+ A Damage Allowance Framework to Support the Appraisal of Coastal Flood Mitigation Strategies

D.J. Rasmussen, Princeton University

Rising mean sea levels are already magnifying the frequency and severity of extreme coastal water level (EWL) events that lead to coastal flood damages. As such, new planning tools and metrics are needed to manage this threat. The so-called “flood allowance” (e.g., Hunter, 2012; Buchanan et al., 2016) is the vertical distance by which something needs to be adjusted in order to ensure that the average number of EWL events for a given instance in time remains constant under SLR. For example, a residential structure elevated by the flood allowance would, on average, experience the same frequency of EWL events with an arbitrary amount of SLR as it would without. Traditional flood allowances only consider purely physical EWL metrics (e.g., the 100-yr flood) and therefore give no information regarding the damages caused by such physical hazards themselves. As such, they may be limited when appraising various solutions for managing damages from EWL events and SLR. Here, we develop a damage allowance framework for determining the design of flood mitigation strategies needed to maintain the current expected annual damage from EWL events under SLR and apply it to New York City. Expected annual damages are estimated using 1) an extreme value distribution of EWLs constructed from a long-term record of tide gauge data at the Battery in lower Manhattan and 2) an EWL damage function for New York City that relates EWL inundation to financial damages. We consider the flood mitigating strategies of a levee/dike, surge barrier, coastal retreat, and elevation and show how each could modify the EWL damage function and lead to decreases in damages for specific EWLs. In contrast to more sophisticated cost-benefit analyses, our reduced-form framework aims to give a fast and clear illustration of the benefits of various forms of flood protection for EWL events of different frequencies (e.g., from common tidal events vs. rare coastal storm events) and under user-specified SLR scenarios. Once preferred mitigation strategies are chosen, more complex models could be used for further planning.

+ After Relocation: Reimagination of the Post-Retreat Landscape

Bella Purdy, MIT

After buyout programs are complete, how can vacated parcels be repurposed to protect remaining residents living in the floodplain? This proposal explores design and implementation strategies for transitioning acquired parcels into functioning, resilient landscapes. The intention of the proposal is to provide practitioners as a proxy for municipalities, community organizations, and residents with a digital toolkit which will help them better understand the complexities of the left behind block typologies. The digital toolkit will use three sites in the Metro New York City area to illustrate the ways in which post-disaster properties can be used not only to restore the floodplain and provide resilient, ecosystem services, but also provide vibrant, temporary-use spaces that will help communities maintain their quality of life. Ultimately, the post-retreat landscape digital design toolkit aims to deliver design mechanisms that work against climate-forced displacement. The thesis speculates that the redesign of post-retreat landscapes can help property owners maintain their quality of life at least throughout their lifetime, working against near-term displacement.

+ Coastal Zones Resilience to Climate Change in Oman: Adaptive Governance and Institutional Strategies

Elnazir Ramadan, Sultan Qaboos University

Coastal zones around the world have always attracted large population in view of their resources as they offer access points for maritime trade, recreational or cultural activities. Oman is a country with vast coastal zone in the south of Arabian Peninsula. Oman coastal zones represent an important access point in history of the country. In the present time these zones are undergoing tremendous changes in socio-economic and environmental values over the past few decades since the development and utilization of coastal zones has greatly increased due to high population growth. On the other hand, this population has likely high exposure to coastal hazards including sea-level rise and associated storm surge flooding effects. The aim of this study is to explore the inputs of government institutions and the community in the formulation of policy framework towards addressing urban climate change adaptation and resilience. The Study examines the role played by Government institutions and the community in climate change adaptation. The main question of the study addressed is focusing on adaptation response capacity, governance, institutional arrangements and communal and responses .The study methodology is based on qualitative and participative methods that were used to enable stakeholders both (local community members and government officials) as well as researchers to gauge information, identify demands and discuss proposals and solutions. Managing the coastal zone is a complex issue due to its importance in terms of human population size, coastal development and associated climate change hazards .Coastal flooding risk associated to tropical cyclones (TCs) is nowadays a major concern in low-lying and populated areas in Oman. In the past few years there have been devastating examples in the Arabian Sea (i.e. Gonu or Phet) that encourages better understanding, characterizing and prediction. The coastal zone also supports the widest array of ecosystems, with diverse habitats and associated ecology. The study results revealed that Government of Oman has worked out comprehensive coastal zone management plans towards protection of coral reefs, wetlands, mangrove, turtles and other resources, including land and groundwater resources in order to meet the challenges of environmental protection along with the development. Integrated coastal zone management (ICZM) is an approach of adopted by the government that seeks developing legislations for coastal zone protection, management plans, recovery and governance along with awareness raising. The (ICZM) approach implemented included a sort of controversial managed retreat programs.

+ Collaboration and Mitigation: The Case of Pelluhue Tsunami Reconstruction

Maria Garces Marques, Columbia University

Chile’s coastline is about 4,000 miles long, and over 3 million people (18% of its population), live in urban coastal zones, being one of the most exposed coastal areas in the world. On February 27, 2010, an 8.8 magnitude earthquake and tsunami hit Chile’s central zone, causing over US$300 million in damages and the loss of over 500 lives. Pelluhue, a coastal city in the Maule Region, was one of the most damaged: about 70% of its infrastructure was washed away hindering the livelihood of its residents, mostly dedicated to tourism and fishing. The Poster for this conference communicates research conducted during 2017 for a Master’s thesis on specific strategies employed during reconstruction processes that were able to restore Pelluhue and its community to a more resilient place, such as master plans, mitigation infrastructure, and housing typologies. Methods employed include field observations, literature review, and key informants, which encompassed all sectors involved in the reconstruction process.

Strong collaboration between multi-sector stakeholders, including the community, was key in order to guarantee a strong reconstruction process, in which every actor was held accountable. The result is a safe and resilient place for people to live in, considering potential climate threats. Disasters are an opportunity to improve from past conditions, integrating risk management and resilience building into the mix. The strategies employed in Pelluhue, such as coastal protection, mitigation park, and tsunami resistant housing, are some of many others that can replicate and scale up in other parts of the world without resulting in retreat. Pelluhue is a case study that was able, through an efficiently managed reconstruction, to reduce physical vulnerabilities through effective planning policies together with rebuilding a more resilient community. It took advantage of a critical situation and the economic resources that otherwise might not be available through traditional channels.

+ Estimating the Costs of 1m and 3m Sea-Level Rise in Chennai

Arjun Bhargava, Resilient Chennai, Greater Chennai Corporation (Arjun K Bhargava, A Ramachandran, Akshaya Ayyangar, Bhavani K Masillamani, Avilash Roul, Uthra Radhakrishnan, Prof. Sudhir Chella Rajan)

There is a limited understanding of the impact of sea level rise (SLR) on major coastal cities in India. It is estimated that nearly 40 million people in India will be at risk from SLR . As the fourth most populous metropolitan area in India with a population of over 8.5 million , and as one of India’s largest coastal cities, Chennai is vulnerable to SLR. We studied how 1m (scenario A) and 3m (scenario B) mean SLR might impact the coast of Chennai . We adopted a simple GIS framework using ArcGIS software to map inundation in Chennai and identified affected infrastructure. The study estimates the total economic loss of infrastructure from Scenario A as approximately Rs.7,91,790 crores ($116.49 billion) and approximately Rs. 10,68,009 crores ($157.13 billion) for Scenario B. Total economic loss is defined as the replacement cost of fixed assets and value of production of goods and services lost for one year, represented in terms of stock and flow variables for selected infrastructure, namely land, roads, bridges, ports, Special Economic Zones, power plants, substations, desalination and sewage treatment plants. It is important to note that majority of the loss (74 percent) occurs likely in Scenario A itself. For either scenario, the total loss from ports is estimated to be Rs. 5,55,035 crores ($81.66 billion), suggesting that the largest impact of SLR will likely be on ports. The two desalination plants will also likely be affected under scenario A suggesting the need to revive traditional waterbodies. The simple assessment might help cities develop an understanding of the potential impacts of SLR.

+ Impact Assessment of an On-Shoreline Highway Extension in Dakar (Senegal): Coastal Erosion and Flood Risks

Awa Bousso Drame, Sorbonne University and Columbia University (Professor Denis Mercier (Sorbonne University))

During the last two decades, the African continent is experiencing the highest urban growth rates estimated at 3.5% per year with certain African cities expected to represent 85% of the population by 2025. Among fast-growing capitals, Dakar concentrates 3.630.324 inhabitants in 2018, representing 48% of the urban population. The urban growth and sprawl of the Senegalese capital is led by driving forces as rural exodus from the inland and West Africa, in addition to its demographic growth of 2,7% (national scale). As a peninsula of 550 km², Dakar is reaching its limits, leaving peripheral coastal the only potential areas for new infrastructures developments, such as the extension of the existing northern highway so called “Voie de Dégagement Nord”. The 18km highway was launched by Senegalese government costing a total of 100 billion Fcfa (105 million US dollars), this aimed to reduce traffic jams and ease mobility. Reshaping both coastal and urban landscapes, the highway development is located in the Niayes region, a geomorphologic unit formed of coastal sandy dunes covered by filaos (Casuarina equisetifolia), starting from Dakar to Saint-Louis and supplying the country with market gardening. Through an geographical approach combining GIS, remote sensing, precipitation analysis’ and modelling of run-off flows, this study proposes an erosion and flood risk assessment to examine the situation before and after the highway extension. Between 2012 and 2018, the coastal sandy dunes covered by filaos (Casuarina equisetifolia) protected the inland from the sea, these were then converted into an extension of the highway VDN (Voie Dégagement Nord) and residential housing, in addition to the infrastructure development blocking the run-off flows to the sea. Furthermore, this study outlines the increasing pollution risk stemming from the Tivaouane-Peulh wastewater management unit developed between the VDN extension and the sea. Nevertheless, the flood management program (Projet de Gestion des Eaux Pluviales, PROGEP) is deemed inefficient while the environmental policy doesn’t reflect an integrated water management in Dakar urban planning. Dakar’s Northern coastline is already facing heavy swell reaching 2.5m (in December 2018) and frequent annual floods during the rainy season. Therefore, retreat can be a sustainable coastal management strategy reducing losses resulting from floods and balance priorities between coastal ecosystems protection and urban sprawl.

+ Transaction to Adaptation: Promoting Climate-Smart Land Use with Transfer of Development Rights

Ellen Plane, University of California, Berkeley

Sea level rise and an ongoing housing crisis are two major planning challenges facing municipalities in the San Francisco Bay Area. These challenges intersect: coastal flooding will reduce housing supply over the next century, exacerbating an existing shortage. In this policy proposal, I explore how transfer of development rights (TDR), a land use planning tool frequently used to reduce sprawl, could be used to promote both sea level rise adaptation and infill housing production. Under such a program, developers would buy credits to build additional density in designated infill areas, and the proceeds would be used to fund sea level rise adaptation. Adaptation strategies could include managed retreat approaches like buyouts and restoration, or the program could help fund resilient redevelopment projects in suitable areas. The use of TDR as a financing mechanism would not only raise funds for sea level rise adaptation but could also contribute to alleviating the acute housing shortage in Bay Area by promoting construction of new housing units. By planning receiving areas along transit corridors and near job centers, the TDR program can also help the region meet carbon emission reduction goals by reducing vehicle miles traveled. I conducted interviews, case studies, and geospatial analysis to make design recommendations for a regional sea level rise TDR program that promotes smart growth, ecological restoration, and social equity.

+ Remote Sensing Mapping of Changing Coastal Ecosystems in the Face of Increasing Anthropogenic and Natural Disturbance

Maria Tzortziou, CUNY, LDEO Columbia University (Brian Lamb, Kyle McDonald)

Connecting the terrestrial and aquatic landscapes, coastal habitat across the globe are increasingly being exposed to a wide range of environmental pressures. Rising sea level, increasing temperature, hurricanes, storm surge and eutrophication in the ocean, combined with urban development, agricultural intensification, shifts in precipitation patterns and changing hydrologic regimes on land, exert increasingly strong pressure on coastal ecosystems, affecting land-air-water biogeochemical exchanges and feedbacks, subsequently altering terrestrial and aquatic ecology, biological productivity, and biodiversity. Invariably intertwined with coastal ecosystems, humans strongly influence the ecological status of coastal habitat and their ability to respond to disturbance, while degraded coastal systems impact coastal communities and economies, and place people and property at greater risk of damage from coastal hazards. Space-based remote sensing provides a powerful tool for assessing coastal ecosystem exposure, vulnerability, and resilience to disturbance. Here, using a combination of radar and optical/IR satellite datasets, we apply multi-disciplinary remote sensing observations of both the terrestrial and aquatic landscape to improve space-based mapping of heavily urbanized coastal ecosystems, assess the status and change in their ecological characteristics, examine linkages to coastal population change and associated urban development, and identify locations that are most likely to be subject to future impacts.

+ Social Capital and Social Cohesion in Community Relocation

+ Urban Groundwater Flooding Driven by Sea-Level Rise

Xin Su, Stevens Institute of Technology (Valentina Prigiobbe)

The urbanization of coastal areas have been increasing along the East coast of the United States. Meanwhile, during the last century, the sea level has increased of approximately 0.35 m. Therefore, it is expected that several areas will be affected by marine flooding as well as groundwater flooding (or inundation), which is usually not accounted for in flooding forecast. Earlier studies show that the total flooded coastal area may exceed twice of marine flooding if groundwater flooding is considered . In addition, the aging of sewer system along coastal areas may favor flooding of the pipes and, therefore, more frequent discharge of in excess sewage towards waterways.

Here, a work is presented to investigate the influence of sea level rise on the water table of an urban shallow aquifer during dry weather condition (DWC). The aquifer is located underneath an urban area along the Hudson River Estuary (Hoboken, NJ). The watershed was implemented and comprises the shallow geology and the city plan, accounting for perviousness. Boundary conditions were provided by real time measurements at monitoring wells within the city and river level. Previous work from our group shows the evolution of the groundwater table in response to the tidal variation of the river to identify if inundation of aging infrastructure were possible. Results show that currently more than 60 % of the sewer may experience groundwater infiltration for a total of 50 % of excess water within the system, which contributes in activating discharge of sewage. Simulating the repair 1 of the damaged pipes, discharges diminish occurring only upon significant precipitation, but the water tables rises. Eventually, during high tide, the groundwater can flood the low-lying part of the city.

Overall, this work highlights the susceptibility of shallow aquifers in coastal urban areas and suggests that the importance to account for groundwater inundation to improve flooding predictions.

+ Vulnerability of Coastal Land Use to Sea-Level Rise, a Case Study: Jask County in Iran along the Sea of Oman

Lida Davar, University of Tehran, University of California, Santa Cruz (Professor Gary Griggs (University of California, Santa Cruz), Professor Afshin Danehkar (University of Tehran), Professor Abdolrassoul Salmanmahini (Gorgan University), Dr.Babak Naimi (University of Amsterdam), Professor Hossein Azarnivand (University of Tehran)}

Global mean sea-level rise (SLR) will continue during the 21st century, very likely at an increased rate. The rise will likely be in the range of 0.26 to 0.55 m for RCP2.6, and 0.45 to 0.82 m for RCP8.5 by 2100 (IPCC). Current and future land uses will be affected by the projected sea-level rise. Because of the vulnerability of different coastal land (both developed and under development) to inundation, it is timely to implement appropriate responses within the existing coastal zone management plan. In this vulnerability assessment, we identified the potential land use vulnerabilities of Jask County’s coastal zone in the southern part of Iran under a high estimate of sea-level rise for the RCP8.5 scenario. An inundation map (created applying NOAA’s modified bathtub model) and current land use map (categorized in 7 classes) were the two main data sources used to assess vulnerabilities. The results indicate 448 sq. km of the coastal zone will be inundated, which encompasses wetland/inland water bodies (36%), bare (potentially developable) lands (35%), poor-rangeland (14%), undefined/military zones (12%), forest/woodland (3%), aquaculture (1%) and urban areas (1%). Although only 1% of the entire coastal area falls into the urban category, this includes the most populous city in county, a strategic port, as well as airport and industrial zones. For these reasons, developing an effective adaptation plan and putting it into practice within the regional integrated coastal zone management plan would facilitate sea-level rise impact reduction as well as sustainable future development.