Adaptation through design Coastal Ecological Passage (CEP) as an innovative nature-based defense to tackle rising sea level

Abstract

Sea level rise(SLR) due to climate change is and will continue altering the world's coasts, which are the most densely populated and economically active areas on earth and home to highly valuable ecosystems. Today, It is too late to make mitigation the primary strategy for defending against climate change, and enhancing urban resilience has become the focus of adaptation strategies. In the meantime, design-based disaster response must be considered from coastline defense to inland adaptation to achieve adequate protection and adaptation. The theory of metropolitan "resilience districts"1 proposed by Alan M. Berger offers the appropriate decision-making unit (DMU) to analyze, design, and implement fair resilience strategies. However, cities to use this theory for their own resilience policies require a further understanding of strategies to build innovative "coastal defense zone "and "borders of districts" that form the structure of the urban adaptation framework.

This paper argues that the theory of 'ecological coastal passages(CEP)' offers a masterplan design support tool that provides planning & design guidelines for the implementation of 'resilience districts' in the different scales that aid in improving the region's resilience tackle hazards by sea-level rise.

This analysis details a design strategy on the macro scale, a master plan of 'CEP's network' to identify a 'resilience districts' framework for the city of New York. The research culminates with a generalizable urban planning and design framework for protecting critical infrastructure, 'thickening' regional soft systems, and turning the coastal delta metropolitan area into a resilient sponge. The overall theme emphasizes landscape as a critical public safety service.

1. A review of contemporary coastal adaptation to SLR: from mitigation to resilience

Articles with keywords" Coastal area" and" sea-level rise" on WOS are over five thousand in total, but most of them are not from spatial design fields. Through the quantitative analysis of all the above papers, In the figure of the keyword timeline, it can be seen that in recent years, the attitude towards coastal areas was from "management" by 2004, "reconstruction" by 2007, to "resilience "by 2016.

From grey to hybrid: coastal defense

The Contemporary coastal adaptation has experienced two stages: coastline defense upgrading and design framework from the coastline to inland. In general, from mitigation to resilience. Two types of gray infrastructure are built to protect coastal areas from marine flooding: passive and active defenses. These are designed for natural hazards of a certain magnitude, ensuring greater protection within a capacity, which means artificial defense structures could not function if the intensities of natural hazards were beyond their thresholds2. Therefore, the "nature-based" strategies are researched to replace the traditional "hard" approaches over the last three decades: wetlands, mangroves, coral and oyster reefs, etc. However, the hybrid way has attracted more attention worldwide as there are still some weaknesses of "nature-based" solutions3. What is more, dealing with the sea level rise still needs to prevent land subsidence. The Sponge City Theory toolkit for rain-flooding management can mitigate the land subsidence, such as rain gardens, sink green area, seepage pavement, etc4.

From the coastline to inland

Articles with keywords "Coastal planning" and "Sea-level rise" on WOS are only 106 in total, while 2012 was an inflection point for research in this field where the number of studies increased gradually. The massive increase in research after 2012 is due to some global climate catastrophes that have risen significantly in recent years. The representative Sandy Hurricane disaster-hit many countries in 2012-2013 and affected 24 states in the United States. Many coastal metropolises were severely affected. After the disasters, professional practitioners realized that design must be considered from coastline to inland to achieve adequate protection and adaptation. Therefore, many studies and competitions were initiated, such as Rebuild by design. Many frameworks for coastal adaptation to these Impacts have been proposed. In these theories, Ecological planning has proven to be effective in improving urban resilience. The landscape of the Toms River-Barnegat Bay ecosystem in New Jersey is a proof-of-concept5, showing that collaborative design can improve the ability of shore regions to recover from storms and sea-level rise if it uses a broad concept of the shore's ecological and geomorphological structures. "Resilience districts" Theory offers the appropriate decision-making unit (DMU) to analyze, design, and implement fair resilience strategies. Each of these districts is operated by deploying a spatial strategy that responds directly to its particular set of challenges1.

In conclusion,

- compared to the traditional grey coastal defense, ecological collaborative design is proven to be effective in improving the ability of shore regions in many regions to recover from storms and sea-level rise;

- studies of Coastal protection are multidisciplinary, including coastal defense engineering, ecology, landscape design, etc. are mostly concentrated in their own fields, and the study of integrating multi-field research in spatial design still needs to be studied; - The review of contemporary coastal adaptation to SLR shows that there is a lack of a master planning design support tool that can be generalized on similar areas, providing planning and design guidelines for the implementation of adaptation design that aid in improving region's resilience to tackle hazards by sea-level rise. This research aims at filling in this gap.

2. A proposed 'ecological coastal passages' network for the City of New York

Coastal ecological passage is a narrow, linear (or near-linear) functional space that connects different spaces in series, distinguishing and linking different "Resilience zones" 1, also facilitating movements of animals and dispersal of plants and other organisms. The network of coastal ecological passages contains four different types of passages.

The theory of 'ecological coastal passages' design strategy is articulated from three parts,

1. at the micro-level a collection of toolboxes, divided into flooding and coastal management, including the sponge city theory, etc;
2. at the macro level, a master plan of 'CEP's network' to identify an effective 'resilience districts' framework;
3. at the meso-neighborhood scale, combining macro and micro experiences, design on the pilot areas will be conducted in detail in accordance with four different CEPs by applying the theory of design-driven research.

Macroscale: A proposed 'ecological coastal passages' network

This part details a macro-level design approach for the CEP network, using New York as an example. The CEP network combines potential ecological and geomorphological structures with existing spatial characteristics at the macro level (Figure1). Connected potentially fragmented open green spaces and based on the existing urban morphology, the CEP forms a system of buffers to the transportation system and critical infrastructure. Under the premise that priority can be given to protecting critical infrastructure and roads after a disaster, ecological passages can be exploited to absorb the impacts of floods and storm surges, enhancing the city's resilience and capacity to withstand disasters.

Design Phases

A. Urban Vulnerability Points/Areas at risk: Use urban morphology and urban vulnerability analysis to map vital infrastructures and points to 'protect' the city from the hazards.

Infrastructures, including Transportation and energy supplies, are the vital baseline for post-disaster assistance and reconstruction and are also fragile elements. Those are the primary objectives of the CEP network to protect by providing buffer zones. While wastewater treatment facilities are essential to treating the watershed's wastewater and stormwater before it flows into the bay, they can pose a threat if flooded. Ten of the city's fourteen wastewater treatment plants released partially treated or untreated sewage into the water during Sandy, and nearly half of the pumping stations keeping the city's stormwater and sewage systems moving were out of service due to power failures. According to the Facility Registry Service (FRS) datasets from the Environmental Protection Agency, wastewater, power plants, hazardous waste sites, pollutant discharge sites, bulk storage facilities, toxic chemical sites are taken into consideration, such as Jamaica Bay Water Pollution Control Plant, Motiva Long Island Terminal,Allied Aviation Fueling Facility,etc.

The transportation infrastructure includes major intra-city arterial roads, inter-city highways, railway tracks, etc. Transportation ecological passage should be built to increase the resiliency of train lines and roadways to prevent negative economic impacts to the communities that rely on them and ensure evacuation routes to coastal locations, including the Rockaway Peninsula, remain accessible prior to a severe storm. The possible actions are combing the vegetation on both sides, raising the road height, or setting green-gray embankments on both sides of the road to protect the transportation infrastructure.

The vital transportation infrastructure map collation's sources are from New York State National Geospatial Data Assets (NGDA), NYC Metropolitan Transportation Authority (MTA), Open Street Maps (existing runways), Regional Planning Association (proposed runways), Department of Urban Planning (NYCDCP).

Thus, "Map of Urban Vulnerability Points/Areas at risk" can be identified from transportation infrastructure, critical (energy plants, medical institutions, food storage, signal stations), hazardous infrastructure (wastewater treatment plants, power generation facilities, and fields of oil storage tanks), vulnerable neighbors (poverty, vehicle access, number of residents with disabilities, English fluency, prevalence of children and seniors).

B. Projected Hazards' risk

Understanding the probability and potential impacts of future flooding can provide policymakers, planners, and designers with a projection of a probabilistic future that encourages actionable adaptive design strategies, despite indeterminacy. I take the projected risk of storm surge, tidal cycles, flooding. Data is from NYC Flood Hazard Mapper.

• for example, where one should park a car so that it is not impacted by a hurricane
• Encourage planned retreat and ecological restoration of higher risk areas that are likely to be permanently inundated

C. Urban morphology

Urban morphology: linear spaces (roads, etc.), scattered green areas, fragmented open spaces, topography, etc.

The construction of the CEP network leverages the city's existing linear spaces (roads, etc.), fragmented green spaces, scattered open spaces, topography, and natural ecosystems to reduce the reliance on hard infrastructure and human intervention for a less costly and low-impact-development CEP framework. Figure 2 shows a scheme of proposed ecological coastal passages.

Four types of ecological passages

• 'Transportation ecological passages' enhance evacuation potential and the ability of vulnerable populations to reach health care centers during severe storms or disruptions and transfer density to less vulnerable areas;

• "coastal defense passages" are hybrid coastal defenses of nature-based coastal revetment and protective constructions(walls, dams, dikes);
• 'River ecological passages' reconceive the shore connecting the beach to the inland;
• ‘Thick zone edge ecological passages’ combine hard and soft infrastructure, leveraging opportunities that capitalize on existing linear features such as highways and rail corridors. Coupled with hard structures (walls, dams, dikes, and stairs), soft protective infrastructure such as earthworks (terraces, mounds, and berms) would be built parallel to the coastline;

Proposed resilience districts

Once the network of CEPs has been identified, resilience districts will be formed accordingly. Figure 3 shows the tiered resilience districts in New York.

Once the resilience districts have been identified, they will be sub-divided into three distinct zones. (Figure4)

Down Zone

Down zones, referring to prevention and retreat, are the low-lying area in each resilience district with the greatest exposure to coastal flooding. Resilience projects in this zone should protect critical infrastructure using walls, berms, and levees while expanding the hydrological capacity of the district using engineered wetlands and other forms of soft infrastructure. This zone will probably see the highest level of expenditure.

To define these boundaries of the Down zone, this paper proposed “Coastal defense passages,” River ecological passages,” and ”Transportation ecological passages” to serve as the boundaries.

Up Zone

Up zone, referring to the safe zone, encompasses most of the resilience district's higher elevation. Though the direct effects of flooding are less prevalent here, indirect effects of regional infrastructure failure could still inflict significant losses. The transfer of development rights from the down zone can help increase density and provide real estate options for down-zone residents who wish to relocate within reach of critical local resources such as schools and hospitals.

To define these boundaries of Up zone, "Transportation ecological passages" and "Zone edge ecological passages" are proposed to serve as boundaries.

Transition Zone

The transition zone is lying in between acts as a staging ground for the continual evolution of the resilience district. Over time, the more exposed outer edge of the transition zone will become the new urban waterfront.

To define these boundaries of the Transition zone, "Transportation ecological passages" and "Thick zone edge ecological passages" are proposed to serve as boundaries.

Proposed ecological resilience districts

Combined with the toolbox at the micro-level, different GI approaches are used for different points on the CEP. Figure 5 shows the master plan of the final CEP network in New York City.

3. Conclusion

The review of contemporary coastal adaptation to SLR shows a lack of a master planning design support tool that can be generalized on similar areas, providing planning and design guidelines for the implementation of adaptation design that improves the region's resilience to tackle hazards brought by sea-level rise. This research filled this gap.

Compared to the traditional grey coastal defense, ecological collaborative design is proven to improve the ability of shore regions in many regions to recover from storms and sea-level rise.

The theory of metropolitan "resilience districts" 1 offers the appropriate decision-making unit (DMU) to analyze, design, and implement fair resilience strategies. However, how to scientifically set the boundaries of the resilience districts and guide the implementation of the design of the city-scale? The theory of Ecological coastal passages strategy can be a potential answer.