Foreseeing Coastal Change To Strategically Guide Adaptation ^ CLIMATE READY ESTUARIES v>Em vvEPA United States Environmental Protection Agency Office of Water 840R25001 January 2025 ------- FORESEEING COASTAL CHANGE COASTAL EFFECTS Change is coming to America's coasts. Sea level rise, warmer temperature, ocean acidification, and coastal storms are further disturbing already stressed interlocking social, economic and environmental systems. We have known for decades that storms would be more damaging. Yet our coastal management conversations need greater awareness that change is coming from more directions. Most of the public discourse about coasts and resiliency focuses on storms and disasters, walls and barriers, and resistance or retreat. However, change can derive from many paths. Comparatively little attention goes to the staggering ecological losses of tidal wetlands. When wetlands are discussed, the focus is usually on the hope that they protect private property from damage. Even less public attention is paid to the stresses and impacts that come from warming water and ocean acidification. These will compound the effects of eutrophication, hypoxia, dead zones and harmful algal blooms that continue to resist solutions. Sea level rise will exacerbate coastal storms but will also produce chronic impacts, such as high tide flooding and groundwater salinization. Further, coastal change can come from how communities gird for threats, how residents respond to their shifting personal situations, or how the natural resource, water utility and energy sectors mitigate or exploit new conditions. This strategic foresight project begins a conversation about emerging risks and opportunities. It is intended to guide coastal managers to anticipate a wider range of future conditions in order to accelerate preparation and adaptation. It furthers the longstanding Climate Ready Estuaries program goals of assessing vulnerabilities; developing and implementing adaptation strategies; and engaging and educating stakeholders. The analysis and exposition also support EPA's Office of Water priorities to improve the resilience of America's water infrastructure; protect America's waters; advance the adaptive capacity of the water sector; and raise the awareness of communities and decision makers. STRATEGIC FORESIGHT In ways that may range from unsurprising to unexpected, coastal evolution is impending across the social, economic and environmental spectrum. Strategic foresight is a tool for broadening awareness about what is currently out of mind yet could be just over the horizon. This is a project to scan, identify trends, and guide coastal managers to anticipate the future. It highlights place-based change produced by: climate stressors, adaptation in response to the local impacts of a changing environment, and/or human action in response to global conditions. ------- Although impacts will be numerous and diverse, this project focuses on topics that span Clean Water Act intersections with coastal management. They feature developments related to: point and nonpoint sources of pollution; healthy fish, plants, and wildlife; public uses; and restoring and protecting habitat. Habitat 01. Removing tidal restrictions 02. Resorting to floating wetlands 03. Withstanding seagrass crashes 04. Establishing marsh migration corridors 05. Farming blue carbon Infrastructure 06. Reengineering combined sewer systems 07. Paying for new water infrastructure 08. Generating electricity within estuaries 09. Truncating the tide Water quality 10. Providing refuge from acidification 11. Lowering stream temperature 12. Minding deoxygenation 13. Enduring marine heatwaves Society 14. Turning to floating buildings 15. Losing waterfront access 16. Extending the boating season 17. Turning to artificial intelligence 18. Restoring abandoned sites The scene setting stories present concepts of coastal conditions at mid-century (circa 2050). These short narratives seed a set of two-page assessments that analyze their components and evaluate the storylines. METHODOLOGY While the aim is to bring issues forward to inform policy discussions or stimulate adaptation, at this time no one can say for certain what any place will be like in 2050. This is a look over the horizon, which inherently entails extrapolation and some speculation. The topics were purposely selected to bring attention to less familiar tracks and thus they may have a very small research base. Inherently too, stories of the future describe untestable environmental states. Inferences and judgment are required. It is possible to craft a logical and reasonable reading of a potential future. We know that change is being felt and stressors continue to strengthen. We see trends and movement in the past decade such as: policy research on tidal restrictions, increasing losses of coastal wetlands and the likelihood of even worse future losses, the accumulating tally of "billion dollar storms," more shoreline armoring, and the rise of wind and solar power. What has been missing from the national conversation is awareness of how developments such as these can produce change at the scale of a place. Information about trends, future conditions or cases related to this very diverse set of topics can be synthesized from a range of sources such as peer reviewed literature, reports from governments, industry, non-governmental organizations, trade journals, online maps, news accounts, or other sources. Analysis could proceed by asking questions such as: is it already ------- observed in some places? is it in experiment, planning or pilot stages? does a trend point that way? is it an absent/present phenomenon or does it build in intensity? is it a logical outgrowth of other policies? what do we know from analogous cases? is it contingent on other events? how likely is this to be seen in 2050? what is the timing? These are compact investigations to begin important conversations, they can hardly be comprehensive. Furthermore, different people can draw different conclusions about how U.S. coasts will be in another quarter century: crystal balls are always cloudy. This work aims to generate thoughts about a sustainable future and support strategic planning, and therefore the quality objectives in this project were: 1. All report content can sustain a challenge to its reasonableness. 2. The disseminated information is accurate, reliable, and unbiased. 3. The assessments are useful for coastal management. To be useful a scene setting story and its assessment must have logic, and judgment about likelihood is justified. Decision makers cannot get a bullet-proof prediction about what the whole U.S. shoreline will look like a quarter century from nowthey can have useful impressions which can lead to informed next steps. Within the assessments, the stories are set out in a coastal futures section that assumes they have already been realized at mid-century. An assessment adopts a future viewpoint in how does it look and how did it happen sections, which crisply describe what happened since the 2020s to bring about the mid-century condition. An assessment also includes a how likely is it section that considers the probability of events occurring in that way. Estimated chance Terminology > 9 in 10 ( > 90% ) Very likely >2 in 3 (>67%) Likely ~ 1 in 2 ( ~ 50% ) As likely as not About an even chance < 1 in 3 ( < 33% ) Unlikely < 1 in 10 ( < 10% ) Very unlikely To support policy making and strategic planning, a temporal return to the present period allows consideration of selected opportunities and challenges which are additional factors connected to a story line. Also provided are a few notable policy context and questions that focus on associated management or technical subjects. DECISION SUPPORT The assessments are intended to envision plausible coastal trajectories and support decision making for a sustainable future. Armed with foresight, now is the time to nudge the direction or push for better outcomes. Regardless of whether a future condition is wanted or unwanted, likely or not, agencies and managers can make choices to alter pathways. Desirability Probability = likely Probability = unlikely Wanted How can it be made even likelier? What has to change to bring this on? Unwanted What has to change to keep this off? How can it become even less likely? There is no single answer. There are many vectors. The U.S. shoreline varies considerably. Different situations call for different tools. These assessments are not policy prescriptive and ------- are meant to bring attention to looming topics. However, time is short for policy makers if they want to affect trends and midcentury outcomes. The instruments many environmental managers use to meet their mission generally include: leadership: including setting the agenda, convening stakeholders, assembling partners research: to acquire knowledge, survey needs, produce metrics, test solutions regulation: including rulemaking, guidance, compliance, enforcement financial assistance: including loans, grants, cooperative agreements technical assistance: including methods, tools, program development techniques, training education: including public advisories, information sharing, outreach cleanups: such as at brownfield and Superfund sites emergency response. Twenty-five years does not leave much time to set a direction, develop the tools, implement solutions, and produce satisfactory outcomes. If we are serious about protecting and restoring water quality, increasing resilience: protecting public health: conserving land, water and biodiversity: and spurring economic growththen we must wrestle with the subjects of these strategic foresight assessments. FURTHER READING Science Advisory Board. 1995. Beyond the Horizon: Using Foresight to Protect the Environmental Future. EPA-SAB-EC-95-007. Washington, DC: U.S. Environmental Protection Agency. EPA. 2006. Shaping Our Environmental Future: Foresight in the Office of Research and Development. EPA 600/R-06/150. National Academies of Sciences, Engineering, and Medicine. 2016. Transitioning Toward Sustainability: Advancing the Scientific Foundation: Proceedings of a Workshop. Washington, DC: The National Academies Press. EPA. Unpublished (2016). U.S. EPA Strategic Foresight Pilot Project: Report and Findings of the Strategic Foresight Lookout Panel. Prepared for: Office of the Science Advisor and Office of the Chief Financial Officer. GAO. 2019. Overview of GAO's Enhanced Capabilities to Provide Oversight, Insight, and Foresight: Statement of Dr. Timothy M. Persons, Chief Scientist and Managing Director, Science, Technology Assessment, and Analytics, Testimony Before the Committee on Science, Space, and Technology, Flouse of Representatives. GAO-20-306T. ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Sea level rise squeezes salt marshes against tidal restrictions, threatening long-term wetlands persistence and consequently the social, economic, habitat, and water quality services they provide. Removing tidal restrictions restores natural marsh processes and opens new areas that can support salt marsh habitat. REMOVING TIDAL RESTRICTIONS COASTAL FUTURE HOW DOES IT LOOK? In some salt marshes, natural tidal flow was restricted by transportation and water infrastructure. Tidal restrictions prevented inland marsh migration leading to increasing wetland losses as sea level got higher. Once these impediments were removed, salt marsh ecosystems began migrating into previously blocked spaces and are establishing themselves faster than society could build new marshes an acre at a time. The opening of blocked areas to salt marsh colonization restored habitat for fish and birds and improved tidal flushing. II has been a bright spot in the ongoing losses of marsh habitat from sea level rise. HOW DID IT HAPPEN? Accelerated sea level rise was drowning low elevation salt marshes. However, when suitable conditions existed at higher elevation, the marshes could colonize those areas. Removing tidal restrictions allowed more natural flow and enabled marsh migration into blocked areas. Many places modified their engineering procedures to assess the severity of tidal restrictions and prioritize efforts to reconnect landscapes. Smaller projects often involved retrofits to resize restrictions (e.g., upsizing culverts during routine road maintenance). Larger projects (e.g., dam, dike, levee removal, or roadway elevation) needed extensive analysis and greater public outreach. Restored tidal flow often quickly led to the reestablishment of characteristic species and water quality improvements as stream flow, sediment processes, and vegetation returned to a more natural state. Salt marsh colonization of reconnected upstream areas allowed for the ecosystem type to persist despite other losses to permanent inundation caused by sea level rise. HOW LIKELY IS IT? Sea level rise is already causing marsh loss. As coastal flooding increasingly affects shoreline communities, there is growing interest in using natural systems for hazard mitigation. Given the turn to nature-based solutions, alarming trends for wetland losses, interest from agencies, and establishment of engineering best-practices and design standards, removing tidal restrictions is likely. Considerations such as ecological restoration potential, enhanced fish passage, flood risk, infrastructure life cycles, and magnitude of benefits will affect prioritization. Some coastal places have lower potential for marsh migration due to local constraints or high rates of sea level rise and subsidence. Tidal restrictions are most likely to be removed when restrictive infrastructure (e.g., culverts, dams) fails or otherwise requires significant maintenance, and restoration poses limited flood risk to development. A new bridge over a stream where culverts once blocked passage (NOAA Fisheries). Assessment 0 I -2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES Improving fish passage can overlap with salt marsh restoration as tidal restrictions impede both the movement of water and fish. More saline conditions in newly opened areas can lead to the displacement of valuable freshwater wetland and upland habitat types, which will also need to migrate upward and inland to persist. In some locationswithout other hazard mitigation such as elevating buildings or buyoutschanged tidal flow may increase flooding risks. POLICY CONTEXT AND QUESTIONS Land available for migration within coastal watersheds is limited and there can be social, economic, and environmental conflicts. Tidal restrictions can be assessed and prioritized for upgrade or removal. In addition to guiding removal, best- practices and standards can be updated to avoid introducing new tidal restrictions. Removal can require a significant permitting effort and various approvals. Updating approved methods for cost-benefit analysis to account for ecosystem-scale benefits and avoided risks will be helpful. This scenario connects to sustainability goals for: clean water and sanitation sustainable cities and communities life below water life on land. Potential area available for wetland migration in response to sea level rise in the conterminous United States (Osland, Michael J., Bogdan Chivoiu, Nicholas M. Enwright, Karen M. Thorne, Glenn R. Guntenspergen, James B. Grace, Leah L. Dale et al. "Migration and transformation of coastal wetlands in response to rising seas." Science advances 8, no. 26 (2022): eabo51 74. SELECTED REFERENCES U.S. Environmental Protection Agency. Tidal Restriction Synthesis Review: An Analysis of U.S. Tidal Restrictions and Opportunities for their Avoidance and Removal. EPA-842-R-20001, 2020. Osland, Michael J., Bogdan Chivoiu, Nicholas M. Enwright, Karen M. Thorne, Glenn R. Guntenspergen, James B. Grace, Leah L. Dale el al. "Migration and transformation of coastal wetlands in response to rising seas." Science advances 8, no. 26 (2022): eabo5174. htti3s://doi.ora/10.1126/sciadv.abo5174. U.S. Environmental Protection Agency. An Integrated Framework for Evaluating Wetland and Stream Compensatory Mitigation. EPA-840-B-22008, 2022. New Hampshire Department of Environmental Services. Resilient Tidal Crossings: An Assessment and Prioritization to Address New Hampshire's Tidal Crossing Infrgstructure for Coostgl Resilience. R-WD-19-20, 20 ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Sea level rise drowns salt marshes faster than they can grow and squeezes them against coastal development causing habitat loss. Building and installing large scale systems of floating wetlands can preserve some vital ecological functions and services. RESORTING TO FLOATING WETLANDS COASTAL FUTURE HOW DOES IT LOOK? Salt marshes were being squeezed between rising sea level and development on their landward side. As estuarine marsh acreage rapidly diminished, there was a turn to large scale systems of artificial floating wetlands to maintain some of the ecosystem services that salt marshes provided. While an imperfect substitute for a healthy wetland with rich soil, the floating marshes offered an alternative to the looming environmental impoverishment that would come from total coastal wetland loss. HOW DID IT HAPPEN? By installing large scale systems of floating wetlands to counter losses from sea level rise, shoreline areas capitalized on the ecosystem benefits that these engineered systems provide. Different places designed their wetlands for different priorities, such as providing bird and wildlife habitat, dampening waves, improving water quality, or conserving fisheries. Using buoyant containment, floating wetland systems let wetland plants grow hydroponically where water depth and wave energy allowed. Installations do not rest on bottom habitat and were also located to avoid shading seagrasses. Because of size limitations and limited lifespans of floating wetland systems, many places opted for groups of floating wetlands rather than large singular installations. HOW LIKELY IS IT? Because salt marshes are one of the fastest disappearing ecosystems and they provide significant environmental benefits, it is about an even chance that park and refuge managers and others will turn to floating wetland systems to ensure that these benefits are not entirely lost. There is currently some experience with floating wetlands in controlled freshwater settings for wastewater treatment and nutrient management. They have also been used in small plots, including in tidal areas, for waterscaping. Floating wetlands are not as effective in high wave, high erosion areas because storms can damage or dislodge thee structures and create potential hazards. The likelihood of adopting this strategy will be influenced by site parameters and the particular environmental benefits that are wanted or achievable. 71»rya J n 'J- tr^rSi a Mr- ;.rr iVsvV ''f #r/"iEUh Assessment 02-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES Floating wetlands can serve as public demonstration projects, offering opportunities to educate the public about the ecosystem services that existing intact salt marshes provide and their value for adaptation. Installations can be designed with variable heights to support multiple microhabitats and provide for native flora and fauna. Not all functions and services can be completely restored, and some (such as those coming from rich soil) may not be replicable. Containment can deteriorate and can be damaged by storms. Owners will need to plan for maintenance and replacement. Best practices guides and design standards can be updated as experience is gained. Locational decisions may need to be revisited as sea level rise and coastal change progress. POLICY CONTEXT AND QUESTIONS Concerns with floating wetlands installations may include impacts to aquatic resources, title to submerged lands, or competing uses such as fishing and boating. Most permitting agencies are unfamiliar with floating wetlands as a replacement for some of the functions of the lost salt marshes. Nationwide permits could be considered. This scenario connects to sustainability goals for: clean water and sanitation sustainable cities and communities life below water life on land. Visitors pose for pictures and explore the flora and fauna at the Floating Wetiands by Jurong Lake in Singapore. SELECTED REFERENCES Cicero-Fernandez, D., Exposito-Camargo, J.A., and Pena-Fernandez, M. Efficacy of Juncus maritimus floating treatment saltmarsh as anti-contamination barrier for saltwater aauaculture pollution control. Water Science & Technology 85, 10 (2022): 281 1-2826. Hopkins, Julia el al. The Emerald Tutu: Floating Vegetated Canopies for Coastal Wave Attenuation. Frontiers in Built Environment 8, (2022). Kgrstens, Svenjg et g|. Constructed flooting wetlgnds mgde of naturgl materials as habitats in eutrophicoted coastal lagoons in the Southern Baltic Sea. Journal of Coastal Conservation 25, 44 (2021). Likitswat, Fg et g|. (2023). Designing Ecolooicgl Flooting Wetlgnds to Optimize Ecosystem Services for Urbon Resilience in Tropicol Climgfes: A Review. Future Cities and Environment 9, 1 (2023): 1 -12. ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Estuary water temperatures are rising beyond the optimum levels for Eelgrass. This keystone ecological species is being replaced by Widgeon Grass. Widgeon Grass is an imperfect replacement and is prone to population crashes in years with high rainfall and greater nonpoint source pollution. WITHSTANDING SEAGRASS CRASHES COASTAL FUTURE HOW DOES IT LOOK? As estuary temperatures warmed up, Eelgrass (Zostera marina) disappeared from the southern portions of its range. Eelgrass was an essential habitat and a base of primary production. It stabilized bottom sediment, improved water quality, and had a role in mitigating acidification. The replacing species, Widgeon Grass (Ruppia maritima), filled most of the ecological niche, but it had large swings between years when the population crashed and years with recoveries. Without more stable Eelgrass coverage, the frequent bust years for Widgeon Grass left a hole at the base of estuary ecology. HOW DID IT HAPPEN? Seagrass had been struggling for some time with the effects of nonpoint source pollution, sea level rise and boating, and had seen wide losses compared to historical coverage. Rising water temperature was one more stress on Eelgrass whose optimum temperature is between 60 and 70°F. Widgeon Grass preferred warmer temperatures, with optimal growth occurring between 65 and 85°F, Thus, Widgeon Grass was able to move into the areas where Eelgrass struggled. Managers welcomed Widgeon Grass when Eelgrass could no longer thrive. Yet Widgeon Grass required more light, which made it much more vulnerable to turbidity. Widgeon Grass abundance fluctuated from low levels in wet years to high levels in dry years. HOW LIKELY IS IT? Eelgrass death and subsequent Widgeon Grass colonization have already been observed on the East Coast, and Eelgrass death has been observed on the West Coast. Summer temperatures on both the East and West U.S. coasts are already exceeding Eelgrass's optimum temperature range, and it is very likely that the area of warming will increase. While nutrient load reductions from polluted runoff may be a solution to the Widgeon Grass population crashes, it is unlikely that this will be achieved at large scales in the near term due to the diffuse nature of nonpoint source pollution. It is likely that where Eelgrass is the primary seagrass species, if it is lost and replaced, estuary ecology will suffer when Widgeon Grass crashes. OPPORTUNITIES AND CHALLENGES Facilitating the conditions for a successful transition from declining Eelgrass to healthy Widgeon Grass could serve as a model for managing other ecosystems facing changing environmental conditions. Some areas that supported Eelgrass may be environmentally unsuitable for Widgeon Grass. Southern varieties of Eelgrass that have more heat tolerance may be useful for seagrass restoration farther north. Eelgrass declines may present opportunities to educate the public on the ecosystem services that seagrass provides and their dependence on good water quality. Assessment 03-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- POLICY CONTEXT AND QUESTIONS Often restoration is the first step taken to address Eelgrass loss. However, recognizing its population declines as an effect of a zonal shift may turn policymakers toward management options to promote more heat-tolerant species. Focusing on Widgeon Grass resilience may also involve state or local regulations to reduce pollution. Controlling land-based sources and investing in stormwater management would likely decrease eutrophication-caused turbidity and help to stabilize Widgeon Grass populations. This scenario connects to sustainability goals for: clean water and sanitation sustainable cities and communities life below water. SELECTED REFERENCES Plaisted, H. K., Shields, E. C., Novak, A. B., Peck, C. P., Schenck, F., Carr, J., Duffy, P. A., Evans, N. T., Fox, S. E Heck, S. M Hudson, R., Mattera, T., Moore, K. A., Neikirk, B., Parrish, D. B., Peterson, B. J., Short, F. L, & Tinoco, A. I. (2022). Influence of Rising Wafer Temperafure on fhe Temperate Seagrass Species Eelgrass (Zostera marina L.) in the Northeast USA. Frontiers in Marine Science, 9. https://doi.ora/10.3389/fmars.2022.920699 Plummer, M,L, Harvey, C.J., Anderson, I.E. et al. The Role of Eelgrass in Marine Community Interactions and Ecosystem Services: Results from Ecosystem-Scale Food Web Models. Ecosystems 16, 237-251 (20131. https://doi.ora/10.1007/sl0021 - 012-9609-0 Waycott, M., Duarte, C. M., Carruthers, T. J., Orth, R. J., Dennison, W. C., Olyarnik, S., Calladine, A., Fourqurean, J. W., Heck, K. I., Jr, Hughes, A. R., Kendrick, G. A., Kenworthy, W. J., Short, F. T., & Williams, S. L. (2009). Accelerating loss of seagrasses across the globe threatens coastal ecosystems. Proceedings of the National Academy of Sciences of the United States of America, 106(30), 12377-12381. https://doi.ora/l0.1073/pnas.0905620106. Eelgrass bed (Zostera marina). , J.n'JPH, \M ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS The rate of sea level rise is destroying marshes. By establishing migration corridors, these coastal ecosystems can move upward and inland. As the tides extend into available adjacent sites and create new wetland conditions, salt marshes can form there while their seaward edge is drowning. ESTABLISHING MARSH MIGRATION CORRIDORS COASTAL FUTURE HOW DOES IT LOOK? As the rate of sea level rise exceeded the ability of marshes to accrete sediment, marshes were drowned and lost. Managers searched for low lying shoreline land that would be suitable for new marsh habitat. In most areas, the pace of marsh migration into available open space was slower than the rate of salt marsh loss due to sea level rise. HOW DID IT HAPPEN? In the developed areas of the country, land that was suitable for wetlands migration was scarce, acquisition often involved expensive purchases. Further, erosion control structures and impervious surfaces hindered salt marsh migration. A great deal of site preparation would be required before a site was fit for wetlands. It was very difficult to assemble large tracts with suitable land cover, topography and hydrology. In rural areas the best opportunities to establish salt marshes were flat, shoreline sites that had been in agricultural use. Although assembling large tracts was still difficult, there were successes acquiring farmland that was already having trouble with coastal flooding and salinization. Some farmers were interested in compensable conservation opportunities. States promoted and expanded tax credits for conservation easements. Local conservation trusts formed to assist landowners with the process of protecting their land under the easements. In other cases, programs for buyouts were expanded, and targeted land purchases were made to ensure corridor connectivity. Another tool, rolling easements, also became attractive as it became more widely known. These easements were triggered by a preset amount of sea level rise, but allowed continued occupation and use until that time. This put money in farmers' pockets right away, allowed for continued agriculture where it was viable, while securing future corridors for marsh migration. HOW LIKELY IS IT? Sea level rise is already causing marsh loss. State governments, nonprofit organizations and academic groups collaborate in many regions to model and identify land that is topographically and ecologically suitable for marsh migration. Land trusts and other nonprofits in some coastal states along the Atlantic and Gulf are aiding with conservation easements. Low-lying coastal cropland is widely considered an ideal setting for marsh migration, especially compared to heavily developed urban and residential areas or coastal forests. Some coastal farming communities are already experiencing salinization of cropland. It is very likely that shoreline farmland will become progressively more inarable in the Atlantic and Gulf regions due to the combined effects of sea level rise, drought, and subsidence. It is likely that as tides encroach, some rural shoreline lands will be acquired for wetlands, while it is unlikely that large corridors can be routinely assembled. Assessment 04-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- In contrast it is unlikely that many marsh migration corridors will be established where development already exists, and large corridors would be very unlikely. Buyout programs in residential settings are generally reactive and are most often used after major disasters or for repetitive flood loss properties. OPPORTUNITIES AND CHALLENGES The practice of mitigation banking already considers future site conditions, including whether a site provides an opportunity for salt marsh migration. Salt marsh habitat is a direct contributor to the health of fisheries and successful marsh migration programs could have benefits for fish. Horizontal marsh migration is represented in several modeling programs, but the real-life process of salt marsh migration is more complex than modeling is able to capture. Coastal storms vary widely in strength and number from year to year and property owner interest in buyouts is likely to increase following strong storms and fade as time goes by. Remediation may be needed for land that has historically been treated with fertilizer and pesticides. POLICY CONTEXT AND QUESTIONS Success or failure in establishing marsh migration corridors will hinge on how significant economic incentives for easements or land buyouts are and how well they will be advertised to landowners. Resistance to buyouts can be expected. Private entities could be encouraged to donate or designate land for marsh migration through the creation of pollution credit or tax credit programs, or through creative market structures that recognize the value of ecosystem services. This scenario connects to sustainability goals for: zero hunger clean water and sanitation life below water life on land. SELECTED REFERENCES Environmental Law Institute. (2024). Compensatory Mitigation: Improving Success Under Changing Circumstances. https://www.eli.ora/research-report/compensatory-mitiaation-improvina-success-under-chanaina-conditions Gibson, N., McNulty, S., Miller, C Gavazzi, M Worley, E., Keesee, D., & Hollinger, D. (2021). Identification, mitigation, and adaptation to salinization on working lands in the U.S. Southeast. Forest Service, U.S. Department of Agriculture, Southern Research Station, https://wvvw.climatehubs.usda.aov/content/identification-mitiaation-and-adaptation-salinization- workina-lands-us-southeast Fant, C., Gentile, L. E Herold, N., Kunkle, H., Kerrick, Z., Neumann, J., & Martinich, J. (2022). Valuation of long-term coastal wetland changes in the U.S. Ocean & coastal management, 226, 1-11. https://doi.ora/l 0.1016/i.ocecoaman.2022.106248 Stevens RA, Shull S, Carter J, Bishop E, Herold N, Riley CA, et al. (2023) Marsh migration and beyond: A scalable framework to assess tidal wetland resilience and support strategic management. PLoS ONE 18(11): e0293177. https://doi.ora/l 0.1371 /iournal.pone.0293177 A NRCS team surveys farmland in eastern North Carolina that is suspected to have lost productivity due to saltwater intrusion. Photo by Michael Gavazzi/USDA. Titus, J. (2011). Roiling Easements. U.S. Environmental Protection Agency: Climate Ready Estuaries Program. 179 pp. https://www.epa.aov/sites/default/files/documents/rollinaeasementsprimer.pdf ------- CLIMATE READY S T U A R I E S xvEPA FARMING BLUE CARBON COASTAL FUTURE HOW DOES IT LOOK? Natural Spartina marshes did not capture enough annua! carbon to become economically justifiable carbon market projects. Entrepreneurs with a single focus on capture and sequestration began blue carbon farming projects that could accumulate carbon more efficiently than Spartina wetlands. These designed systems did capture more carbon, but did not provide the same habitat complexity and value as the native Spartina marshes. HOW DID IT HAPPEN? Purposeful carbon farming could not happen without the promise of an economic return. Profits would only materialize by capturing enough carbon that could be verified. Efforts to maximize carbon took two paths. Plants that could capture more carbon than Spartina, such as Phragmites and mangroves were introduced. Landscape modification to improve drainage and prevent prolonged flooding was also instituted to discourage methane production. Phragmites captured more carbon but had different hydrology and nutrient cycling, and supported different wildlife than native Spartina. In salt marshes that were already infested with invasive Phragmites, landowners who were after carbon simply encouraged the Phragmites instead of working as before to restore the natural Spartina system. Phragmites was well-adapted to higher carbon dioxide, thus it grew more productively and sequestered more as levels increased. Phragmites was also well-adapted to the high levels of nitrogen pollution in estuary waters. This made Phragmites a low maintenance blue carbon "cash crop." In warmer southern regions, progressively milder winters extended the geographic range for mangroves. Entrepreneurs speculated that assisting the northward migration of carbon-dense mangroves would pay off if the trees survived the winters. Landowners altered the hydrology at their carbon farms to minimize methane production. They also blocked the natural migration of less carbon efficient Spartina into their plots. WHY THIS MATTERS Using plants to collect carbon and sequester it in coastal environments is a "blue carbon" contribution to raising resilience and resisting change. Despite ecological impacts from losing native salt marshes, a variety of plant species could sequester carbon on shoreline lands. Phragmites Assessment 05-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- HOW LIKELY IS IT? Where Spartina is viable, turning to Phragmites would very likely face opposition to its intentional use for carbon sequestration. Many local and state regulations bar planting invasive species such as Phragmites, and it is counterintuitive to many conservationists to protect it. Further, some studies indicate that Phragmites releases more methane than Spartina, offsetting some of the carbon benefits. Whereas translocating mangroves would replace ecologically appropriate native wetland species, this has a better chance to be accepted by conservationists, since mangroves are native to southern U.S. coastlines. Acceptance of assisted migration may still be unlikely because of wariness or resistance to the concept. Yet where mangroves can survive, warmer winters are probably bringing mangroves anyway. Markets already exist, and it is very likely that the mechanisms for accrediting blue carbon ecosystems will continue to advance. While growing Phragmites seems like a zero-effort proposition, the costs of monitoring and accounting that are required to participate in the marketplace are likely to outpace the revenue from credits in a modest farming operation. Similarly, the cost of establishing a new, viable Spartina marsh would be very high compared to what it can sequester. Unless the value of carbon becomes many fold its current price it is very unlikely that shoreline carbon farming will be a primary activity. There is a possibility that a co-op or sponsor could relieve participating landowners of some overhead expenses, although this too would depend on the amounts that could be credited and its price. OPPORTUNITIES AND CHALLENGES The relative ability of Spartina and Phragmites to sequester carbon still requires research, and markets need to account for externalities such as methane. Phragmites produce biomass at a faster rate than Spartina and could generate co-benefits of increased vertical accretion and wetlands resilience to sea level rise. Mangroves are moving northward, regardless of whether their migration will be assisted. POLICY CONTEXT AND QUESTIONS Perhaps the biggest hurdle in conserving and restoring ecosystems through market mechanisms is actually the creation of a robust, accessible, blue carbon market. National accounts as well as blue carbon credits may need to adjust when wetland vegetation changes (e.g., from Spartina to Phragmites or from Spartina to mangroves). The question of regulation for intertidal "agriculture" and uncertainty about ownership of intertidal lands remain to be resolved. The importance of carbon capture vs. the importance of high value native habitat could also confront policy makers who would want both. This scenario connects to sustainability goals for: zero hunger clean water and sanitation decent work and economic growth responsible consumption and production life below water life on land. SELECTED REFERENCES Emmer, I., Needelman, B., Emmett-Mattox, S., Crooks, S., Beers, L, Megonigal, P., Myers, D., Oreska, M., McGlathery, K., Shoch, D., (2023). Methodology for tidal wetland and seagrass restoration. Verified Carbon Standard. https://verra.ora/methodoloaies/vm0033-methodoloav-for-tidal-wetland-and-seaarass-restoration-v2-l / Macreadie, P.I, Costa, M.D.P., Atwood, T.B. et al. Blue carbon as a natural climate solution. Nat Rev Earth Environ 2, 826-839 (2021). https://doi.ora/10.1038/s43017-021-00224-l ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Sea level rise increases the extent and frequency of tidal flooding, challenging shoreline municipalities that have combined stormwater and sanitary sewer systems. Reengineering these systems to keep tidal floodwater out of the combined piping enables communities to avoid harmful sewage outflows. REENGINEERING COMBINED SEWER SYSTEMS COASTAL FUTURE HOW DOES IT LOOK? Sea level rise led to higher tides moving inland. In low-lying areas of coastal communities with combined sewers, tidal flooding eventually began finding its way to street catch basins and flowed down into the pipes. Backflow preventers kept the tide from entering the sewer system directly through outfalls. In contrast surface tidal flooding entered the sewers through catch basins that were designed to collect runoff. Tidal flooding overwhelmed the pipes and produced sewage outflows just as high rainfall did. To stop these sewage outflows and their ensuing problems, communities on tidal shorelines began reengineering their combined sewer systems. HOW DiD IT HAPPEN? As tidal flooding became more frequent, strategies that worked to prevent rainfall-driven overflows, such as green stormwater infrastructure or underground storage proved ineffective. Combined sewer systems became overwhelmed by frequent high tide flooding events. Other available strategies included dikes or floodwalls to protect vulnerable low-lying catch basins. In some cases, stormwater runoff became trapped behind these walls, inadvertently leading to other drainage issues. Though expensive, some communities reconstructed their combined, single pipe systems as separate sanitary and storm sewers to avoid having tidal inflow in their sanitary sewer systems. Those communities eliminated the occurrence of all combined sewer overflow events because rainfall no longer entered sanitary sewers through stormwater catch basins. HOW LIKELY IS IT? Combined sewer outflows cause severe negative impacts to public health, public safety, water quality, and public finances. Because of accelerating sea level rise, coastal flooding is becoming more frequent and flooding incidents will increase. It is very likely that coastal communities with tidal flooding problems will be forced to address their combined systems. Communities are likely to want to use strategies that were designed to address rainfall-driven overflows because of their familiarity; however, as time goes by the scale and frequency of tidal flooding poses challenges that these strategies cannot address. Communities may be drawn to the additional protection from dikes or floodwalls, but the inability of stormwater runoff to drain to open water will raise concerns. Recognizing the limitations of these alternatives, it is very likely that exposed shoreline communities will elect to separate the vulnerable sections of their combined systems into separate sanitary and stormwater pipes. The timing will be influenced by the onset and scale of the problem, funding, and the availability of technical assistance. - Assessment 06-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES Separating systems to avoid tidal inflow will stop combined sewer overflows, improve aquatic habitat, enhance water quality, decrease public exposure to pathogens, and improve recreation opportunities. Dikes and floodwalls will need to be reinforced intermittently to increase their stability and resistance against breaching events as continuing sea level rise poses new flooding challenges. POLICY CONTEXT AND QUESTIONS Recent assessments of combined sewer system locations indicate that overflows can disproportionately affect low-income communities and communities of color in urban areas. Policymakers will need to consider how to analyze risks, distribute the cost burden of separating sewer systems, pay for improvements, and protect communities. As the area subject to tidal flooding expands, more coastal communities will be challenged to meet their short-term and long-term plans for combined sewer overflow abatement. States may struggle to meet water quality standards If outflows increase. Policymakers may be forced to revisit compliance schedules and regulations to determine whether adjustments are needed to address new threats. This scenario connects to sustainability goals for: good health and well-being clean water and sanitation industry, innovation and infrastructure reduced inequalities sustainable cities and communities life below water peace, justice and strong institutions. In places with combined sewer systems, if high tide floods into the community, then water can still be draining into catch basins after the tide level drops. This can surcharge the pipes and trigger a sewage outflow (Climate Ready Estuaries/Horsley Witten Group). SELECTED REFERENCES Government Accountability Office. Clean Wafer Act: EPA Should Track Control of Combined Sewer Overflows and Wafer Quality Improvements. GAO-23-105285, 2023. Hummel, Michelle A., Berry, Matthew S., and Stacey, Mark T. Sea level rise impacts on wastewater treatment systems along the U.S. coast.';. Earth's Future, 6 (2018): 622-633. Sweet, William V. et al. Global and Regional Sea Level Rise Scenarios for the United States: Updated Mean Projections and Extreme Water Level Probabilities Along U.S. Coastlines. NOAA Technical Report NOS 01. National Oceanic and Atmospheric Administration, National Ocean Service, (Silver Spring, MD: 2022). U.S. Environmental Protection Agency. Report to Congress: Impacts and Control of CSOs and SSOs. EPA 833-R-04-001, 2004. ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Sea level rise and storms impair and damage water infrastructure, necessitating reinvestment and greater maintenance. Frequently repairing and rebuilding these systems will increase utility costs, and long time residents may be forced out by escalating bills or taxes. PAYING FOR NEW WATER INFRASTRUCTURE COASTAL FUTURE HOW DOES IT LOOK? The effects of sea level rise and more intense and frequent storms began to have increased fiscal impacts on coastal communities. Infrastructure challenges came from saltwater intrusion in drinking water sources, higher groundwater tables, floods, and storms. There were ever rising costs for system maintenance, repair, and replacement. The escalating expense of upgrading and operating stormwater, wastewater, and drinking water utilities was being passed to taxpayers and ratepayers. Some homeowners incurred personal expenses for their private wells or wastewater systems. Eventually the cost burdens began pushing long- time residents to move away. HOW DID IT HAPPEN? Coastal communities faced numerous hazards and accelerating sea level rise increased their risk. Greater infrastructure expenses were inevitable. While some needs were addressed through routine upkeep, many communities faced costly options of elevating, hardening, and relocating facilities (many of which by function and design were located in low-lying areas). Assets such as new drinking water sources or desalination capacity were needed to address saltwater intrusion into aquifers and increased salinity in coastal rivers. Residents were also affected by special assessments or special service districts, which impose levies for capital improvements. The bond market reacted to new risks by seeking higher interest, whether the risks came from exposure to a changing environment or from borrower capacity. As costs were passed along, some residents found the burden too high and were forced to move. For smaller water utilities, with smaller ratepayer pools and limited capacity to access alternative funding, the dwindling number of residents and revenue only exacerbated the situation and raised compliance challenges. Unless rate increases were paired with low-income assistance, households faced the threat of utility shut offs. Unless new residents replaced those who moved away, those who remained faced even higher cost burdens. HOW LIKELY IS IT? Coastal areas face numerous hazards and accelerating sea level rise will continue to increase the risk from floods and storms. Vulnerable coastal communities must either adapt or be harmed by impacts, thus higher infrastructure expenses are inevitable. Utilities that use scenarios of future conditions to inform their capital investments can raise their system resilience. Although there are federal grant and loan programs, local governments and utilities are very likely to continue spending their own resources on water infrastructure. Residents will shoulder many of these costs through local taxes and fees. The availability of income-based assistance programs to buffer these impacts will very likely have geographic variability as seen with most state and local programs. As environmental stress accumulates in coastal communities, it is very likely that residents with limited financial means will factor all of their household expenses, including utilities, into their decisions to remain or move away. Assessment 07-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES Coastal infrastructure resilience can be increased through risk assessments and adaptation planning. When feasible, utility resilience could also be incorporated into other necessary work such as highway maintenance or shore protection projects. People who have trouble affording rising utility bills would also have trouble paying to repair their own storm damage. Underrepresentation of marginalized groups within policymaking spaces may be reinforced by out-migration, leading to coastal communities constituted predominantly by those who can afford the rising costs of adaptation. Construction may become a more frequent occurrence in coastal communities as utilities increasingly need upgrades and repairs. POLICY CONTEXT AND QUESTIONS A focus on efficiency, water conservation and treatment could reduce the need for some capital investments. Technical assistance could raise the capacity of small systems to manage loans and grants and to submit competitive proposals. Restructuring or regionalizing utilities, while not necessarily a federal goal, has been used to manage affordability. Federal programs are not generally designed to assist individuals who want to relocate because they face rising household expenses. While managed retreatthe purposeful coordinated movement of people away from risksis intended to retain social and community ties, relocating due to unaffordability could be considered as one-by-one unmanaged retreat. The EPA's Financial Capability Assessment Guidance (FCA Guidance) is used by municipalities when devising plans to come into compliance with the Clean Water Act. Similarly, State Revolving Fund programs have affordability criteria based on financial capacity and can provide very low interest rates or loan principal forgiveness. FCA and SRF examples, along with practices of other federal programs that help with energy costs, may have wider applicability. This scenario connects to sustainability goals for: no poverty clean water and sanitation industry, innovation and infrastructure reduced inequalities peace, justice and strong institutions. SELECTED REFERENCES U.S. Environmental Protection Agency. Clean Wafer Act Financial Capability Assessment Guidance. 800b21001, 2023. U.S. Environmental Protection Agency. Financing Decentralized Wastewater Treatment: Systems Pathways to Success with the Clean Water State Revolving Fund Program. 832-R-22-001, 2022. U.S. Environmental Protection Agency. Assistance That Saves: How WaterSense Partners Incorporate Water Efficiency Into Affordability Programs. 832-F-21 -016, 2021. Association of State Drinking Water Administrators. State Drinking Water Program Challenges and Best Practices: Small and Disadvantaged Wgfer System Funding and Assisfgnce. 2022. EPA's Creating Resilient Water Utilities initiative ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS As the U.S. seeks to develop new energy capabilities, the open water of coastal bays will be an enticing place to generate electricity using wind, solar, wave or tidal systems. Yet realizing this industrial potential will be challenged by operational constraints, environmental questions, and looming siting conflicts. GENERATING ELECTRICITY WITHIN ESTUARIES COASTAL FUTURE HOW DOES IT LOOK? The push to generate electricity for a growing population and economy led the energy industry to the wide-open spaces of the country's estuaries. Environmental conditions such as unblocked sunlight, constant winds, and perpetually ebbing or flooding tides were recognized as conducive for local energy production to supply the coastal towns and cities. Wind turbines, solar arrays, wave harnessing devices and tidal power systems are now located on the shorelines and throughout the open water too. HOW DiD IT HAPPEN? As energy development expanded, coastal states developed incentives as well as permitting and siting protocols to weigh competing uses in estuaries. Although they had less wind potential and less space than marine sites, building estuarine facilities sidestepped some of the significant access, distance, and environmental challenges associated with working offshore. Unshaded sunlit bays with practically 360° views to the horizon also became home for solar electricity generation. It was inexpensive to load barges with solar panels and array and moor them in place. In contrast, while the tides were always flooding and ebbing, tidal electricity was geographically constrained: a suitable height range or adequate current velocity was required for economical power generation. Tidal power was practical in a few areas, but it was not a new idea and it had already been adopted in most places where it made sense. Wave energy in estuaries also had geographical constraints, and viability was limited to the largest most open bays. Over time technology and battery capability advanced, such that off-the-shelf wave systems and small tidal turbines were meeting modest needs, similar to how solar power was used for small closed systems that do not connect to the grid. HOW LIKELY IS IT? New energy technologies are increasingly coming online. Estuaries are attractive locations that sidestep issues of limited space and next-door neighbors that hinder on-land energy development. Yet stakeholder conflicts have been seen with inshore aquaculture and offshore turbines which suggest hurdles that loom for significant energy infrastructure in estuaries. Additionally, the wind and wave potential of estuaries is small compared to marine locations. Wind turbines are used in estuaries, often to provide power to specific facilities such as wastewater treatment plants. They are very likely to see increased use, especially at single facilities, although the extent to which bays will be filled to operational capacity will largely depend on area use conflicts, microeconomics, and local wind power potential. It is likely that small self-contained wind turbines, such as those found on cruising sailboats will find greater use, especially if utility costs rise. In contrast to wind power's reduced potential compared to adjacent marine settings, the solar energy potential of open estuaries is probably greater than nearby terrestrial sites. The sky exposure is very high for floating arrays, and they Assessment 08-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- don't need to take up usable space on land. Floating solar arrays have been installed in reservoirs, but their use in coastal waters is more problematic due to salt and salt spray, as well as tidal currents and height changes. Further, waves and storm surge introduce maintenance challenges. Smaller floating arrays, perhaps moored at piers, are likely, as they are more practical for more locations and applications. Large area installations may face use conflicts with fishing, recreation, and navigation. Additionally, systems may also need to be offline or protectively removed for a window of time before and after severe weather. Floating solar power systems that take up a significant portion of a bay are unlikely. Tidal power from impoundments or tidal currents is not new and has largely been evaluated. Much of the country's estuaries are microtidal and probably unsuitable. Tidal power is very unlikely to become an important source of electricity in new places. If the equipment cost is comparable to solar, then small scale, single user, shoreline wave systems could be used near the water, in special cases such as to power equipment or lights. OPPORTUNITIES AND CHALLENGES The need for a skilled workforce to build and maintain open-water energy technologies and to develop supporting infrastructure and supply chains could support job development in coastal communities where construction and maintenance activities would be based. The addition of commercial-scale projects could improve the reliability and resilience of the local grid system. The environmental impacts of large installations in bays, including shaded bottoms or effects on fish, marine mammals and birds will need assessment. Long-term coastal evolution from sea level rise, coastal storms, or population movement can change the operational considerations for power generation. POLICY CONTEXT AND QUESTIONS As seen with all energy sources, favorable government incentives influence industry investments. Increasing pressure to satisfy public demand may produce proposals for siting in the open space of coastal bays. Most of those spaces are publicly owned. Concerns with estuary energy generation include impacts to water quality, ecological impacts, rights to submerged lands, and competing uses such as fishing and boating. Environmental impacts could be large and increase as installations get bigger or more prominent. As with any energy project, there are complex siting and permitting challenges, and a multifaceted system of federal, state, and local rules and regulations. This scenario connects to sustainability goals for: affordable and clean energy decent work and economic growth industry, innova tion and infrastructure sustainable cities and communities life below water. SELECTED REFERENCES DOE. (2019). Powering the Blue Economy: Exploring Opportunities for Marine Renewable Energy in Maritime Markets. Office of Energy Efficiency gnd Renewgble Energy. Kircher, L., Fogorty, M., gnd Lgwson, M. (2021). Morine Energy in the United Stgtes: An Overview of Opportunities. Notionol Renewgble Energy Lgborotory. NREL/TP-5700-78773. Johnson Controls and GRID work with volunteers assembling and installing a floating PV array on a Walden water retention pond at the City's water facility in Walden, CO (U.S. Department of Energy). Pologye, B., Vgn Cleve, B., Copping, A., grid Kirkendgll, K. (2011). Environmentol effects of tidol energy development. U.S. Depgrtment of Commerce, NOAA Technicol Memo. F/SPO-116. ------- CLIMATE READY ESTUARIES vvEPA WHY THIS MATTERS Sea level rise and storms are leading communities to gates that close off an estuary from the sea to reduce their risks from flooding. Barriers must close in advance of floods and those levels are reached more often due to sea level rise. By truncating the tidal cycle, gate closures change hydrology and ecological systems TRUNCATING THE TIDE COASTAL FUTURE HOW DOES IT LOOK? When cities turned to surge barriers as their preferred way of protecting against coastal storms and sea level rise, they saw no further need for duplicative on-land hazard mitigation measures. Consequently, as sea level rise progressed, the gates were closed more and more frequently to prevent flooding. This operating procedure produced a truncated tidal cycle in estuaries, with reduced tidal range, and produced long periods of still water when the gates were shut. HOW DID IT HAPPEN? Surge barriers were constructed across inlets and river mouths. While barrier design varied by location, all incorporated movable gates that closed to protect areas behind the barrier from storm surge and tidal flooding. Most barrier designs included closed spans that reduced the distance across the estuary mouth and constricted tidal flow to narrower openings. Gates did not close quickly; thus closures needed to begin long before high tide. Gates remained closed until water levels equalized on both sides of the barrier, a process that sometimes spanned a few days for strong storms. As sea level rise progressed, surge barriers closed more frequently in response to routine tides that began to cause flooding at levels that used to only be seen during storms. When open, locally increased tidal velocities were seen at the barrier gateswhich posed challenges to navigation. Closing the gates reduced tidal amplitude, altered tidal mixing and salinity, introduced stratification, and affected sediment transport within the estuary. In some instances, while surge barriers successfully protected development from ocean storm surge, concurrent rain and high river levels led to flooding behind the closed gates. HOW LIKELY IS IT? It is very likely that coastal hazard risk and severity will increase in response to sea level rise and changes in extreme weather patterns, necessitating mitigation strategies. Already, some existing surge barriers are being closed more frequently rather than just for the extreme storms they were originally designed to protect against. Several U.S. coastal regions are considering surge barriers as an integral element of resilience and adaptation planning. Surge barriers are included in the tentatively selected plans in recent coastal risk management studies, including for the New Jersey Back Bays, New York- New Jersey Harbor and Tributaries, and coastal Texas regions, though they are paired with other coastal hard infrastructure and nature-based solutions. It is very likely that surge barriers will lead to both acute and chronic impacts to estuaries, though the exact nature of impacts is influenced by surge barrier design (e.g., barrier and gated opening lengths), estuary characteristics (e.g., stratification type, sedimentary transport, hydrodynamics), frequency and duration of gate closures, and climatic conditions (e.g., drought). Scientific research and modeling on a limited selection of extant and proposed barriers demonstrate impacts to tidal flow, exchange, mixing, and velocities, with cascading effects to other estuary conditions such as tidal amplitude. Assessment 09-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES There is a continued need for research on the chemical, physical and biological effects of surge barriers and their operationfor the decades (and centuries) that they will be in place, While existing barriers may serve as case studies, few of these barriers are of the scale being considered for implementation in U.S. coastal cities. Frequent openings and closures may reduce the operational lifespans of these structures. On-land flood mitigation may still be needed for protection against smaller flood events or induced flooding. As surge barriers close more frequently, and possibly for longer durations, coastal cities may find that interrupted tidal processes and trapped pollutants behind the barrier contribute to water quality impairments and habitat degradation. POLICY CONTEXT AND QUESTIONS Sea level rise and changes in extreme weather patterns will continue to force U.S. coastal cities to confront how much flooding is acceptable. Over time, barrier managers will need to consider adjustments to the water level closure criteria to limit increasingly frequent and long closures: cities will need a greater tolerance for flooding or must adopt other mitigation measures. For some communities, surge barrier proposals can raise questions about which populations, infrastructure, and neighborhoods are protected and which ones are not protected (or even which will face increased potential for harm via induced flooding). Cities may also see increased development behind surge barriers in locations that some will believe are safe from coastal storms and flooding. This scenario connects to sustainability goals for: sustainable cities and communities life below water. SELECTED REFERENCES Chen, Z., & Orton, P. M. (2023). Effects of storm surge barrier closures on estuary saltwater intrusion and stratification. Water Resources Research, 59, e2022WR032317. https://doi.ora/10. l029/2022WR032317 Orton, P., Ralston, D., van Prooijen, B., Secor, D., Ganju, N., Chen, I., et al. (2023). Increased utilization of storm surge barriers: A research agenda on estuary impacts. Earth's Future, 11, e2022EF002991. https://doi.ora/l 0.1029/2022EF002991 Ralston, D. K. (2022). Impacts of storm surge barriers on drag, mixing, and exchange flow in a partially mixed estuary. Journal of Geophysical Research: Oceans, 127, e2021 JC018246. https://doi.ora/l 0.1029/2021JC018246 MULTIPLE LINES OF DEFENSE ON THE TEXAS COAST Galveston Seawall Improvements Illustration is representational and not to scale Bolivar and West Galveston Beach and Dune System Bolivar Roads Gate System Concept for gates and other coastal storm risk management measures at Galveston Bay. Image from the Coastal Texas Study, Story Map Homepage fhttps://coastal-texas-hub-usace-swa.hub.arcais.com/ downloaded Oct. 24, 2024). ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Ocean and coastal acidification can harm marine life: especially calcifying species like shellfish. Managing refuge areas in estuarine waters could allow for some aquatic habitats and populations to persist. PROVIDING REFUGE FROM ACIDIFICATION COASTAL FUTURE HOW DOES IT LOOK? Ocean acidification, which was exacerbated by additional natural and anthropogenic factors (e.g., storm and seasonal upwelling, freshwater mixing, nutrient runoff, phytoplankton and algal blooms), turned once rich estuarine habitats into stressful places for aquatic life. Calcifying organisms were particularly affected as waters became more acidic and carbonate ion concentrations decreased. In an effort to preserve foundational species such as clams and oysters, water chemistry was managed in small parts of estuaries to create acidification refuges. HOW DID IT HAPPEN? Attempts to directly manipulate acidification in estuaries took two forms. In the first, macroalgae and seagrasses were deployed to augment local photosynthesis and thereby alter the immediately surrounding water chemistry. In the second, calcium carbonate such as from recycled clam and oyster shells was added to bay sediments. Other management measures addressed nonpoint source nutrient pollution that exacerbated acidification. This had a further benefit of improving conditions for submerged aquatic vegetation. The aquaculture industry also actively managed oysters through sensitive life cycle stages. Water chemistry monitoring allowed the industry to handle pH and chemical variability caused by natural upwelling and other factors. Other industry strategies included selective breeding for acidification-resistant broodstock and increasing production levels to account for mortality. HOW LIKELY IS IT? It will not be possible for local management of estuaries to reverse marine trends. Yet estuary management can have some impact on local water chemistry. Because coastal and estuarine waters are particularly susceptible, and threats to some aquatic species have significant economic implications, state and federal agencies have developed research priorities and management strategies for ocean and coastal acidification and it is very likely that this will continue. Directly introducing carbonate with recycled oyster shells has been tested in experimental plots. This has some potential to change sediment carbonate levels where they are placed, although effects diminish over time. It is about an even chance that with active and ongoing replenishment, sedimentary carbonate could be boosted with shell hash. The effectiveness of submerged aquatic vegetation in controlling pi I is highly variable and transient. While otherwise SAV has an important ecological role, it is unlikely to be an effective management strategy for the problem of acidification. The effects of nonpoint sources of pollution become even more problematic as water temperatures increase, and their further interactions with ocean acidification will become apparent. Increased control of nonpoint source pollution will be necessary to reduce its contribution to acidification. Nutrient management with seaweed is an emerging area of interest that is likely to be pursued for that reason, and this will have some co-benefits for addressing coastal acidification. Assessment 1 0-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- The oyster aquaculture industry is already actively managing operations to reduce the effects of acidification. Water intake monitoring, pl-l management, and bioengineeririg were seen in the 2010s and are very likely to continue and be more widely adopted. Some industry relocation has occurred and is as likely as not to continue, largely dependent on the place-based effects of acidification and the ability to mitigate its impacts. OPPORTUNITIES AND CHALLENGES Previous episodes of acidification mortality in the shellfish industry have spurred the development of partnerships with industry, agencies, and academia. The stress from the increasing acidification of the ocean and the tidal mixing of seawater into estuaries will never be eliminated, and is projected to grow worse in coming decades. Within larger estuaries where water chemistry has persistent spatial variability, affected uses might be relocatable to more favorable zones if suitable sites are available. Pteropod affected by ocean acidification. Its shell ridges are dissolving, and shell fractures, weak spots, and cloudy areas are also visible (NOAA News April 30, 2014). POLICY CONTEXT AND QUESTIONS Water use conflicts are not uncommon with aquaculture operations, and expansions of macroalgae aquaculture may encounter these tensions. State and federal agencies are producing strategic research and response plans to ocean acidification that provide a blueprint for experimentation and adaptation responses. Nonpoint source pollution has been difficult to control without explicit legislative authorization, yet it is a critical element in responding to coastal acidification. The question of impairments due to acidification are expected to increasingly occur and arise in listing decisions under Clean Water Act 303(d) and TMDLs. This scenario connects to sustainability goals for: clean water and sanitation sustainable cities and communities life below water. SELECTED REFERENCES National Oceanic and Atmospheric Administration. Ocean, Coastal, and Great Lakes Acidification Research Plan: 2020- 2029, edited by Jewett, Elizabeth B., Emily B. Osborne, Krisa M. Arzayus, Keriric Osgood, Benjamin J. DeAngelo and Jennifer M. Minfz. 2020. California Ocean Science Trust. Emerging understanding of the potential role otseaarass and kelp as an ocean acidification management tool in California. Nielsen, Karina J., John J. Stachowicz, Katharyn Boyer, Matthew Bracken, Francis Chan, Francisco Chavez, Kevin Hovel, Kerry Nickolks, Jennifer Ruesink, and Joe Tyburczy. Oakland, California. 2018. Washington Marine Resources Advisory Council. 2017 Addendum to Ocean Acidification: From Knowledge to Action, Washington State's Strategic Response, edited by Enviroissues. Seattle, Washington. 2017. California Ocean Science Trust. The West Coast Ocean Acidification and Hypoxia Science Panel: Major Findings, Recommendations, and Actions, by Chan, Francis, Alexandria Boehm, Jack Barth, Elizabeth Chornesky, Andrew Dickson, Richard Feely, Burke Hales et al. Oakland, California. 2016. ------- CLIMATE READY S T U A R I E S xvEPA LOWERING STREAM TEMPERATURE COASTAL FUTURE HOW DOES IT LOOK? Streams, lakes, and estuaries got progressively hotter as time went on. A variety of cold- water fish such as salmon and trout saw their range shrink to a few refuge areas. Some went extinct as the last of their habitat became too hot. Many of these fish were iconic or culturally significant. In an attempt to save what could be saved, there was a concerted effort to control stream temperature. Any technique to lower water temperature in a pond or a first- order stream was implemented. These measures were expensive, and people debated their value and long- term effectiveness. HOW DiD IT HAPPEN? Traditional techniques for lowering water temperature were implemented first. Combinations of in-steam measures (e.g., removing obsolete dams and impoundments, creating deep pools or artificial logjams), groundwater measures (e.g., promoting stormwater infiltration, removing channelization) and land use measures (e.g., planting trees, restoring upland riparian areas) to reduce water temperatures had varying impacts. As warming continued more radical steps were tried. Reflective material was used to cover reservoirs and ponds. Some places opted for cooling towers such as those used to lower the temperature of industrial discharges. Refrigeration was pursued to preserve endangered species on the most critical stream reaches. On the hottest days some environmental managers tried to directly lower water temperature by dumping ice. HOW LIKELY IS IT? Because many of the land use and hydrological measures used to control water temperature have multiple benefits for other environmental management goals it is likely that they will be used if temperatures approach critical levels. However, some of these techniques, such as tree planting, are not quick solutions and cannot be effective on short time scales. Reflective material and blankets have been used to keep the sun off of glaciers to stop melting, and drinking water reservoirs and aqueducts have been covered with floating covers and "shade balls" to reduce evaporation or control algae. It is about an even chance that where feasible these techniques could be used to limit solar heating in aquatic habitats on the hottest days. Chilling and evaporation have been used to mitigate point sources of thermal pollution, and dumping ice might be used to lower water temperature in small impoundments or headwaters by 1 ° or 2°however for general environmental management these are speculative ideas with no known examples. Although it would only be needed to keep temperature below ecological thresholds on the hottest days, chilling would be a desperate measure and very unlikely to be widely used due to logistics, cost, uncertainty, and perception that it would be just a short-term patch. WHY THIS MATTERS The temperature in streams and waterbodies continues to warm, creating major threats to sensitive fish and aquatic life. Adopting targeted and intensive interventions could be a last effort to lower tributary temperatures and maintain critical habitat for important species. Assessment 1 1 -2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES Adopting these techniques may lead to co-benefits such as restored natural hydrology, improved water quality, and the creation of new habitat for aquatic flora and fauna. Locational decisions and best management practices may need to be updated regularly as temperatures continue to rise. Existing development may hinder the adoption of temperature reducing measures such as the removal of obsolete dams and impoundments or the removal of channelization because these strategies could impact flooding. Techniques that can lead to some water temperature reduction may fail to provide enough after further warming. Efforts to lower stream temperature may not be sufficient and durable, they may simply delay the inevitable. POLICY CONTEXT AND QUESTIONS Some measures to lower stream temperature are not quick fixes and it may be too late to use them if temperature thresholds are approaching. Advanced planning, significant engineering analysis, and time for permits and construction need to be factored in. Some of the simpler and easier concepts, such as planting trees, can take years before there is adequate shading. Higher water temperature may challenge states with water quality standards related to heat. Policymakers may be forced to revisit regulatory approaches to determine whether adjustments are needed. This scenario connects to sustainability goals for: clean water and sanitation sustainable cities and communities life below water life on land. SELECTED REFERENCES Batiuk, Rich el al. Rising Watershed and Bay Water Temperatures: Ecological Implications and Management Responses - A STAC Workshop. STAC Publication Number 23- 001. January 20, 2023. Oregon Department of Fish and Wildlife. The Oregon Conservation Strategy: Climate Change and Oregon's Estuaries. n.d. Thompson, Jonathan. Keeping it cool: unraveling the influences on stream temperature. Science Findings 73, (2005). U.S. Environmentoi Protection Agency. Actions That Could Reduce Woter Temperature, Appendix F. Being Prepared for Climate Change: A Workbook for Developing Risk-Based Adaptation Plans. EPA 842-K-14- 002, 2014. Newly-planted vegetation along the Shasta River. Monitoring of the project has shown a significant decrease in summer water temperatures. Erika Nortemann/NOAA ------- CLIMATE READY S T U A R I E S xvEPA MINDING DEOXYGENATION COASTAL FUTURE HOW DOES IT LOOK? Warmer ocean water temperature directly reduced the physical capacity of seawater to hold dissolved oxygen. Many estuarine and coastal waters already had unique hypoxia problems resulting from land-based sources of pollution and other human activity. While nutrient driven hypoxia in coastal waters continued to resist solutions, reduced oxygen capacity due to warming made estuary recovery more difficult and pushed marginal places into hypoxic states. HOW DID IT HAPPEN? The main mechanisms through which warming water temperature contributed to oxygen stress in coastal waters was by lowering the physical ability to hold dissolved oxygen and by induced stratification that isolated bottom water. Sea level rise increased estuarine salinity which also led to lower oxygen solubility. As temperatures rose, estuaries entered hypoxic states when oxygen was depleted. More waters showed signs of hypoxia and became more sensitive to the negative water quality impacts of nutrient loading. As warming continued, coastal and estuarine areas were being added instead of removed from impaired waters lists. HOW LIKELY IS ST? In marine waters, 0.5-3.3% of dissolved oxygen was lost from the upper 1000 m between 1970 and 2010. Half of this decline is attributed to solubility reduction, and the balance to stratification, circulation and other factors. The mechanisms for deoxygenation in estuaries are similar: the questions are about the likelihood and the magnitude of the impact. It is very unlikely that an estuary with good water quality will become hypoxic due solely to the lower dissolved oxygen capacity of warmer water. Marine water at 100°F can still hold 5.5 mg/l of dissolved oxygen. The main path by which warming can impact oxygen levels seems to be through stratification. Where stratification exists it is about an even chance that it will strengthen, and elsewhere Assessment 1 2-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 WHY THIS MATTERS Warmer temperature lowers the capacity of water to hold dissolved oxygen, and increases the potential for stratification which can lead to lower bottom oxygen levels. Warmer water can intensify the hypoxia already seen in so many U.S. estuaries, and can tip other places into this impaired condition. Dissolved oxygen solubility (mg/l at 760 mm Hgj Salinity 40°F 50°F 60°F 70°F 80°F 90°F 100°F 0 12.96 11.29 9.96 8.90 8.02 7.28 6.64 5 12.53 10.93 9.66 8.64 7.79 7.08 6.47 10 12.12 10.59 9.37 8.39 7.58 6.89 6.30 15 11.72 10.26 9.09 8.15 7.37 6.71 6.14 20 11.33 9.93 8.82 7.91 7.16 6.53 5.98 25 10.95 9.62 8.55 7.69 6.97 6.36 5.83 30 10.59 9.32 8.30 7.46 6.77 6.19 5.68 35 10.24 9.02 8.05 7.25 6.58 6.02 5.53 Source: Dissolved oxygen solubility tables https://water.usas.aov/water- resources/software/DOTABLES/ ------- when hydrology is conducive to stratification it can emerge. Whether new or intensified stratification will have the strength or duration to produce hypoxia depends on the unique circumstances of every place. Areas that already have low oxygen would be the most susceptible. OPPORTUNITIES AND CHALLENGES Reductions in eutrophication-induced hypoxia could outweigh any increases in hypoxia due to change in temperature. Hypoxic conditions can drive finfish to swim away from impacted areas and can have lethal effects for stationary organisms. POLICY CONTEXT AND QUESTIONS A great number of U.S. estuaries experience hypoxic conditions. Water temperature increases are an additional stressor. More estuaries that are currently marginal can be expected to start having hypoxic events. Consideration of greater controls for point and nonpoirit source pollution may be due. This scenario connects to sustainabiiity goals for: clean water and sanitation sustainable cities and communities life below water. Change in number of U.S. coastal areas experiencing hypoxia from 12 documented areas in 1960 to over 300 in 2008. Coastal Areas Experiencing Hypoxia (Committee on Environment and Natural Resources. 2010. Scientific Assessment of Hypoxia in U.S. Coastal Waters. Interagency Working Group on Harmful Algal Blooms, Hypoxia, and Human Health of the Joint Subcommittee on Ocean Science and Technology, https://cfpub.epa.aov/si/si public record report.cfm?Lab=NHEERL&dirEntrvld=213608 ) SELECTED REFERENCES K.E., Hinson, M.A.M., Freidrichs, R.G., Najjar, M.. Herrmann, 7.., Bian, G Bhatt, P., St lauienl, II., Tian, G., Shenk. (2023). Impacts and uncertainties of climate-induced changes in watershed input on estuarine hypoxia. European Geosciences Union, https://www.usas.aov/publications/impacts-and-uncertainties-climate-induced-chanaes-watershed-inputs- estuarine-hvpoxia Changing Ocean, Marine Ecosystems, and Dependent Communities. Special Report on the Ocean and Cryosphere in a Changing Climate, https://doi.ora/10.1017/9781009157964.007. Sixth Assessment Report, Working Group 1: The Physical Science Basis. Chapter 5: Global Carbon and other Biogeochemical Cycles and Feedbacks. 5.3.3.2 Ocean Deoxygenation and its Implications for Greenhouse Gases https://www.ipcc.ch/report/ar6/wa1 /chapfer/chapter-5/#5.3%20%205.3.3.2 ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Marine areas have become prone to heatwaves of several days when water temperature is very high. As unusually warm seawater flows into estuaries their temperature rises too. These events have had notable social, economic and environmental impacts that offer a glimpse of the future and the need for adaptation. ENDURING MARINE HEATWAVES T" , MfcO-"-15,. , iBP^P liLH M ...iMAIto to <5=3 J J hh a, A MlJ COASTAL FUTURE HOW DOES IT LOOK? Warming ocean temperatures and marine heatwaves (periods of persistent anomalously warm ocean temperatures) diffused into estuaries with notable effects. Heatwaves became increasingly frequent and were an obstacle to clean water management goals. While managers could do little to influence coastal water temperature, heatwaves provided previews of effects to come when warmer water would be the norm. HOW DID IT HAPPEN? Ocean temperatures were naturally variable in response to regional-scale heat transfer, warming processes and the influence of broader climate modes. However, oceans did continue to generally accumulate heat and marine heatwaves occurred more frequently. U.S. coasts experienced heatwaves of varying intensity and duration and the warm ocean water was brought into estuaries by tides. In estuaries heat was associated with algae blooms, bacteria, stress on immobile organisms including submerged aquatic vegetation, exacerbation of low oxygen states, and temporary biological shiftsboth in and out. While of limited duration, heatwaves were harbingers of future conditions. Temperature-sensitive and immobile marine organisms, as well as those at the warm (usually southern) edge of their distribution range, were the most vulnerable to excess heat. Coastal ecosystems shifted as heat stress overwhelmed cool-water kelp, seagrass, and coral habitats. The resulting habitat conversions and effects from food web alterations led to disruptions in the fishing, aquaculture, and tourism industries. HOW LIKELY IS IT? In 2013-2016 the Northeast Pacific Ocean "Blob" produced: seabird and marine mammal die-offs due to reduced prey availability, fishery closures associated with harmful algal blooms, and declines in estuarine seagrass. The frequency and intensity of marine heatwaves is increasing relative to historical baselines. They have occurred along all U.S. coasts, and estuary temperature records show warm anomalies at the same time as offshore heatwaves. It is likely that already-seen emergency responses such as changes to fishery season and catch limits, marketing of newly available or abundant seafood species, or moving or harvesting aquaculture species before heat stress, will continue to be needed. Eventually environmental management must shift from responding to events and adapt to new prevailing temperatures. OPPORTUNITIES AND CHALLENGES Warmer water or longer warm seasons may improve conditions for some species and boost some types of aquaculture. Scientists are examining recruitment failures that are associated with above average temperature. Heatwaves threaten the availability of culturally important foods, especially for indigenous populations. Additional research is needed to understand how heat propagates from the sea and upstream in estuaries. Assessment 1 3-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- POLICY CONTEXT AND QUESTIONS Management must recognize that gradual water warming will be punctuated by heatwaves that can push systems past thresholds. While short-duration events may function as sporadic shocks to coastal ecosystems from which recovery is possible, longer lasting events will speed already-occurring ecosystem transitions. Coastal managers will need to evaluate the cost-effectiveness and durability of temperature interventions such as habitat restoration and selective breeding and cultivation of heat-resilient genotypes to resist ecological transitions. Various regulatory and policy tools, such as threshold triggers or time/duration/frequency components in permits might help meet water quality goals. Nevertheless, continued reductions to other stressors are needed to increase resiliency to extreme oceanic events. Heatwaves and ocean warming may also change the ultimate attainability of water quality goals. This scenario connects to sustainability goals for: zero hunger decent work and economic growth responsible consumption and production life below water. SELECTED REFERENCES Harvey, B. P., Marshall. K. E., Harley, C. D. G., & Russell, B. D. (2022). Predicting responses to marine heatwaves using functional traits. Trends in ecology & evolution, 37(1), 20-29. https://doi.ora/10.1016/i.tree.2021.09.003 Smale, D.A., Wernberg, T., Oliver, E.C.J, et al. Marine heatwaves threaten global biodiversity and the provision of ecosystem services. Nat. Clim. Chang. 9, 306-312 (2019). https://doi.ora/10.1038/s41558-019-0412-l Pershing, A.J., K.E. Mills, A.M. Dayton, B.S. Franklin, and B.T. Kennedy. 2018. Evidence for adaptation from the 2016 marine heatwave in the Northwest Atlantic Ocean. Oceanography 31 (21:152-161, https://doi.Org/l 0.5670/oceanoa.2018.213 Change in annual cumulative intensity of marine heatwaves in the U.S., 1982-2023 (https://www.epa.aov/climate-indicators/climate- chanae-indicators-marine-heat-waves). Cumulative intensity is presented in degree days, which is equal to marine heatwave intensity multiplied by duration. The red shaded areas experienced an increase in marine heatwave cumulative intensity, (Data Source: NOAA) ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Rising seas and floods threaten homes and businesses, and consequently community viability. Adopting floating building technologies would avoid damages and enable continued investment in these places. They can be an alternative to relocation and keep neighborhoods intact. TURNING TO FLOATING BUILDINGS COASTAL FUTURE HOW DOES IT LOOK? Increasing depths and frequency of coastal flooding were making parts of communities unviable. Repeatedly attending to flood and storm damages became unavoidable. Many residents and businesses chose to relocate; however, some saw floating and amphibious structures as a way to preserve their real estate investments and remain in their neighborhoods. Communities embraced these buildings to sustain flood-prone areas and establish new developable spaces. Now, residential and commercial uses are routinely found in floating and amphibious structures that safely rise above the increasingly frequent coastal floods. HOW DID IT HAPPEN? Floating structures (located over water) and amphibious structures (located on land) rely on a buoyant foundation and anchoring system. Enterprising marinas began offering slips for floating structures, with the occupiable structure commonly built atop a barge or timber foundation. Unlike houseboats, floating structures had no means of self-propulsion and are semi-permanently anchored. Some floating and amphibious structures used hulls attached to stabilizing pylons that allow for vertical movement in-place. Most were 1-3 stories, reflecting a delicate balance of buoyancy, stability, space layout, and even furniture placement. Flexible, extra-long piping connected the structures to on-land utility networks by running below access piers. Wastewater was typically stored in holding tanks and pumped from the structure to the on-land utility network. HOW LIKELY iS IT? While communities are very likely to explore adaptation options for flood-prone locations or seek to offset a lack of developable land, floating and amphibious structures are unlikely to be widely adopted due to cost, complexity, and site constraints. Floating and amphibious structures are typically located in areas with some protection from waves (e.g., sheltered marinas, rivers), limiting where they can be used. In areas where amphibious structures are suitable, home- and businessowners are likely to be more comfortable with conventional fixed, elevated structures. In Europe, floating structures have been developed as planned overwater neighborhoods to reduce project construction and maintenance costs, whereas amphibious structures are less utilized. In the U.S., where existing floating structures are generally located in marinas, it is unlikely that communities will expand into planned new neighborhoods. Floating casinos (so-called "riverboats") are familiar in the U.S. There is currently a limited market for cruise ship apartments and floating and amphibious homes and resorts which are oriented toward the luxury buyer, and it is unlikely that these setups will be affordable options. This combination of cost and risk is thought to make it likely that individuals will opt for more conventional, affordable options in established, safer areas. The strategy may have limited potential in single projects and commercial uses. Assessment 1 4-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES In communities with limited developable land, floating structures offer opportunities to accommodate sea level rise within existing neighborhoods. Residents with strong community ties could remain although their home and neighborhood would be radically reconfigured. As with boats, floating structures will need regular hull maintenance. Similarly, indoor dampness, mold, and mildew will need attention. Structures may safely float but access in and out will be affected when roads and neighborhoods are flooded. Floating and amphibious structures connect to on-land utility networks. Flood and storm damage (including on land) may affect services, including the ability to pump wastewater. A strong concern is the accidental discharge of untreated wastewater into waterways. Buildings rise with floodwaters and rock with waves, so extreme storms, high winds, or large waves may lead to structural and infrastructure damages or failure. Occupants who stay during storms may be at risk. Owners could find that insurance is unavailable. POLICY CONTEXT AND QUESTIONS Land and water use conflicts involving recreation, public access, and scenic value interests are likely to stymie development in high water use areas. Impacts to aquatic life must also be considered, particularly for floating structures that affect light, wave energy, or bottom habitats. As floating and amphibious structures are necessarily within floodplains or regulatory floodways, their adoption requires a reimagining of how communities conceive of flood risk. Communities and states may find that floating structures stretch the limits of existing building codes and land use regulations, increasing the regulatory hurdles and cost of construction. Further, states and communities may find that wastewater management and the risk of accidental discharges are counter to established water quality and public health standards and regulations. This scenario connects to sustainability goals for: clean water and sanitation decent work and economic growth sustainable cities and communities. Floating homes in Amsterdam. SELECTED REFERENCES Penning-Rowseil, Edmund. Floating architecture in the landscape: climate change adaptation ideas, opportunities and challenges. Landscape Research 45, no. 4 (2020): 395-411. https://www.tandfonline.com/doi/full/10.1080/01426397.2Q19.1694881 Ontwikkelingscombinatie Waterbuurt West and Projectbureau IJburg of the Municipality of Amsterdam. Floating Amsterdam: The development of IJbura's Waterbuurf. 2012. Boiten raadgevende ingeniuers & Factor Architecten. Project review: Floating Homes 'De Gouden Kust,' Maasbommel, the Netherlands, 1998-2005. 2011. ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Sea level rise with more frequent and severe storms are leading to an increasingly loud call for coastal engineering to prevent flooding and erosion. Accessing and using beaches, piers, marinas, and ramps outside of protective works can become difficult, and these facilities will remain exposed to destructive storms. LOSING WATERFRONT ACCESS COASTAL FUTURE HOW DOES IT LOOK? Fishing, boating, sunbathing, swimming, and other recreation activities were an undeniable draw to coastal places. As threats from sea level rise and worsening coastal storms began accumulating, shoreline communities turned more and more to coastal engineering to stay viable. Walls, levees, dikes, and armoring were effective at stopping flooding and erosion. However, this security came at the expense of the beaches, swimming areas, piers, boat ramps and marinas that were left unprotected. They were out of sight, difficult to access, and eventually damaged or squeezed out between water side inundation and static land side structures. HOW DiD IT HAPPEN? Coastal communities' main desires were to preserve homes and businesses and stabilize their shorelines. They protected development on one side of an armored line. Sometimes strips of natural landscape (e.g., beach fills, living shorelines) were employed as a buffer on the water side of the line. Without continual maintenance the artificial beaches and wetland buffers were squeezed out against the walls and levees. Ocean beaches were more likely to be maintained in front of a seawall than estuarine salt marsh in front of a floodwall because beaches were fundamental in the seaside communities. In some cases, communities used networks of engineered structures, creating protective rings with combinations of levees, floodwalls, seawalls, armored dunes, and sea gates. The structures had substantial height to protect from extreme storms. These protective infrastructure rings became barriers to direct water access. Piers, boat ramps, and marinas were stranded and forgotten outside of these rings. Some places had walkways atop levees and seawalls to preserve viewscapes, otherwise the shoreline stayed out of sight. Plentiful access points were often provided for ocean beaches, but access to the bayside shoreline was intermittent and direct access to the water may have been unavailable or required passing over walls, down bulkheads, or across revetments. HOW LIKELY IS IT? Armoring has been a standard response to coastal hazards for centuries, in part because coastal roadways and other coastal infrastructure were historically built without sea level rise in mind. Despite the high costs required for the installation and maintenance of engineered structures, communities have continued to rely on armoring to protect existing development. While there is some discourse about nature-based solutions, the evidence shows that shoreline communities want (and are getting) levees, walls, tide gates, and so-called "dunes" that are vegetated sand veneers over steel or concrete. In recent decades, some coastal states have begun to weigh the impacts of armoring against the potential loss Assessment 1 5-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- of public access to the shoreline. In part because of this concern, there has been pressure for sta tes to encourage alternatives such as living shorelines, managed relocation, and retreat. However, because the threat of sea level rise to public infrastructure and private property is intensifying, and so many concept plans for perimeter protection are on the drawing boards, it is very likely that use of levees and walls will be widespread in densely populated areas, perhaps coupled with some nature-based solutions. While many communities may attempt to preserve views with elevated boardwalks and waterfront parks, it is very likely that easy public access to the water itself will be restricted, difficult or lostespecially on highly developed estuarine shorelines. OPPORTUNITIES AND CHALLENGES Alternative adaptation measures, such as acquisition or rolling easements can protect public access to the shoreline. Because armored shoreline structures may need to be rebuilt higher over time or may need to expand into adjacent spaces, communities may come to regard public access as a transitory amenity. Coastal communities may see decreased tourism if they are unable to maintain access ways to public recreation. For communities that draw their identity from their proximity and access to coastal resources, this change will be profound. Narrow "living shorelines" with no ability to migrate inland will have short lifespans unless regularly raised and renewed. Breakwaters that are commonly co-installed with living shorelines will become submerged and can be a swimming or boating hazard unless they are tended to as well. POLICY CONTEXT AND QUESTIONS As sea level rise and erosion continue on, more communities may be drawn to invest in shoreline engineering to protect existing development. However, engineering solutions can negatively impact public access. Stronger policies and mechanisms may be needed, including strategies like rolling easements. The loss of access to and use of beaches, piers, and marinas, also raises concerns that the populations which use these public resources may not be the same segment of the public that benefits from the protection of shoreline investments. Maintaining recreation in and on the water is among the reasons for the Clean Water Act, which states a national goal that water quality will provide for those activities. This scenario connects to sustainability goals for: sustainable cities and communities. SELECTED REFERENCES Gittman, Rachel et al. (2015). Engineering away our ngfurgl defenses: gn gnglvsis of shoreline hordening in the US. Frontiers in Ecology and the Environment 13, 6 (2023): 301-307 Hgwgii Depgrtment of Lond grid Ngfurgl Resources. Lorid Division. Howgii Coosfgl Lgnds Progrom. Hawaii Coastal Erosion Management Plan. 2013. US Army Corps of Engineers, Philodelphig District. New Jersey Back Bays Coastal Storm Risk Management Draft Integrated Feasibility Report and Tier I Environmental Impact Statement. New Jersey Bgck Bgys Study, 2021. The U.S. Army Corps of Engineers' Philadelphia District constructs two new sections of a seawall and rebuilds portions of the Atlantic City boardwalk along the Absecon Inlet in New Jersey following coastal storm events. (Tim Boyle, U.S. Army Corps of Engineers). ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS In much of the country warmer air and water temperature are allowing boating to begin earlier in the spring, and go longer into the fail. An extended boating season will lead to greater environmental impacts, and bring new ones as boats become a presence in months when they had been absent. EXTENDING THE BOATING SEASON COASTAL FUTURE HOW DOES IT LOOK? As global air and water temperature kept warming, the shoulder seasons for boating kept extending. Whereas in much of the country Memorial Day and Labor Day were previously cultural markers opening and closing the season, now boating starts earlier and ends later. This led to further common boating impacts as a result of more days on the water. New ecological problems also emerged as boats became a presence in what had been the off season. HOW DID IT HAPPEN? Boaters continued to operate earlier in the year as the climate continued warming. Likewise, they stayed on the water later in the fall. The boating season grew significantly longer than the three and a half months it had been from late May to early September. Increasing the time that boaters and fishers, plus tour boats and seasonal ferries, were on the water simply added more chances for routine impact from moorings, maintenance, trash and noise. Fuel spills, plus sewage and other discharges such as graywater and bilgewater, increased proportionally. Shoreline erosion and anchoring impacts did too. Management strategies for familiar impacts like seagrass damage, invasive species or interactions with marine mammals needed more education and monitoring during longer seasons. New impacts also emerged from extended marina operations. Fishing outside of traditional dates added pressures on species and carried the risk of exceeding annual fishery allotments or activity in closed seasons. There was greater human presence during bird migration and breeding seasons too. HOW LIKELY IS IT? In areas that have a traditional boating season of Memorial Day to Labor Day, a gradual extension of the boating season is likely. Any extension to the boating season makes it likely that associated ecological impacts to habitat and water quality and direct impacts to fish, migratory birds, and seagrass will be seen. Other factors that may affect outcomes include whether more people will own boats if the season is longer. Assessment 1 6-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- OPPORTUNITIES AND CHALLENGES A longer season can place additional burdens on regulatory and safety agencies, and waterfront municipalities. A longer season can bring positive effects for tourism and the marine trades. Greater excise tax revenue may be available to fund conservation activities. POLICY CONTEXT AND QUESTIONS Fishery management may need to adjust quotas in recognition of longer seasons or for the temperature driven changes to species presence. Further use of no-discharge zones which are designated areas where the discharge of both treated and untreated sewage from vessels is prohibited can be one strategy when waters require additional protection. Having pumpout stations where sewage holding tanks may be emptied is an accompanying technique. This scenario connects to sustainability goals for: decent work and economic growth life below water. SELECTED REFERENCES Carreno, A. & Lloret, J. (2021). Environmental Impacts of Increasing Leisure Boating Activity in Mediterranean Coastal Waters. Ocean & Coastal Management, 209. https://doi.ora/] 0.1016/i.ocecoaman.2021.105693 About the Clean Boating Act (CBA) https://www.epa.aov/vessels-marinas-and-ports/about-clean-boatina-act-cba A Recreational Boater's Guide to Vessel Sewage https://www.epa.aov/sites/default/files/2021- 06/documents/a recreational boaters guide to vessel sewaae.pdf ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Earth systems monitoring and future conditions modeling yield a torrent of data about coastal conditions. Alas it is beyond what humans can comprehend and act on in real time. Artificial intelligence systems are extending human capacity, although turning to Al introduces technology risk. TURNING TO ARTIFICIAL INTELLIGENCE COASTAL FUTURE HOW DOES IT LOOK? Environmental changes brought a myriad of challenges to coastal management. Novel situations emerged and long-standing problems were exacerbated. Stressors as diverse as water temperature, precipitation and sea level rise, increased the value of artificial intelligence technology that integrated multiplying data streams, helped with scenario analysis, predicted extreme events, and analyzed monitoring results. Al became more and more important for identifying risks and implementing responses. HOW DID IT HAPPEN? Machine learning is a type of Al that recognizes patterns in data, reduces time from data collection to forecasts, can increase accuracy by using more data than models (or humans) can, and synthesizes information to fill data gaps. Generative Al uses neural networks to create text or image content. In the mid-2020s this technology became mainstream through search and chat functions that fed it user prompts. Users became familiar with confabulations (colloquially known as "hallucina tions") in which an Al synthesizes wholly fictional responses. Because Als were trained on enormous datasets, they inherited the characteristics and biases of their input. For example, environmental models had better representation of populated areas with rich data collection than other places. As Al capability grew and managers became confident, processes were automated. Issuing weather outlooks and warnings, rerouting shipping around marine mammals, anticipating and managing reservoir levels, opening and closing tide gates, summoning law enforcement, controlling autonomous vehicles and ships, and numerous routine, mundane and arcane tasks were taken over by Al and automation. Of course it was nearly impossible to understand how they worked. HOW LIKELY IS II? Al systems are already playing a role in science and management. EPA scientists have been using machine learning for quite some time and neural networks are common in the sciences. U.S. Forest Service used Al to help deploy firefighting resources. The Department of Commerce's Artificial Intelligence Al Use Case Inventory - 2022 (https://ai.aov/ai-use- cases/), related examples of how NOAA used Al for: analyzing acoustic data to detect whales and other marine mammals, improving drought outlooks, classifying land cover, preparing for coral bleaching, identifying phytoplankton, detecting fog, forecasting severe wind, hail and tornadoes, and making wave observations, among other uses. It is very likely that Al will have an even larger role in coastal management as its capabilities increase and users gain confidence. NIST Al 600-1. Artificial Intelligence Risk Management Framework: Generative Artificial Intelligence Profile 2.2. Confabulation "Confabulation" refers to a phenomenon in which [Al] systems generate and confidently present erroneous or false content in response to prompts.... Confabulations are a natural result of the way generative models are designed: they generate outputs that approximate the statistical distribution of their training data.... While such statistical prediction can produce factually accurate and consistent outputs, it can also produce outputs that are factually inaccurate or internally inconsistent. This dynamic is particularly relevant when it comes to open-ended prompts for long-form responses and in domains which require highly contextual and/or domain expertise.... Risks from confabulations may arise when users believe false content - often due to the confident nature of the response - leading users to act upon or promote the false information. Assessment 1 7-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- It is very likely that Al systems will synthesize data streams and then implement procedures that have environmental outcomes. While it is desirable to have humans in the loop, humans won't always have the ability to apprehend the data or second guess an Al system, or will have lower skepticism about systems that have always performed well. Over time and with wide use, errors and confabulations from Al are very likely. Risks will need to be continually monitored and mitigated. OPPORTUNITIES AND CHALLENGES Al can master the volume and types of data from satellites, instruments, drones and models that are too numerous for humans to handle in real time. Al is trained on pre-existing data, so results are most accurate when the current condition is representative of the data. Using Al to supplement human skills and abilities can enlarge participation in the environmental workforce. Al models are expensive to both develop and run, with high costs for research and training as well as high energy use. POLICY CONTEXT AND QUESTIONS Risk management will be essential and there is a high need for systems around the systems. Coastal managers are going to have to decide how much autonomy for what types of decisions they will grant to Al and automation. There is growing in terest in regulations to govern Al perils. This scenario connects to sustainability goals for: decent work and economic growth industry, innovation, and infrastructure sustainable cities and communities responsible consumption and production life on ^ vas^ Qf platforms and data streams keep tabs on conditions and provides critical iQr|d. information. https://www.noaa.aov/exDlainers/monitorina-our-chanaina-world-from-land-sea-and-skv SELECTED REFERENCES U.S. Government Accountability Office (2023). Artificial Intelligence in Natural Hazard Modeling: Severe Storms, Hurricanes, Floods, and Wildfires, https://www.aao.aov/products/aao-24-106213 The United Nations Educational, Scientific and Cultural Organization (2022). Fighting Climate Change with the Al for the Planet Alliance, https://www.unesco.ora/en/articles/fiahtina-climate-chanae-ai-planet-alliance National Institute of Standards and Technology (2024). Artificial Intelligence Risk Management Framework: Generative Artificial Intelligence Profile. U.S. Department of Commerce, https://www.nist.aov/itl/ai-risk-manaaement-framework OMB M24-10. Advancing Governance, Innovation, and Risk Management for Agency Use of Artificial Intelligence. https://www.whitehouse.aov/omb/information-for-aaencies/memoranda/ air gap sensor continuously operating reference station PORTS0 visibility sensor water level gauge buoys: ocean chemistry wave sensors water temperature gauge meteorological sensors monitoring ATON mounted acoustic doppler current profiler bottom mounted acoustic doppler current profiler glider or autonomous underwater vehicle ------- CLIMATE READY ESTUARIES xvEPA WHY THIS MATTERS Storms and sea level rise combine to bring more frequent costly events. As damages and repair bills accumulate, eventually some will abandon their houses. As they depart they will leave much behindin proven risky places. It will fall to local government to clean up and restore these abandoned sites. RESTORING ABANDONED SITES COASTAL FUTURE HOW DOES IT LOOK? Sea level rise led to more frequent high tide flooding and worsened the impacts of coastal storms. The endless cycle of floods, storms, and repairs became financially and emotionally burdensome for many coastal residents. Eventually, property owners began making ad hoc decisions to relocate. Abandoned property deteriorated and led to adverse environmental impacts. HOW DiD IT HAPPEN? Although residents of at-risk homes hoped for protection, after damage had already occurred many were interested in buyouts. Yet it was difficult to coordinate and operate buyout programs even when communities had funds available. Without any assurance that their homes would be bought out and facing a long process regardless: unplanned retreat from hazardous areas occurred whenever owners became unwilling or unable to bear the repeated repairs and accumulating costs of recovering. Shouldering the cost became even more of a personal burden when private insurance companies withdrew from the coastal market. Some states tried to fill the insurance gap, although policies were expensive due to small risk pools and high-risk property. Responsibility for cleanup and the cost of remediating public nuisance properties fell to health departments and environmental agencies. Abandoned properties presented public health hazards due to septic systems, fuel tanks, discarded pesticides, household chemicals, flood damaged vehicles, or asbestos building materials. Keeping building debris from entering waterways posed further concerns. Attention to these matters was not a priority in lower-resourced communities. The presence of vacant properties and derelict structures frequently had a negative effect on other residents' desire to stay, perpetuating a cycle of abandonment. When cleanups did occur, there was an opportunity for environmental restoration in lieu of reoccupation at these demonstrated dangerous locations. However, land trusts and wildlife agencies had little interest in acquiring titles and spending resources to restore habitat at small, random, dispersed sites. HOW LIKELY IS IT? It is very likely that coastal risks will increase in response to sea level rise and changes in extreme weather patterns. The U.S. Congressional Budget Office estimates that homes outside of PEMA-designated Special Flood Hazard Areas will account for approximately 40-50 percent of expected annual flood damage under a 2050 projection, making it likely that many affected residents are unaware of flood risk, will not carry optional flood insurance, and will be less resilient to flood damage. Additionally, insurance companies are withdrawing from increasingly hazardous coastal areas, leaving residents to bear the full risk of storms. Assessment 1 8-2025 Foreseeing Coastal Change To Strategically Guide Adaptation, EPA 840R25001 ------- Some federal agencies offer property buyout programs, although historically projects have typically been small, targeting only a few individual properties. It is very unlikely that everyone who becomes interested in a buyout will be accommodated. Jurisdictions in higher-income and denser counties are more likely to conduct buyouts. It is about an even chance that rural coastal areas will see some abandonment. Abandonment is not a novel reaction: abandoned buildings are easily found in the U.S., and this country has a notable number of ghost towns. Since property in good condition is very unlikely to be abandoned, where there are abandoned sites they are very likely to pose environmental problems, become nuisances, and need cleanup and demolition. Without a process to structure an ownership transfer, abandoned property is very likely to remain neglected. Even if a buyout acquisition is completed, land- use analysis of past FEMA-funded buyout sites suggests that ecological restoration occurs infrequently. OPPORTUNITIES AND CHALLENGES Federal programs for buyouts typically require the permanent conversion of buyout sites to open space or other floodplain compatible uses. Restoration of small, dispersed sites can still produce meaningful ecological benefits (i.e., wildlife habitat, wildlife corridors and linkages, flood storage). Future buyouts in the same area offer the potential to restore larger tracts. POLICY CONTEXT AND QUESTIONS Relocation from coastal hazards in the U.S. is primarily facilitated by post-disaster federal- and state-funded buyout programs, sometimes with local match, which results in an ad hoc approach that is difficult to predict. Restoration and reuse of buyout sites may challenge less affluent communities, where acquiring, restoring and maintaining land may be perceived as a burden. Disaster victims will not be alone in making decisions to withdraw from coastal risk. Local governments will assess their legal obligation to maintain, repair, and upgrade vulnerable roads and infrastructure. This could be another push factor. Pre-disaster planning, which could include targeted or wholesale relocation, can help create a transparent dialogue between local governments and residents to ultimately limit outmigration, encourage local resettlement where appropriate, and maintain a sense of community. This scenario connects to sustainability goals for: no poverty good health and well-being reduced inequalities sustainable cities and communities life below water life on land. SELECTED REFERENCES EPA Toolkit about Abandoned Mobile Homes, https://www.epa.aov/smm/toolkit-about-abandoned-mobile-homes Congressional Research Service. 2024. Floodplain Buyouts: Federal Funding for Property Acquisition. https://crsreports.conaress.aov/product/pdf/IN/INl 1911 Mach, K. J., Kraan, C. M., Hino, M., Siders, A. R., Johnston, E. M., & Field, C. B. (2019). Managed retreat through voluntary buyouts of flood-prone properties. Science Advances, 5(10). Anurodhg Mukherji, Ke'Ziygh Willigmson, Koyode Nelson Adeniji, Milleo Meghgn, Scott Curtis, Bello Sgrding, 2024. Buyouts in the Corolinos: Pre & Post buyout perspectives of public officiols gnd community leoders. International Journal of Disaster Risk Reduction, Volume 113. https://doi.ora/10.1016/i.iidrr.2024.104906. Volunteers help after a hurricane. FEMA/Marvin Nauman ------- |