Reducing Coastal Risk on the East and Gulf Coasts (2014) / Chapter Skim
Currently Skimming:
1 Introduction
1 Introduction
Pages 11-38
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 11... ...
East and Gulf Coasts, and discusses how those risks have changed and are continuing to change. General strategies that can reduce risk and help make communities more resilient to coastal storms are also discussed.
|
From page 12... ...
. Appendix A provides a table of major coastal storms that have struck the United States since 1900 -- most of which made landfall on either the East or Gulf Coasts.
|
From page 13... ...
SOURCE: Data from http://www.ncdc.noaa.gov/billions/events. FIGURE 1-1 Average number and costs associated with billion-dollar coastal storm events in the United States between 1980 and 2013 by 5-year time increments.
|
From page 14... ...
and they typically have low topographic slope, meaning they lack the most effective natural defense against coastal storm surge and wave damage -- vertical elevation of the land near the water's edge. Natural cycles in tropical cyclone activity and observational bias in data sets before the modern satellite era (mid-1960s)
|
From page 15... ...
INTRODUCTION 15 FIGURE 1-2 Estimated average return periods (years) for all hurricanes (top)
|
From page 16... ...
(2013) calculated that the return periods for Hurricane-Sandy– level storm surges would be reduced by a factor of approximately 4, with higher sea-level rises further reducing the intervals between major inundation events.
|
From page 17... ...
Gulf of Mexico and Atlantic Coasts as being subject to increased risk of storm surge damage and flooding due to sea-level rise combined with coastal storms. Impacts will occur to homes, critical infrastructure, cultural and historic resources, agriculture, ports, tourism, coastal resources, and coastal ecosystems.
|
From page 18... ...
The federal government's assistance to disaster victims is well illustrated by the large increase in the past 60 years in the number of Presidential disaster declarations that have occurred (from ap
|
From page 19... ...
in coastal storm-related Presidential disaster declarations4 (Figure 1-5)
|
From page 20... ...
Understanding, managing, and reducing risk are foundations for build ing resilience. Risk is "the potential for hazards to cause adverse effects on TABLE 1-3 Change in Percentage of Federal Aid Following Major Tropical Cyclones, from 1955-2012 Disaster Federal Aid as a Percentage of Total Damage Hurricane Sandy (2012)
|
From page 21... ...
. Thus, flooding or overland waves caused by hurricanes or other strong coastal storms are the primary hazard -- not the storm or the coastal storm surge itself.
|
From page 22... ...
than on other infrastruc TABLE 1-4 Risk Reduction Measures Linked to Components of Risk Reduction Risk Reduction Probability of Hazard (Flooding, Consequence Wave Coastal Risk Mitigation Measures Damage) Exposure Vulnerability Surge barriers X Levees, sea walls X Beach nourishment and dune building X Relocation X Land-use restrictions X Elevating and flood-proofing structures X Flood warning and preparedness programs X X Flood insurancea X aIf flood insurance is appropriately priced, the result should communicate risk and may spur additional mitigation measures, thus reducing vulnerability in addition to transferring risk to a broader risk pool.
|
From page 23... ...
Communities can work collectively to determine an acceptable level of residual risk based on their risk tolerance and the benefits and costs of additional risk reduction measures (see Chapter 4)
|
From page 24... ...
approach recommends investment in coastal risk reduction measures to drive residual risk below a specified level (such as a 1 percent annual chance of exceedance, also known as a 100-year event; Box 1-3)
|
From page 25... ...
Many U.S. studies have concluded that the 1 percent chance event is inadequate as a flood risk reduction design basis for urban areas (e.g., Galloway et al., 2006; ASFPM, 2007; NRC 2009)
|
From page 26... ...
The development of the area east of the Industrial Canal, which contains 50 percent of New Orleans' land area, is especially suggestive of the interaction between flood risk reduction measures and development. In 1960, before the new levee plan, eastern New Orleans consisted of a few scattered residential and commercial structures.
|
From page 27... ...
very different time and spatial scales, storm surge and waves respond quite differently to hazard mitigation strategies and therefore these responses are discussed individually. Measures to Reduce the Hazard -- Hard Structures Hard structural measures to address coastal storm hazards are typically static, engineered features designed to reduce wave damage and flooding, and they may also decrease shoreline erosion.
|
From page 28... ...
R02656 Fig 1-6.eps infrastructure" or "hard engineering," these structures include seawalls, levees and floodwalls, and surge barriers: · Seawalls are constructed parallel to the shoreline to reduce impacts from storm surge and waves to developed lands behind the seawall. Seawalls may be vertical or curved walls (Figure 1-6)
|
From page 29... ...
. Nature-based coastal risk reduction strategies are designed and engineered to mimic natural features for the purpose of attenuating storm surge.
|
From page 30... ...
30 REDUCING COASTAL RISK ON THE EAST AND GULF COASTS FIGURE 1-7 Schematic of a floodwall paired with a levee for flood risk reduction along a canal (top) and a levee with floodwall along the London Avenue Canal in New Orleans, Louisiana (bottom)
|
From page 31... ...
However, replenishment brings additional ecological impacts, as discussed in Chapter 3, and replenished beaches may have a different slope than natural beaches, which can alter the incident wave conditions. Other potential nature-based coastal risk reduction strategies include conservation and/or construction of wetlands and oyster reefs, which may also provide additional ecosystem services benefits.
|
From page 32... ...
Recent cost data are not available, but the percentage of overall coastal risk reduction costs represented by hard structural measures has likely increased in the past decade with the post-Katrina construction of the Hurricane Storm Damage Risk Reduction System. Data used to compile the bottom figure are listed in Appendix B
|
From page 33... ...
Flood preparedness programs might include delineation of flood hazard areas, effective communication of risks to community residents and developers, development and communication of evacuation plans, and flood insurance for those at risk of flooding. If appropriately priced, flood insurance serves as both a risk transfer mechanism and an effective risk communication tool.
|
From page 34... ...
. The committee was subsequently reconstituted for specific focus on reducing flood risks from coastal storm surges along the East and Gulf Coasts and was tasked to address the following questions: 1.
|
From page 35... ...
INTRODUCTION 35 FIGURE 1-11 Example of one approach for elevating a house above the base flood elevation (BFE)
|
From page 36... ...
Following this introduction, the statement of task is addressed in three subsequent chapters of this report: · Chapter 2 presents the institutional landscape for coastal risk man agement in the United States, highlighting major programs and re cent budgets, and discusses the mechanisms by which the USACE develops and implements coastal risk reduction projects. · Chapter 3 summarizes the current state of knowledge on the ef fectiveness of coastal risk reduction measures based on proven per formance under coastal storms.
|
From page 37... ...
. · Chapter 4 outlines key principles to guide future investments in coastal risk reduction, including a discussion of a benefit-cost ap proach constrained by acceptable risk for prioritizing coastal risk measures at a regional or a national scale (Tasks 3 and 4)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.