Defining the Environmental Benefits of Dredged Sediments in Benefit-Cost Ratio Calculation

“Sustainable and effective ecosystem restoration and improved coastal resilience requires the effective use of sediment resources” - Gulf of Mexico Alliance (GOMA) Governor’s Action Plan

The Challenge

Storms, sea level rise, subsidence, disruptions to sediment supply, and other natural and anthropogenic disturbances are driving coastal erosion, habitat loss, and risk to communities throughout the Gulf of Mexico. Green or hybrid infrastructure solutions, including sediment placement to restore marsh, beach, and other habitats, have been increasingly recognized as an important tool for reducing or mitigating these losses. Widespread implementation of green infrastructure faces several challenges, however. Project alternative evaluation processes currently used by the U.S. Army Corps of Engineers and other entities often use a benefit-cost ratio (BCR) or incremental benefit analysis that relies on monetized valuation. Social, environmental, and economic benefits of sediment placement, such as the storm risk reduction provided by marsh or beach restoration, may be undervalued or excluded in BCR calculations due to a lack of readily available tools for robust valuation. Similar undervaluing of the role of sediment in the coastal system can lead to actions that inadvertently worsen problems they are attempting to address, such as borrowing of sediment from nearshore areas that are naturally supplying sand to adjacent shorelines. At the same time, competing and conflicting uses for sediment and nearshore/offshore areas where it’s found have combined with depletion of borrow areas to reduce the availability of quality material for placement. Our study goal is to define and demonstrate the positive outcomes associated with regional sediment management (RSM) and beneficial use of dredged material to support the efficient and effective use of sediment resources.

The Approach

The Institute is partnering with the GOMA Habitat Resources Team Regional Sediment Management working group to identify and evaluate benefits of beneficial use and RSM that are undervalued in BCR calculations, determine factors leading to increased benefits or reduced costs; and to develop best practice guidance for more comprehensively and accurately capturing those benefits. The project includes:

  • Establishing an advisory group of decision-makers, practitioners, and stakeholders involved with sediment placement in the Gulf of Mexico, who will provide subject matter expertise and input on sediment valuation;
  • Identifying 3-4 sediment placement and/or beneficial use case studies that are diverse in spatial scale, location, and types of habitat created (Gulf-facing beaches, barrier island restoration, marsh);
  • Reanalyzing the case studies for more comprehensive consideration of the benefits provided by sediment placement, including storm surge and wave attenuation; recreational use; and creation (or increases in the connectivity) of habitats of various types;
  • Evaluating the factors and efficiencies that led to overall cost reductions within the project, such as use of alternative dredging equipment;
  • Synthesizing the results across case studies and articulating best practices for quantifying the benefits and reducing the overall costs in projects and programs that include RSM and BUD.

This work will leverage completed and ongoing work the Institute has conducted in coordination with the USACE Engineering with Nature program on evaluating and accelerating implementation of Natural and Nature-Based Features; ongoing work the Institute is conducting with the U.S. Geological Survey to evaluate the cumulative effects of Deepwater Horizon restoration projects; and extensive work with the Louisiana Coastal Protection and Restoration Authority (CPRA) across multiple efforts in support of coastal restoration and sediment placement, such as the Barrier Island System Management program that includes consideration of the benefits of sediment placement and barrier island restoration as part of implementation of RSM in practice.

This project will provide practitioners with guidance that enables more widespread use of RSM and beneficial use of dredged material that is consistent with holistic management of sediment as a valuable and limited resource.