Beneficial use of dredged sediment as a sustainable practice for restoring coastal marsh habitat

Abstract

Abstract Coastal Louisiana (USA) continues to sustain immense land and habitat losses due to subsidence, sea-level rise, and storm events. Approximately 65 million m3 (85 million cubic yards) of sediment is dredged annually from Gulf Coast federal navigation channels to maintain safe waterway passage. The beneficial use of these sediments continues to increase, and now this sediment is recognized as a critical resource in large-scale (estimated multibillion dollar) ecosystem restoration efforts to mitigate land and habitat losses along the US Gulf Coast. However, the documentation of restoration benefits where dredged sediments are the primary resource is lacking, which limits the potential for future applications. Therefore, this study documents the progress to restore marsh habitat and the resultant benefits in West Bay, Louisiana, and investigates how the restoration practices align with principles of the US Army Corps of Engineers (USACE) Engineering with Nature® (EWN®) and UN Sustainable Development Goals (UN SDGs). West Bay, a 4964-ha subdelta adjacent to the Mississippi River, typifies risks of coastal land loss that also threatens the integrity of the adjacent federal navigation channel. To help restore coastal marsh habitat on a large spatial and temporal scale, the USACE constructed an uncontrolled diversionary channel from the Mississippi River and with subsequent direct and strategic placement of dredged sediment. Restoration performance was assessed through remotely sensed methods using data spanning approximately 70 years. To date, placement of dredged sediment in the bay has facilitated the creation of over 800 ha of new land in the formerly open waters of West Bay. The West Bay restoration project aligns with the principles of the EWN initiative, which supports more sustainable practices to deliver economic, environmental, and social benefits through collaborative processes and meaningfully integrates 10 of the UN SDGs designed to achieve a better and more sustainable future. Integr Environ Assess Manag 2022;18:1162–1173. Published 2021. This article is a U.S. Government work and is in the public domain in the USA. KEY POINTS The beneficial use of dredged sediment from Gulf Coast federal navigation channels continues to increase and is now being used as a means of restoring coastal ecosystems to mitigate land and habitat losses along the US Gulf Coast due to subsidence, sea-level rise, and storm events. This study documents the progress to restore marsh habitat in a 4,964-ha subdelta and the resultant benefits in West Bay, Louisiana and investigates how these restoration practices align with principles of the USACE Engineering with Nature® (EWN®) and UN Sustainable Development Goals (UNSDGs). From 2005 to 2020, direct sediment placement activities in West Bay have contributed to an increase in 646 ha of land, while nature-based features have contributed to an additional 292 ha of land area. The West Bay project provides a more complete understanding of project successes such that these techniques can be integrated into other dredging projects in coastal Louisiana and elsewhere.

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