Julie Dean Rosati

Quantifying coastal system resilience for the US Army Corps of Engineers

The US Army Corps of Engineers (USACE) is responsible for the management of the Nation’s water resource infrastructure and is presently challenged to continue the safe operation and management of that aging infrastructure. These challenges span from changes in climate patterns to increased environmental concerns, greater coastal population densities and associated infrastructure, and limited budgets. One way to mitigate these issues is the concept of resilience. In 2013, the Coastal Engineering Research Board (CERB) began to define resilience and understand its relation to coastal water infrastructure needs. This work was a step forward in facilitating the USACE’s integration of resilience into coastal engineering assessment and project design. The CERB has defined resilience using the four concepts of “prepare,” “resist,” “recover,” and “adapt.” These four concepts are utilized in a system-wide approach that encompasses not only water resource engineered infrastructure (that the USACE builds and manages), but also considers community and ecological infrastructure. Using this framework and literature from previous federal and academic studies, three methods were developed that incorporate different levels of expert and data-driven assessment. Two of these methods, herein named Tier 1 and Tier 3, were tested in a pilot study in Jamaica Bay, NY. Building off of the results from Jamaica Bay, Tier 1 is being refined and Tier 2 is in development.

ADVANCEMENT OF TECHNOLOGIES FOR PRACTICING REGIONAL SEDIMENT MANAGEMENT

The US Army Corps of Engineers (USACE) initiated the Regional Sediment Management (RSM) program in October 1999 to evaluate the implementation of regional approaches to sediment and project management within the USACE. The RSM Program has flourished from a single USACE District evaluation to a national paradigm shift which progresses the USACE from project scale management to regional management for both coastal and inland systems. Advancements in technologies in the areas of data collection, management, and analysis; numerical modeling; web-based tools; and communications have positioned the USACE to more efficiently and effectively implement regional approaches to improve our understanding of regional processes, share information and data, collaborate, and therefore improve decision making in the management of our sediments and projects. This paper discusses the methodology for implementing RSM, with an emphasis on advancements in technologies that have improved the USACE’s ability to implement regional approaches.

Beach Erosion: Causes and Stabilization

Natural and human-related causes of beach erosion are discussed and illustrated by examples. Sea level rise, trapping of sand by natural inlets and migration of natural inlets are the most pervasive natural causes. Construction of navigation works, followed by reduction in sediment delivery to the coast and subsidence induced by ground fluid extraction are the most prevalent human-related causes. Application of the Bruun Rule to sea level rise is discussed including its limitations and extensions to include beach nourishment and barrier islands. Prediction of shoreline changes caused by natural phenomena on decadal scales can only be accurately calculated with historical data. However, predictions of shoreline and volume changes due to human-induced effects such as construction of a littoral barrier or a beach nourishment project can reasonably be calculated with analytical and numerical models. Societal responses to beach erosion are expensive and limited to: retreat, stabilization with structures, nourishment and combinations of the last two. Each beach is unique thus placing a need to understand the cause of the erosion, develop a prognosis for “without response” conditions and prescribe the best approach for the future. Fortunately, long-term shoreline changes are available in some areas as are the effectiveness of some stabilization projects to guide this process. It is concluded that it will be possible to maintain some highly developed areas for one or two centuries with available technology and resources. Some areas will undoubtedly require abandonment within this period.

Alignment of U. S. ACE Civil Works Missions to Restore Habitat and Increase Environmental Resiliency

ABSTRACT The Civil Works mission area of the U.S. Army Corps of Engineers (USACE) spans multiple programs including navigation, flood risk management, infrastructure construction and operation, and environmental stewardship–including restoration and regulation of protected waterways. The national scope of USACE activities means that habitat preservation and restoration projects vary in size and type, while often intersecting spatially with projects under other USACE missions. This intersection can create management challenges that must be resolved. Two USACE initiatives, Engineering With Nature and Regional Sediment Management, explore and implement best practices that combine natural processes and restoration needs with management requirements. This article presents four case studies describing initiatives to 1) design, rehabilitate, and manage infrastructure in alignment with natural processes; 2) manage sediments on a regional scale to support the re-use of material removed from navigation channels for coastal and riverine resiliency, and 3) develop landscape-level plans for waterways management to support conservation efforts. The cumulative effect of multiple efforts to restore functionality lost through anthropogenic alterations and long-term geological change is expected to be a more resilient system at the landscape scale. However, challenges remain in quantifying resilience and the benefits provided by ecosystem services that are affected by management actions.

MODEL OF BARRIER ISLAND EVOLUTION AT DECADAL SCALE

A decadal-scale model is developed to represent evolution of barrier islands, inlets, and inlet deltas. Sensitivity tests of the model reproduce essential aspects of how barrier islands evolve depending on bay infilling or expansion. The model is applied to the fourinlet system in Barataria Bay, Louisiana, USA, in which the bay is known to have increased in surface area over the past 120 years due to regional subsidence, increase in sea level, and wetland loss. The increase in bay surface area increased the tidal prism and cross-sectional area of the tidal passes, extended the ebb tidal deltas farther offshore, and increased the ebb tidal delta volumes, resulting in erosion of the barrier islands. Starting from conditions in the 1880s, the decadal-scale model reproduces changes in ebb delta volume, inlet cross-sectional area, and island volume in agreement with previous conclusions that Grand Terre Islands will disappear within the next 30 years.

Merrimack Estuary and Newburyport Harbor sediment management studies

This report documents a numerical modeling study investigating sediment transport and morphology change adjacent to Merrimack Inlet, Newburyport, and nearshore in the vicinity of Salisbury Beach and Plum Island, Massachusetts. Concerns at the site include beach erosion, shoreline retreat on Plum Island downdrift of and within the inlet, and reduced navigability of the inlet. The numerical modeling evaluation consists of two phases. The Phase I study was conducted with the damaged and partially rehabilitated South Jetty between 2012 and 2014, and the Phase II study was conducted with the fully rehabilitated South Jetty between 2015 and 2016. Historical hydrodynamic and sediment data in the study area were assembled, and a field data collection program was carried out. The datasets were used to develop a coastal wave, hydrodynamic, and sediment transport model. Different alternatives were developed to evaluate sediment management strategy and structure modification, and the calculated bed sediment volume changes of each alternative were compared with the results under base (existing) condition. Alternative simulations demonstrated the Coastal Modeling System capability in evaluating beach erosion, structure performance, sediment transport, and morphology change in the inlet and estuarine system. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. ERDC/CHL TR-18-7 iii

Engineering with Nature: Nearshore Berm Placements at Fort Myers Beach and Perdido Key, Florida, USA

Abstract : Two nearshore berm nourishments were placed at Fort Myers Beach and Perdido Key Florida, USA, as part of Regional Sediment Management practices. At Fort Myers Beach, a bar-like berm was placed offshore, while at Perdido Key a swash-zone berm was placed approximately half-way between the mean water line and berm crest to maximize the potential for mobilization. Themorphologic and sedimentologic evolution of both study areas was documented based on beach profile surveys and sediment sampling. Both projects were successful in that they added sediment to the littoral system and dry beach, protected the natural beach from storm impacts, and equilibrated with the natural system making the placement site sustainable for future projects. The nearshore berm at Fort Myers Beach contained mixed sediment and fine material initially located in the trough landward of the berm migrated offshore, while coarser beach quality sediment moved onshore. Sediment at Perdido Key was beach-quality sand slightly finer than the native sand on the subaerial beach, and was successfully integrated over the two-year monitoring period.

CONCEPTUAL REGIONAL SEDIMENT BUDGET FOR THE U.S. NORTH ATLANTIC COAST

A Conceptual Regional Sediment Budget (CRSB) was developed for coastal beaches, bays and estuaries extending from Virginia to Maine, USA, as part of the North Atlantic Coast Comprehensive Study. Hurricane Sandy made landfall on October 30th, 2012 near Brigantine, New Jersey and generated severe beach erosion and property damage throughout this region. A CRSB is the first step in understanding sediment transport patterns and magnitudes, and aligning dredging and placement operations to take advantage of natural processes and identify sediment deficiencies in a regional system. Optimizing regional sediment management practices in this region is critical to (a) improve beneficial use of dredged sediments; (b) reduce the risks of future storm damage and enhance the environment; and (c) reduce costs in maintaining coastal infrastructure. Data from 1990-2013 indicated an average of 18.7 million cu yd/year was dredged within the North Atlantic region. The CRSB is accessible via a web portal.

Vulnerability and Impacts on Natural Resources

Climate change-mediated impacts originating from terrestrial and marine sources interact at the coast to influence coastal habitats (Nicholls et al., 2007; Rosenzweig et al., 2007; Figure 3-1; Table 3-1). On the landward side, increased temperatures and altered precipitation patterns interact with changing land-use and land-cover practices to affect soil moisture, ground water levels, hydrology, sediment supply, salinity, and pollution in watersheds. On the marine side, sea-level rise, changing ocean currents, increased wave heights, and intensification of coastal storms interact with changes in land use and land cover to exacerbate coastal erosion, flooding, and saltwater intrusion. As a result of these interactions, complex changes in coastal freshwater availability and water quality are also occurring.