Importance of Neighborhood Aspect Ratio and Storm Climate to Adaptation Efforts to Reduce Coastal Flood Mortality

Low-lying Coastal Landfill Neighborhoods (CLaNs) often have a large aspect ratio, defined here as the coastline length divided by neighborhood width, due to the common practice of reclaiming fringing wetlands along tidal waterways. Flood risk reduction for CLaNs frequently involves elevated barriers, in the form of berms, seawalls, or levees, which reduce risk but cannot completely eliminate residual risk (e.g., due to overtopping during extreme events). Managed retreat is an alternative approach for flood risk reduction, the general idea of which is to strategically ban development in hazard zones, relocate structures, and/or abandon land. This study aims at exploring the tradeoffs between elevated barriers and managed retreat in terms of both CLaN aspect ratio and storm climate, for both short-term and long-term risk reduction with sea-level rise. Hydrodynamic flood modeling of an idealized CLaN protected by different adaptation plans is used to simulate flood conditions and mortality for a range of storm surge amplitudes for both the present-day and under different sea-level rise scenarios. Results show that for a berm and a case of managed retreat of an equal cost, retreat becomes more beneficial than the berm in terms of mortality risk reduction for neighborhoods with a larger aspect ratio. The study also shows that berms are generally less effective for reducing mortality in regions with less common but higher intensity storms. This study reveals the potential of idealized modeling to provide fundamental insights on the physical factors influencing the efficacy of different adaptation strategies for mortality risk reduction.

The Role of Urban Planning and Landscape Tools Concerning Flash Flood Risk Reduction Within Arid and Semiarid Regions

This chapter highlights some substantial questions inquired by researchers to comprehend the flood risks (FRs) that occur in their cities as follows: (1) What is the impact of flooding on urban areas? (2) what effect does urbanization have on FR? (3) What are the existing nonstructural and structural mitigation measures for urban flooding? and (4) What is the role of urban planning and landscape tools in flood risk reduction (FRR) for cities as well as their inhabitants? The main messages in this chapter could be summarized as follows: (1) Comprehension of both the sources and types of flooding is vital if proper FRR measures are to be determined, (2) Unplanned urban growth could seriously put lives and properties at high risk (3) Land use planning and regulation, and Sustainable infrastructure for stormwater management through landscape architecture are fundamental measures for future FRR (4) The application of the urban planning approach for FRR in arid and semiarid regions has not yet received adequate attention and facing many challenges for its implementation, and finally (5) the combination of structural and nonstructural mitigation measures in spatial planning could be much more effective than using one type of measure alone.