Thresholds for Fine Sediment in Vegetation

3 years

The Challenge

The primary objective of this project was to develop a standardized data collection methodology for monitoring fine sediment transport and retention within marsh vegetation so that marsh sedimentary function can be compared between different marshes, and across different marsh types (e.g. freshwater vs. salt, nascent vs. established). This methodology offers coastal restoration practitioners guidance on the most important hydrodynamic parameters to collect that are influential to fine sediment deposition, and how to integrate hydrodynamic, suspended sediment, and vegetation data to provide a coherent picture of marsh sedimentary function.

The Approach

A specific effort was made to ensure that data collected with the developed methodology could be easily incorporated into physics-based numerical models that are frequently used in coastal restoration applications (e.g. Delft3D, ADH/SEDLIB). Numerical modeling is a critical component of the planning process in many restoration projects, and is also included in the monitoring plans of well-designed projects with long term monitoring strategies. Sediment retention in coastal marshes is a key goal of many restoration projects on the Gulf Coast and elsewhere so it is important to design monitoring strategies that can provide usable and standardized calibration data for morphological models of vegetated regions.

The product of this project was a standardized methodology to guide field data collection efforts so that sediment transport and retention can be compared between marshes. The methodology addressed site selection, horizontal positioning of data collection with respect to the sediment and water source, vertical positioning with respect to the bed and the prevailing vegetation height, sampling frequency with respect to vegetation and hydrologic cycles, and standardized practices for reporting hydrodynamic and vegetation information in mutual context.

Critically, the methodology also provided guidance to applied numerical modelers on the model parameters (e.g. grid size, turbulence length scales, etc.) that are necessary to represent field conditions. The methodology was collected in a Vegetation Sediment Dynamics Monitoring Manual, and presented at a workshop to the coastal restoration community.