Key Points Coastal risk reduction can be achieved through a variety of approaches, including natural or nature-based features (e.g., wetlands and dunes), nonstructural interventions (e.g., policies, building codes and emergency response such as early warning and evacuation plans), and structural interventions (e.g., seawalls and breakwaters).
Natural and nature-based features can attenuate waves and provide other ecosystem services (e.g., habitat, nesting grounds for fisheries). However, they also respond dynamically to processes such as storms, both negatively and positively, with temporary or permanent consequences. Nonstructural measures are most often under the jurisdiction of state and local governments (and individuals) to develop, implement, and regulate, and they cannot be imposed by the Federal government. Perhaps more well known are the structural measures that reduce coastal risks by decreasing shoreline erosion, wave damage, and flooding.
The USACE planning approach supports an integrated strategy for reducing coastal risks and increasing human and ecosystem community resilience through a combination of the full array of measures: natural, nature-based, nonstructural, and structural. This approach considers the engineering attributes of the component features and the dependencies and interactions among these features over both the short and long term.
Knowledge about the performance of natural, nature-based, nonstructural, and structural features varies, as do the methods used to calculate and measure performance. Factors include the specified objectives, the threats under consideration (e.g., the particular range or frequency of coastal storms), and the technical information that is available for describing the relevant processes and functions. Applying a systems approach to coastal risk reduction necessitates a rigorous scientific and engineering analysis of the performance of all system components as part of planning, designing, constructing, operating, maintaining, and adaptively managing the features comprising the system.
Federal investment in features intended to provide coastal risk reduction and resiliency should rest on solid evidence about performance. Focused research is needed to reduce the uncertainties involved in evaluating and quantifying the value and performance of natural and nature-based measures for shoreline erosion and coastal risk reduction. Federal investments supporting erosion mitigation and coastal risk reduction and resilience could benefit from more consistent integration of natural and nature-based infrastructure.
Incorporating social sciences along with physical sciences and engineering can help improve understanding of measures that encompass social (technological, institutional, and behavioral) responses and legal issues. This would help to better inform investments in coastal systems and result in longer-term benefits for coastal risk reduction and an array of societal needs.
Key Points: New York City’s coastal zone encompasses the extensive wetlands of Jamaica Bay and Long Island Sound, dense commercial centers and industrial areas, beachfront residential communities, and myriad other neighborhoods. Much of the literature on coastal resilience in the United States, however, is focused primarily on relatively low-density communities. This study aims to explore the range of coastal management and protection options that are suited to urban areas with large existing populations in flood zones, limited space, and shorelines that have been altered and often hardened in a variety of ways. Given the diversity of geography and uses within urban areas, there is no one size fits all approach to climate resilience, nor is there one “silver bullet” solution to managing risks. Each stretch of the waterfront faces specific types and levels of risk and presents different opportunities and constraints.
Each strategy carries with it costs and benefits, which should be broadly defined. Potential costs include financial costs, both to construct and maintain new pieces of infrastructure, as well as indirect costs, such as environmental degradation, impacts on neighborhood vitality, economic activity and tax revenues, or the quality of public space and urban design. The benefit of a strategy can be measured in terms of risk reduction, as well as the potential co-benefits associated with it, such as environmental improvements, economic development, and the improvement of the city’s public realm.
To understand the range and nature of hazards and vulnerabilities throughout the city, this study set out to develop a set of coastal area typologies representative of the range of conditions found in New York City that would reflect the metropolitan region as well. The 520 miles of shoreline within New York City were analyzed through two distinct lenses: coastal geomorphology, or the physical landforms that relate to coastal processes, and the built environment, or the uses and their density that are found throughout the coastal zone. The coastal geomorphology is a composite of the glacial landforms, slope, elevation, shoreline condition and wave exposure which together depict the exposure of a given reach to the coastal hazards identified: event-based storm surge, wave forces, and erosion, and gradual flooding and erosion due to sea level rise. Land uses and density, including the types of uses, functions, infrastructure, and populations, are a measure of an area’s vulnerability to the coastal hazards that are present. This gives an indication of the magnitude of the consequences should the area be impacted by a coastal storm or gradual sea level rise.
This analysis identified nine types of geomorphology and eight types of land use. The geomorphology types vary in terms of the degree and nature of exposure to different coastal hazards, for instance whether or not there are significant wave forces and how high potential flooding is likely to be. The land use types range from open space, to lower-density residential areas, to medium density areas with a mix of uses, to high density commercial areas. Nine combinations of land use and geomorphology that were commonly found in New York City and which represented a range of conditions were chosen. These resulting “coastal area typologies” are presented to understand the nature and extent of risk from coastal hazards and what sort of strategies would be most suitable and effective.
The likely impacts of an alternative on either promoting or hindering the ability of natural systems to perform ecological services and provide biodiversity can be evaluated through a mix of quantitative and qualitative analysis. Equity can be considered by identifying disparities in how the benefits and external costs of an alternative are shared among population groups. Impacts on the public realm and urban design can be examined through a mix of qualitative information (such as a rendering) and quantitative data (such as estimates on the amount of public space lost). Other elements, such as consistency with local plans require qualitative analysis. It should be particularly noted when a project is able to further a local planning objective, such a providing access to the waterfront, improving drainage in a neighborhood or providing habitat restoration opportunities.
In addition to noting the costs and benefits of various alternatives, it is also necessary to look at who pays the costs and who benefits. In instances that involve the construction of new, significant pieces of infrastructure, the benefits are substantially to private entities while many of the costs are borne by the public sector (which is funded in large part through taxes). Financing mechanisms that balance the costs and benefits to the public and private entities should be considered.
Because projections of future risk are uncertain, the benefits of taking mitigating actions are also uncertain. Therefore alternatives that are the easiest to make actionable are those that have few costs and address significant near-term risks, or so-called “no regrets” strategies. Other alternatives are more likely to prove cost-beneficial are those that are robust and work for a wide range of possible future outcomes, or those that provide additional benefits that aren’t as uncertain. Understanding the time it will take to implement a given alternative and the ways in which cost-effectiveness of an alternative changes over time are important to making these decisions. Keeping a broad view of costs and benefits is important throughout.
Reference #3: NACCS Citation:
Title: North Atlantic Coast Comprehensive Study: Resilient Adaptation to Increasing Risk MAIN REPORT
Key Points: Changing sea levels represent an inexorable process causing numerous, significant water resource problems such as: increased, widespread flooding along the coast; changes in salinity gradients in estuarine areas that impact ecosystems; increased inundation at high tide; decreased capacity for stormwater drainage; and declining reliability of critical infrastructure services such as transportation, power, and communications. Addressing these problems requires a paradigm shift in how we work, live, travel, and play in a sustainable manner as the extent of the area at very high risk of coastal storm damage expands.
The North Atlantic Coast Comprehensive Study (NACCS) provides a step-by-step approach, with advancements in the state of the science and tools to conduct three levels of analysis. Tier 1 is a regional scale analysis, Tier 2 would be conducted at a State or watershed, and Tier 3 would be a local-scale analysis that incorporates benefit-cost evaluations of coastal storm risk management plans.
The current approach to coastal storm risk management includes a myriad of individual projects to address independent problems. The dynamics, complexity, and risks germane to coastal systems cannot be adequately addressed by incrementally building a patchwork of solutions. A systems approach to coastal storm risk management is a cornerstone of the NOAA and USACE Infrastructure Systems Rebuilding Principles.
Site-specific solutions can produce benefits and consequences to the region, or system, and vice versa. The NACCS presents a range of solutions and an evaluation of the potential reduction in risk compared to the relative cost of the strategies and measures. The Framework identifies the strategies and measures that provide the greatest risk reduction for the lowest cost. Understanding the full array of measures and the relative cost of pursuing certain levels of risk reduction is critical. This transparent and transferable process does not prohibit consideration of additional measures and relative costs. Combinations of risk management measures, including floodplain and evacuation planning, managed retreat, buyouts, NNBF, and structural solutions are some of the ways to adapt to future sea level and climate change.
Holistically evaluating and comparing solutions based on future visioning, short-term and long-term costs and financing strategies, environmental and cultural resources, the economy, and much more will ensure that investments in our communities and along our coastline are strategic and forward-thinking.
In the face of highly uncertain outcomes associated with climate change, coastal storm risk management decisions based solely on a single most probable or likely outcome can lead to inaction, poor project performance or maladaptation. This uncertain future suggests a transition to an “explore-then-test” decision context in which multiple scenarios are evaluated and coastal storm risk management measures are judged by their adaptability and function across the full range of future risks. USACE recommends a tiered approach to the assessment of sea level change on project alternatives and project performance using three scenarios of sea level change.
Accepting certain levels of risk, making cultural changes, planning for the future, creating public-private partnerships and incentive programs, and implementing measures and combinations of measures to address coastal storm risk management of risk areas will be driven by regional coordination between Federal, State, local, and tribal officials. Regional coordination should occur through an interagency stakeholder group, chartered to periodically review, evaluate, and coordinate development and implementation of coastal storm risk management features and programs. Close coordination by these groups will help ensure buy-in by all affected constituents and assist communities in becoming more resilient to future storm events.
Reference #4: Resilience – Royal Society Citation:
Title: Resilience to Extreme Weather
Authors: Paul Nurse, President of the Royal Society
Organization: The Royal Society, Science Policy Centre
Key Points: While there is a lot of information available about different options designed to reduce the impact of extreme events and prevent disasters, much of it is not directly comparable. To enable some broad comparisons, the plots below, including the choice of option, have been developed based on a combination of relevant research literature and expert scores and opinion… The plots compare the effectiveness of each option (encompassing both the magnitude of the event against which the intervention can be effective and the spatial scale over which it is effective) versus the affordability (based on a combination of both the initial and long-term (to 2050) costs of the intervention).
They also show an assessment of the strength of the evidence regarding the cost-effectiveness of each option and an assessment of the additional consequences of that intervention on some key factors beyond the impact on the hazard being considered. These factors are: access to food, access to water, access to livelihoods, biodiversity, climate change mitigation and protection against other hazards. Scores were sought as to whether the impact of the intervention would be positive, neutral or negative on each factor.
The purpose of this analysis is to draw out broad recommendations regarding what to consider when making plans to protect people from extreme weather. The plots are indicative and cannot be used to decide between individual options. This is because the plots consider individual events in isolation; a single score is used to assess options which vary depending upon the context, or can be implemented in a variety of ways; possible impacts of poor implementation are not considered; all possible options are not included and nor are all possible additional consequences. Decisions about which options to use need to take into account the specific context as well as the affordability and effectiveness.
The drought plot has a different pattern from the other three, with a more mixed picture of the affordability and effectiveness of options – some engineering options being less effective than some ecosystem-based and hybrid ones. Drought is different from many other hazards because it involves a wide range of processes and operates over a long period of time. The problem is one of a scarce resource, so engineering options only help where they are accessing water that is otherwise unavailable (eg wells) or unuseable (eg waste water recycling). Catching and making best use of what rain does fall is a key response. Techniques that do this, such as the soil and water conservation options, tend to be smallscale and ecosystem-based or hybrid.
These plots suggest that:
• Engineering options are often the most effective in reducing the impact of the hazard. However, they generally have low affordability and few additional benefits. The evidence base for these options is strong.
• Ecosystem-based options are the most affordable and have positive additional consequences, but are often not as effective as other options at reducing the impact of the hazard. The evidence-base to support these options tends to be weaker so there is uncertainty regarding their effectiveness.
• Hybrid options tend to be in the middle in terms of effectiveness and affordability but often have positive additional consequences. The strength of evidence to support these options varies but is generally stronger than that for ecosystem-based options.
There is strong evidence for engineering options that are long established and have an easily measureable impact upon the hazard, such as dykes, dams, air conditioning and wells. In contrast, the role of ecosystems in reducing the impact of extreme weather has only relatively recently been appreciated and begun to be measured; as a result the evidence for these options is weaker. Some hybrid options are supported by stronger evidence than the ecosystem-based ones because of the well-evidenced engineering components they include.
Much work is currently being done to test ecosystem-based and hybrid approaches. However, data collection and scientific monitoring is not always planned when practical projects are designed, and there are currently no standards to ensure that monitoring will be effective and allow comparison with other options. Much evaluation is anecdotal, and has not been peer-reviewed and tends to focus on success.
Different types of extreme weather may require different options and interventions of different scales. There is also variation in the scale at which options operate most effectively and in the extent to which options can be scaled up. There is some evidence to suggest that ecosystem-based options are more effective against events that are smaller, slower onset and/or more extensive. The results above support this: ecosystem-based approaches rarely score highest for effectiveness, which according to the guidance that was given to experts should be given to options effective ‘against extreme events – 1 in 200 years’. However, there is some emerging evidence which contradicts this, at least for certain hazards (storm surges) and suggests that some ecosystem-based techniques may be effective against even the most extreme events.
The variation in the effectiveness and affordability of options suggests that a range of options should be used, each of which can be effective against different scales and intensities of extreme weather. This range, or ‘portfolio’, should include options not covered in the plots above, such as social and behavioural options, which can be effective against a range of hazards. In addition to the general rule that deploying a greater array of resilience options leads to a greater array of benefits, some options necessarily overlap with and can be prerequisites for others. Social approaches are often vital to building resilience and frequently increase the effectiveness of other options. For instance, many of the drought options work better where local people have recognised rights to manage land and water – both on an individual family basis and as a collective group. If the interventions are mutually supportive, the combined impact can be even greater.
Offering protection against multiple hazards is an important additional benefit given that hazards seldom occur in isolation but can take place simultaneously or in a cascade. All the categories of intervention score positively overall for this factor. Engineering approaches, which are usually designed to reduce the impact of a specific hazard, achieve the lowest overall score. Ecosystem-based approaches, some of which are less hazard specific – for example, coastal forests can offer protection against coastal flooding, inland flooding, high winds, and high temperatures – score more highly for protection against multiple hazards.
The results of the comparative analysis suggest that ecosystem-based options can be effective in reducing the impact of the events considered. Although quantitative comparison of options is not possible, there are numerous studies demonstrating the effectiveness of a variety of ecosystem-based approaches.
Reference #5: Design manual from the US Army Corps of Engineers from 1995. You can see it shows lots of figures and tables and checklists for designing seawalls, revetments and bulkheads. Now, twenty years later, the USACE has put out new recommendations at the website: http://www.nad.usace.army.mil/Portals/40/docs/NACCS/NNBF%20FINAL.pdf (report is over 400 pages long and files to too big to emails). Note that this new report includes considerations for nature based coastal protection. However, this is a general framework for consideration and discussion, and not a prescriptive design manual. This is both interesting and challenging for some engineers, as we are used to working with the more traditional design manual approach. http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-2-1614.pdf