Best Practices for Physical Process and Impact Assessment in Support of Dredging Operations on the U.S. Outer Continental Shelf

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The Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE; previously Minerals Management Service [MMS]) Sand and Gravel/Marine Minerals Program is responsible for the environmentally responsible management of federal Outer Continental Shelf (OCS) sand and gravel resources. BOMRE’s mission is to make timely, streamlined, environmentally sound and fiscally responsible decisions about access to OCS sand resources. The increasing demand for sand for coastal restoration and protection will lead to a corresponding increase in the importance of these OCS resources through dredging/mining of sand borrow areas, as well as maintenance and expansion of navigation channels.  BOEMRE must continue to ensure that any use of OCS sand resources will not adversely affect the physical and biological environments, both in the near-field of the borrow site, as well as in the far-field near the coast.

The Applied Coastal team completed a comparative analysis of different process-based morphodynamic modeling packages that describe sediment transport and morphological changes under the action of waves and currents. The candidate models included public domain community models developed by various researchers in the United States – Community Sediment Transport Modeling System (CSTMS) and Nearshore Community Model (NearCoM) - as well as commercial models from DHI Water and Environment, Inc. and the United States Army Corps of Engineers (USACE).

Initially, a thorough review and collation of existing datasets, relevant information from previous studies domestically and abroad, and available guidance was completed. Then, models were applied to assess their predictive ability against observed morphology. As part of this initial effort, a series of sensitivity tests were performed for all candidate models to assess the influence of key input decisions, such as model formulation, model-specific settings, spatial resolution, a simplified parameterization or compression of environmental forcing, and the application of “speed-up factors” to increase the effective forecasting period of the models. Numerical models were run using a range of demonstrative borrow area geometries (aspect ratio, relative depth of cut) and ambient seabed conditions (flat, ridged) for both typical and storm forcing. Finally, a suitable framework and set of indicators and criteria were developed to provide best practice guidance that for general application along the U.S. Atlantic coast.