Abstract Nature-based solutions (NbS) are increasingly recognized as effective tools for climate adaptation, yet their implementation remains limited by the perception that engineering guidance is lacking. This paper examines the existing spectrum of available guidance, ranging from informal case studies to peer-reviewed literature and state-level manuals, highlighting the need to clarify which types of standards are most useful across project types and contexts. Drawing on historical precedents, current practices, and recent advances in evaluating performance, we argue that a body of data and design knowledge exists but is decentralized and underutilized. We propose the creation of a Natural Infrastructure Engineering Hub (HUB) to centralize NbS resources, support adaptive learning, and promote the development of NbS-specific guidance that can evolve as more projects are designed, built, and monitored. Through cross-sector collaboration and phased implementation, the HUB offers a pathway to scale NbS with confidence, rigor, and transparency.

Design alternatives for traditional infrastructure are often compared in terms of expected–and often narrowly defined–costs and benefits to justify the selected plan. Taking a broader life cycle perspective in the benefit-cost evaluation process helps account for potentially rare, indirect, or accruing project benefits. Natural infrastructure design alternatives are generally difficult to compare to conventional alternatives due to their distinctly different costs and benefits. Natural infrastructure differs from conventional infrastructure in terms of performance and benefit development over time, lifespan, materials, intensity of intervention needs, and social and environmental benefits. This paper presents a life cycle framework that expands conventional life cycle analysis to capture other important and relevant aspects of natural and conventional infrastructure, enabling a more complete and equitable comparison of project costs and benefits. The framework consists of four dimensions: risk mitigation performance (e.g., traditional benefit of flood risk management), co-benefits, financial costs (life cycle cost analysis), and environmental costs (life cycle assessment). The framework takes current benefit cost analysis practice for both infrastructure types into account, is informed by existing life cycle evaluation methods and tools and is responsive to the unique needs and characteristics of natural infrastructure. Components of this framework have been advanced elsewhere, including in business product management, asset management, building code development, environmental certifications, ecosystem goods and services accounting, and others, but are generally not developed for natural infrastructure. Our proposed framework provides a roadmap for development of supporting resources to conduct life cycle evaluation for natural infrastructure. Systematically grasping the temporal flow of costs and benefits of natural infrastructure, in comparison to conventional flood risk management projects, will be important as societies address vast infrastructure needs in the face of climate change.

Models can be powerful tools to help scientists, policymakers, and practitioners forecast vegetation dynamics and inform management decisions in a variety of ecosystems. In coastal environments, vegetation moderates physical and hydrodynamic processes that conversely affect vegetation dynamics. Coastal management and the implementation of nature-based solutions in the coastal environment requires models that can predict vegetation dynamics that are driven by ecological processes as well as physical processes (e.g., storms, sea level rise). To determine models that are capable of simulating biomass dynamics and assess their ability to make predictions within the context of climate change and environmental management, we reviewed coastal dynamic vegetation simulation models across the following coastal zone habitats: tidal wetlands (salt marsh, mangroves, and freshwater wetlands), seagrass beds, coastal forests (maritime and floodplain forests), and dune habitats. Fifty-four models met the review criteria and were examined to assess their ability to simulate relevant ecological processes and the spatiotemporal scales at which they are applied. These models included a variety of exogenous and endogenous processes and integrate complex ecogeomorphological feedbacks affecting plant and soil community, hydrodynamic, and sediment transport dynamics. Most models reviewed utilized implicit approaches to predicting vegetation biomass and simulated a limited number of processes based on the principal drivers of habitat of interest. Key gaps identified were the exclusion of below-ground biomass dynamics, limited inclusion of processes such as competition, facilitation, and succession, and the inability to simulate management actions. Future models should seek to move towards process-based approaches where appropriate to enable their application to different systems and facilitate their use under novel environmental conditions.

Understanding the drivers of distribution and assemblage composition of aquatic organisms is an important aspect of management and conservation, especially in freshwater systems that are inordinately facing increasing anthropogenic pressures and decreasing biodiversity. For stream organisms, habitat conditions during high flows may be impossible to measure in the field, but can be an important factor for their distribution, especially for less mobile organisms like freshwater mussels. Hence, the objective of this study was to use a two dimensional HEC-RAS model to simulate hydraulic conditions during high and baseline flows (flows approx. 10-600 x and 0.7 x median daily flows respectively) in a 20 km segment in the San Saba River, Texas in combination with existing mussel survey data from 200 sites (collected every 100m) to 1) examine whether hydraulic conditions differed between areas of increased mussel richness and diversity (referred to as hotspots) and other sites, and 2) understand how well site occupancy and species abundance could be explained by hydraulic conditions occurring under different flow conditions. The results showed that richness and diversity hotspots occurred in deeper areas with lower shear stress, stream power, and Froude number during both high and low flows. Occupancy could be predicted with 67-79% accuracy at the site scale and 60-70% accuracy at the mesohabitat scale (∼20 to 1200 m long). In addition, hydraulic conditions across flow scenarios explained up to 55% of variation in species abundances, but predictions were less successful for species often observed to occupy micro-scale flow refuges such as bedrock crevices. The results indicate that pools may serve as important refuge for all species during both high and low flow events, which may be relatively unique to bedrock-dominated systems. Understanding hydraulic conditions that occur at extreme flows such as these is important given that the frequency and magnitude of such events are increasing due to climate change.

The US Army Corps of Engineers, in the responsibility of maintaining navigational infrastructure, has a unique opportunity to improve coastal wetland resiliency and conserve coastal natural infrastructure through the beneficial use of dredged material for wetland restoration. Opportunities are widespread, and tools such as biophysical models can aid coastal managers in assessing habitat vulnerability and planning restoration. In this study, the Marsh Equilibrium Model was utilized in concert with observed data to predict future conditions and evaluate potential effects of beneficial use of dredged material to restore marshes in Mobile Harbor, Alabama. A range of site conditions and two restoration strategies were considered, and the subsequent impact to dredged material management area volumes evaluated. Results showed that wetland restoration via the thin-layer placement of dredged material can restore marsh elevation to combat sea level rise and conserve fill capacity at dredged material management areas. This approach is demonstrated for adoption nationwide by coastal managers.

Background Shallow, tropical coral reefs face compounding threats from habitat degradation due to coastal development and pollution, impacts from storms and sea-level rise, and pulse disturbances like blast fishing, mining, dredging, and ship groundings that reduce coral reefs’ height and variability. One approach toward restoring coral reef structure from these threats is deploying built structures. Built structures range from engineered modules and repurposed materials to underwater sculptures and intentionally placed natural rocks. Restoration practitioners and coastal managers increasingly consider incorporating built structures, including nature-based solutions, into coral reef-related applications. Yet, synthesized evidence on the ecological and physical performance of built structure interventions across a variety of contexts (e.g., restoration, coastal protection, mitigation, tourism) is not readily available to guide decisions. To help inform management decisions, here we aim to document the global evidence base on the ecological and physical performance of built structures in shallow (≤ 30 m) tropical (35° N to 35° S latitude) coral ecosystems. The collated evidence base on use cases and associated ecological and physical outcomes of built structure interventions can help inform future consideration of built structures in reef restoration design, siting, and implementation. Method To discover evidence on the performance of built structures in coral reef-related applications, such as restoration, mitigation, and coastal protection, primary literature will be searched across indexing platforms, bibliographic databases, open discovery citation indexes, a web-based search engine, a novel literature discovery tool, and organizational websites. The geographic scope of the search is global, and there is no limitation to temporal scope. Primary literature will be screened first at the level of title and abstract and then at the full text level against defined eligibility criteria for the population, intervention, study type, and outcomes of interest. Metadata will be extracted from studies that pass both screening levels. The resulting data will be analyzed to determine the distribution and abundance of evidence. Results will be made publicly available and reported in a systematic map that includes a narrative description, identifies evidence clusters and gaps, and outlines future research directions on the use of built structures in coral reef-related applications.

Vegetation plays a crucial role in coastal dune building. Species-specific plant characteristics can modulate sediment transport and dune shape, but this factor is absent in most dune building numerical models. Here, we develop a new approach to implement species-specific vegetation characteristics into a process-based aeolian sediment transport model. Using a three-step approach, we incorporated the morphological differences of three dune grass species dominant in the US Pacific Northwest coast (European beachgrass Ammophila arenaria, American beachgrass A. breviligulata, and American dune grass Leymus mollis) into the model AeoLiS. First, we projected the tiller frontal area of each grass species onto a high resolution grid and then re-scaled the grid to account for the associated vegetation cover for each species. Next, we calibrated the bed shear stress in the numerical model to replicate the actual sand capture efficiency of each species, as measured in a previously published wind tunnel experiment. Simulations were then performed to model sand bedform development within the grass canopies with the same shoot densities for all species and with more realistic average field densities. The species-specific model shows a significant improvement over the standard model by (a) accurately simulating the sand capture efficiency from the wind tunnel experiment for the grass species and (b) simulating bedform morphology representative of each species' characteristic bedform morphology using realistic field vegetation density. This novel approach to dune modeling will improve spatial and temporal predictions of dune morphologic development and coastal vulnerability under local vegetation conditions and variations in sand delivery.

AbstractVegetation shifts can directly alter habitat dynamics and indirectly impact habitat stability relative to disturbance response. Barrier island dune habitats exhibit spatiotemporally dynamic topography that is affected by vegetation. However, vegetation distribution data can be rare and vegetation persistence is largely unknown such that species turnover over in communities can occur unnoticed. This is true despite concerns and documented cases of woody encroachment related to climate change in these ecogeomorphic habitats where physical stability to resist storm erosion varies with vegetation distribution and density. In 1956 and 1957, the vegetation of Island Beach State Park, NJ, was mapped as a permanent record for subsequent ecological study. In June 2020, we remapped the vegetation of 5.4 of 17 km north to south, seaward of the thicket community boundary. We maintained the same classification system as the historic record, physically mapping vegetation patches via GPS. We quantified changes in thicket, heather, and grass community distribution between the two time periods. Habitat persistence and conversion varied in the 63 years. Heath communities saw 80%–97% habitat loss in conversion to woody thicket. Conversely, thicket community distribution drastically increased, replacing heath where it was previously prevalent. This represents the first known documented instances of woody encroachment for Morella pensylvanica. When they did not expand, thicket communities receded landward or underwent turnover to an invasive species. Woody species of interest for dune stabilization occupied areas of similar habitat characteristics. Dune vegetation distribution persistence from 1957 to 2020 was relatively consistent and stable with the exception of heath habitat conversion. Barrier island stability is directly related to vegetation stability such that understanding where community shifts might occur over time can aid in managing and modeling efforts surrounding these dynamic ecogeomorphic habitats.

Coastal communities are highly vulnerable to climate-change associated flood hazards. While hard-engineering solutions (i.e., gray infrastructure) have been widely used to address hazards posed by climate change, demand for natural and nature-based features (NNBFs) as flood risk management alternatives has grown more recently. However, life-cycle analysis frameworks used in traditional planning processes limit comparisons between gray infrastructure and NNBFs by failing to account for non-economic costs and benefits, such as environmental impacts or co-benefits. This study proposes the use of an expanded life-cycle analysis framework that better accounts for traditionally unaccounted benefits and costs. We apply the framework to assess the life-cycle needs of a gray infrastructure project alternative and those of a NNBF alternative to demonstrate how flood risk management alternatives can be compared more effectively and equitably. We leverage dredging and placement cost, post-placement monitoring, and modeling data from the Swan Island Restoration Project, which utilized sediment dredged from nearby navigation channels to restore a highly erosive island in the Maryland portion of the Chesapeake Bay, to describe the application of a life-cycle analysis framework.

This technical note (TN) will outline a framework to identify beneficial and cost-effective coastal beneficial use of dredged sediment (BUDS) projects. Creation of a BUDS framework that can be applied at scale will promote sustainable BUDS practices, facilitating the delivery of flood risk management, social, and environmental benefits while still fulfilling the US Army Corps of Engineers (USACE) navigation mission. This proactive forecasting approach uses multi-criteria decision analysis (MCDA) and optimization tools to balance tradeoffs between navigation dredging and BUDS goals over project-scale timespans. The proposed framework utilizes available tools to quantify ecological system evolution and current and future dredging needs to develop a systems-level approach to BUDS. Required data include current and future information on (1) existing and planned natural and created aquatic ecological systems, which may include natural and nature-based features (NNBFs), (2) dredging requirements and costs, and (3) aquatic system physical and environmental data.

Advancing social equity has been implicitly and explicitly central to water resources policy for decades. Yet, equity remains largely outside of standard water resources planning and management practices. Inclusion of equity within water resources infrastructure is inhibited by barriers including an incomplete conceptual understanding of equity, a perceived lack of quantitative and qualitative equity metrics, unclear connections between equity and standard project planning frameworks, and the absence of concrete examples. To facilitate greater practical inclusion of social equity in water resources practices, we describe equity relative to dimensions of distribution, procedure, and recognition and identify metrics associated with each. We then map these dimensions of equity onto different stages of a water resources project life cycle. We discuss how inequities are often perpetuated by current approaches and highlight case studies that promote one or more of the facets of equity. Rather than providing a prescriptive solution to “achieve” equity within water resources practices, we emphasize the need for contextualized approaches that include pragmatic steps toward more equitable practices and outcomes.

Natural and nature-based features (NNBF) have been used for more than 100 years as coastal protection infrastructure (e.g., beach nourishment projects). The application of NNBF has grown steadily in recent years with the goal of realizing both coastal engineering and environment and social co-benefits through projects that have the potential to adapt to the changing climate. Technical advancements in support of NNBF are increasingly the subject of peer-reviewed literature, and guidance has been published by numerous organizations to inform technical practice for specific types of nature-based solutions. The International Guidelines on Natural and Nature-Based Features for Flood Risk Management was recently published to provide a comprehensive guide that draws directly on the growing body of knowledge and practitioner experience from around the world to inform the process of conceptualizing, planning, designing, engineering, and operating NNBF. These Guidelines focus on the role of nature-based solutions and natural infrastructure (beaches, dunes, wetlands and plant systems, islands, reefs) as a part of coastal and riverine flood risk management. In addition to describing each of the NNBF types, their use, design, implementation, and maintenance, the guidelines describe general principles for employing NNBF, stakeholder engagement, monitoring, costs and benefits, and adaptive management. An overall systems approach is taken to planning and implementation of NNBF. The guidelines were developed to support decision-makers, project managers, and practitioners in conceptualizing, planning, designing, engineering, implementing, and maintaining sustainable systems for nature-based flood risk management. This paper summarizes key concepts and highlights challenges and areas of future research.

In ecogeomorphic systems, such as beach-dune habitats, complex couplings exist between geomorphology and ecology. Abiotic conditions influence vegetation growth and distribution while vegetation imposes a geomorphic feedback, impacting topography. Communities affect storm response by impacting pre-storm state, post-storm recovery, and landscape evolution. Despite their importance, beach-dune and other ecogeomorphic land-sea sys-tems are deteriorating with increased anthropogenic modification and amplified natural disaster impact linked to climate change. A structured approach is needed to develop a more comprehensive understanding of coastal vegetation community interactions with the environment as these interactions underpin topographic change, strom response, and restoration and management efforts. Toward this goal, a spatially explicit process-based grid model, the DOONIES Model, encompassing biological, physiological, and geomorphological drivers of land-scape change is presented. DOONIES simulates critical biotic and abiotic processes of vegetation growth, abun-dance, and spatial distribution dynamics impacting topography and storm response. Biological processes and ecogeomorphic responses are tailored to generalizable dune functional-communities with species-specific repre-sentatives. Estimates of the balance between photosynthesis and respiration dictate plant growth and morphol-ogy spatiotemporally which in turn impact sediment erosion and deposition. Relative sensitivity analyses indicate that the model is fundamentally driven by the photosynthesis formulation, where parameters such as maximum daily photosynthesis (grams of carbohydrate per day) and light intensity impact vegetation growth. These in turn, indirectly impact topographic change in modeled ecogeomorphic links. DOONIES is standalone and with a biological focus making it unique compared to more physical morphodynamic and hydrodynamic models with which this model is designed to couple. The model was evaluated by comparing simulation topog-raphy to actual across 6 years at Island Beach State Park, NJ while modeling Hurricane Sandy and daily wind con-ditions driving sediment input and output events. The predicted results were within the measurement error for the elevation datasets that the simulations were based on. This new model affords dynamic predictions of the re-sponse of naturally occurring and planted dune vegetation communities to typical abiotic conditions, as a tool for supporting and exploring restoration decisions.Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).

Thin layer placement (TLP) is the purposeful placement of thin layers of sediment in an environmentally acceptable manner to achieve a target elevation or thickness. TLP is used for a variety of purposes, such as sediment management, beneficial use of dredged material (DM), and ecological enhancement. The term “thin” is used to distinguish TLP from other methods of sediment placement in which sediments are applied in layers on the order of several meters thick. In this paper, DM disposal refers to the deposition of sediment in a location and manner where no beneficial use is attained; with DM placement the sediment is used to benefit society and the environment. The application of thin layers of sediment has advantages over more traditional, thicker sediment applications in environments where these thicker layers pose potential challenges to natural resources, infrastructure, navigation, or other assets. Although TLP projects are most often conducted in wetlands, there are open-water applications as well. But because TLP is relatively early in its development, there is a dearth of design and construction information and guidance available to practitioners. This paper provides a high-level summary of pending national TLP guidance being developed by the authors on behalf of the U.S. Army Corps of Engineers’ Engineer Research and Development Center (USACE ERDC).

The beneficial use of dredged material (BUDM) for wetland restoration improves coastal wetland resilience and conserves coastal natural infrastructure. Tools, such as biophysical models help coastal managers to assess habitat vulnerability and plan restoration. In this study, the Marsh Equilibrium Model (MEM) will be utilized combined with observed data to predict future conditions and evaluate potential marsh restoration via the BUDM in Mobile Bay, Alabama. A range of site conditions and restoration strategies will be considered and the impacts on dredged material management area (DMMA) volumes will be evaluated. Wetland restoration via thin-layer placement (TLP) of dredged material (DM) restores marsh elevation to combat sea level rise (SLR) and conserves fill capacity in DMMAs. A simplified mapping approach to assess this type of restoration will be demonstrated using wetland area and DM sources to determine the coastal United States wetland area to which it could be further applied. The mapping exercise revealed that 6,240 km2 of US wetlands were suitable for restoration and sediment resources exist to conduct this type of restoration from navigational dredging. The further development of a spatial application of the MEM is needed to provide an operational tool for managers and refine these restoration estimates.

This special report discusses the outcomes of a September 2019 workshop intended to identify barriers to the consideration and implementation of natural and nature-based features (NNBF) in US Army Corps of Engineers (USACE) civil works projects. A total of 23 participants representing seven USACE districts, the US Army Engineer Research and Development Center (ERDC), and the University of California–Santa Cruz met at USACE’s South Atlantic Division Headquarters in Atlanta, Georgia, to discuss how to facilitate the implementation of NNBF into USACE project planning for wetlands and reefs using six categories: (1) site characterization, (2) engineering and design analysis, (3) life-cycle analysis, (4) economic analysis, (5) construction analysis, (6) and operation and maintenance (and monitoring). The workshop identified seven future directions in wetland and reef NNBF research and development: • Synthesize existing literature and analysis of existing projects to better define failure modes. • Determine trigger points that lead to loss of feature function. • Identify performance factors with respect to coastal storm risk management (CSRM) performance as well as ecological performance. • Focus additional research into cobenefits of NNBF. • Quantify the economic life-cycle costs of a project. • Improve technology transfer with regards to NNBF research and topics.

This report assesses potential impacts to aquatic resources resulting from proposed navigation channel expansion activities within Mobile Bay, Alabama.This work was conducted for the U.S. Army Corps of Engineers (USACE) Mobile District, to support development of a supplemental Environmental Impact Statement.Changes in water quality and hydrodynamics were evaluated for potential impacts to benthic macroinvertebrates, wetlands, submerged aquatic vegetation, oysters, and fish.The assessment includes extensive characterization of baseline conditions, evaluation of estimated post-project conditions related to aquatic resource habitat (e.g., changes in salinity, dissolved oxygen).An analysis of potential impacts related to a 0.5-m sea level rise (SLR) scenario were also evaluated.Results suggest that no substantial impacts in aquatic resources within the study area are anticipated due to project implementation, as the area of greatest potential changes to environmental conditions are already adapted to natural shifts in salinity (and other factors), and to conditions resulting from the existing navigation channel.Although SLR has the potential to alter aquatic resource habitats with Mobile Bay, additional impacts related to project implementation remain negligible under the 0.5-m SLR scenario.

Acid sulfate soils naturally occur in many coastal regions.However, the oxidation of acid sulfate soils can decrease soil pH to <4.0, affecting vegetation and aquatic organisms.Acid sulfate soil oxidation typically occurs where anaerobic sediments or soils were exposed to aerobic conditions (for example, extended drought, artificial drainage, or dredged material placement in upland areas).Recently, field observations documented the formation of acid sulfate materials at multiple degraded marsh restoration locations (Rhode Island, New Jersey, California) following intentional dredged sediment placement into wetland environments designed to increase marsh elevation.Unlike previous studies of acid sulfate soils, the in situ dredged material did not contain acid sulfate-bearing materials at the time of placement; instead, the interaction between the marsh substrate and the overlying dredged material appears to have caused the formation of acid sulfate soils.These findings highlight the need for additional studies of acid sulfate soil formation and fate-especially within a marsh restoration context.In response, this report provides a review of literature related to acid sulfate soils, discusses preliminary data collected to evaluate acid sulfate material formation following marsh restoration, and identifies knowledge gaps requiring additional research and technical guidance.

Salmonid species are critically important ecologically, socially, and economically for North American coastal regions. Alterations to the structure (e.g., channelization) and function (e.g., sediment transport) of estuaries, rivers, and streams have greatly impacted these species, many are now listed as federally threatened or endangered. As part of environmental compliance procedures and policy, the U.S. Army Corps of Engineers (USACE) is required to assess the impacts and/or benefits of proposed water resource projects (e.g., levee maintenance, ecosystem restoration, etc.) to the environment. The USACE is required to predict and quantify environmental benefits using models to justify federal investment in ecosystem restoration projects. The purpose of this effort is to develop a general model or model framework that can be used during the USACE planning process that will serve as a unified standard Salmonid model. The primary purpose of the model will be to project future environmental benefits that will result from proposed restoration measures. Additionally, the model needs to be sensitive to different combinations of restoration measures in order to assist the USCAE in the planning and decision making process. This report presents the results of the first phase of model development using the mediated model development process.