| Abstrakt: |
On June 24, 2019, Congressman Raul Grijalva of Arizona, Chair of the House Committee on Natural Resources, sent a letter to the directors of the U.S. Fish and Wildlife Service and the U.S. Geological Survey to request their assistance in answering questions regarding coastal sediment resource management within the Coastal Barrier Resources System as defined by the Coastal Barrier Resources Act (Public Law 97–348; 96 Stat. 1653; 16 U.S.C. 3501 et seq.). For the purposes of this response, coastal sediment resource management refers to the removal of sediment from one part of a barrier island system for placement in another part of the coastal system, for either hazard mitigation (for example, erosion or flood control) or coastal restoration (for example, expansion or restoration of beach, dune, and [or] marsh habitats). The specific topics of concern are as follows (paraphrased from Congressman Grijalva’s letter): 1. Disruption of coastal sediment supply resulting from sediment removal and placement, including the replenishment rate of removed sediments and impacts to other components of the barrier island system (discussed in sec. 3). 2. Physical and biological impacts of sediment removal and placement on benthic habitats (discussed in sec. 4). 3. Impacts of sediment removal and placement on fish and other marine species (discussed in sec. 5). 4. Changes in migratory bird nesting and foraging habitats resulting from sediment removal and placement (discussed in sec. 6). 5. Long-term impacts of sediment removal and placement on physical coastal resiliency (discussed in sec. 7).To address these five topics, it is essential to begin with some background information about the terrestrial and submerged geomorphic components of coastal barrier island systems and the dominant physical processes that shape and connect them. Barrier islands and spits (referred to as barrier islands throughout the text) are wave-constructed landforms, typically parallel to the coast with a high-energy shoreline facing the open coast and a lowenergy shoreline along the lagoon or estuary. Barrier islands are dynamic and can change in size, shape, and behavior over time. Size and shape are mainly changed by the predominance of wave and (or) tidal processes and the balance between sediment supply and sea-level change. Given static sea level, a decrease in sediment supply might cause island narrowing, segmentation, and (or) rotation of the barrier island’s orientation, whereas an increase in sediment supply might cause increases in island height and width or in alongshore growth. If sediment supply is constant, increases in sea level will result in erosion and landward migration of the island (called “transgression”), whereas decreases in sea level will result in increases in barrier height and seaward movement of the shoreline (aggradation and progradation, respectively). Variations on these principal behaviors occur when sea level and sediment supplies are changing. Barrier island sediment dynamics today (2021) are largely sustained by natural and anthropogenic processes. Seasonal and storm-driven changes in wave and current energy and short- and long-term changes in water level and inlet dynamics result in natural sediment exchanges among barrier island environments (namely, the inner continental shelf, shoreface, beach, dunes, marsh, and estuary). Coastal sediments are moved within and among these environments by alongshore and cross-shore sediment transport processes. Sediment removal and placement activities contribute to these naturally occurring processes. The following subsections contain summaries of the consensus findings and research gaps that this report identifies as relevant to the five topics addressing sediment removal and placement impacts. It should be noted that, in addition to the physical and ecological focus of Congressman Grijalva’s inquiry, sediment removal and placement could also have economic, cultural, and recreational impacts, which, though beyond the scope of this review, could be important to consider in some locations within the Coastal Barrier Resources System. [ABSTRACT FROM AUTHOR] |
