Section Introduction

Transcription

1 Section Introduction 1.1 What Is Hazard Mitigation? Hazard mitigation is an action taken to permanently reduce or eliminate long-term risk to people and their property from the effects of natural hazards. Strategy for Hazard mitigation planning is the process that analyzes a community s risk from natural hazards, coordinates available resources, and implements actions to eliminate risks Tennessee Emergency Management Agency 1.2 Narragansett: Geography and Hazards Narragansett is essentially a peninsula, with Narragansett Bay to the east, Sound to the southeast, and Point Judith Pond and Narrow River to the west. The coastal environment defines the character of the town, and is a major attraction for tourists and residents alike; however, it also makes Narragansett vulnerable to natural hazards. The town s 49 miles of coastline vary from steep, rocky shores to low, sandy beaches. The town is a growing suburban community coastal areas, which a decade ago were home to summer cottages, now support dense residential and commercial uses. The Hurricane of 1938 (Category 3) 1 was the last 100-year flood (1 percent chance of occurrence in any given year) to hit Narragansett. Therefore, much of the at-risk population has never experienced a major storm event. Narragansett experiences a few nor easters each winter. The town has never had any serious problems in dealing with wildfires, snow, ice or earthquakes. 1.3 Goals and Objectives Narragansett adopts this mitigation strategy for the purpose of enhancing quality of life, protecting property, and preserving resources for residents and visitors. This will be accomplished by: Implementing hazard mitigation actions in order to protect Narragansett s cultural, historical, structural and natural environment. Promoting educational opportunities to introduce residents and visitors to the risks of natural hazards and the various appropriate mitigation strategies that can be taken. This municipal strategy, as approved by the State Hazard Mitigation Committee (RI SHMC), 2 is consistent with state objectives for natural hazard mitigation. The role of the RI SHMC is to review, grade and prioritize all hazard mitigation activities and grants that come through the Rhode Island Emergency Management Agency (RIEMA). This committee is also responsible for reviewing and approving revisions and updates to the state hazard mitigation plan ( 409 Plan). The information that is compiled in this municipal strategy will be incorporated into the state hazard mitigation plan. 1 From the Saffir Simpson Hurricane Disaster - Potential Scale (ranging from 1 to 5 with Category 5 having the highest potential winds). 2 The members of the RI SHMC are listed under the acknowledgement section of this document. 7

2 Strategy for 1.4 Mitigation Benefits Mitigation actions help safeguard personal and public safety. For instance, retrofitting bridges can help keep them from being washed out, which means they will be available to fire trucks and ambulances in the event of a storm. Another important benefit of hazard mitigation is that money spent today on preventative measures can significantly reduce the impact of disasters in the future, including the cost of post-disaster cleanup. This municipal hazard mitigation strategy will minimize the economic and social disruption that can result from multiple natural hazards. Formal adoption and implementation of this strategy will help Narragansett gain credit points under the Federal Emergency Management Agency s (FEMA) Community Rating System (CRS). CRS provides discounts on National Flood Insurance Program (NFIP) premiums for property owners in communities that participate in this voluntary program. Points are given to municipalities that form a Local Hazard Mitigation Committee (LHMC). Communities also receive points if they involve the public in the planning process, coordinate with other agencies, assess the hazard and their vulnerability, set goals, draft an action plan (municipal hazard mitigation strategy), and adopt, implement and revise the plan. Non-federally owned open space land in floodplains can also help a municipality gain credit points under the CRS program. In addition, open land enhances the natural and beneficial functions that floodplains serve and helps prevent flood damage. The adoption of this mitigation strategy will increase Narragansett s eligibility for federal grants, which include FEMA s pre-disaster Flood Mitigation Assistance Program and its post-disaster Hazard Mitigation Grant Program (see Appendix D). RIEMA gives funding priority to municipalities that have completed a risk assessment and have created well-thought-out mitigation projects that include detailed information on cost, responsible party and time frame for completion of projects. Predisaster planning will also help post-disaster operations become more efficient. For instance, procedures and necessary permits will be in place, as will clear priorities for mitigation during reconstruction. The state emergency response effort will run more smoothly because of the guidance provided in this strategy. Narragansett had to dig out from under the sand and debris deposited by Hurricane Bob in Photo courtesy: Coastal Resources Center 8

3 Section Hazard Risk Assessment 2.1 Hazards, Risk and Vulnerability Strategy for Definitions Hazard refers to an extreme natural event that poses a risk to populated areas. Hazard risk assessment determines which areas of the town may be affected by natural hazards, how likely it is that a given hazard may occur and how intense the hazard might be. Risk Risk can be defined as hazard; danger; peril; exposure to loss, injury, or destruction * or the possibility of suffering harm or loss. * Natural hazard risk assessment describes the magnitude, duration and probability of the hazard event. For example, risk assessment estimates potential wind speeds and storm surge for a specific area. Vulnerability Vulnerability can be defined as susceptibility to injury or attack. * Vulnerability indicates what is likely to be damaged by the identified hazards and how severe the damage might be. For example, if an area is determined to be at risk of flooding, vulnerability estimates could include residential property losses, impacts to the tax base and damages to public infrastructure. The vulnerability assessment is often communicated in terms of the number of lives and the value of property in the high risk areas. To initiate the risk and vulnerability assessment process, Narragansett s LHMC (which consists of the town planner, engineer, fire chief, public works director, building inspector and town manager), examined the town s risk from natural hazards and identified its vulnerabilities to those risks. The LHMC used the Risk Assessment Matrix (see Table 4) and GIS maps (see Map 1 and Map 2) as tools to help with this process. The risk and vulnerability assessment formed a solid basis on which the LHMC established mitigation priorities. Sources of information used during the assessment include U.S. Army Corps of Engineers studies, RIEMA reports, municipal records, local knowledge and historical accounts. *All definitions found at Dictionary.com ( June 14,

4 Strategy for Table 1. Historical Damages The following table gives a brief account of some of the damages that Narragansett has experienced from past storms. Name/Date of Storm Examples of Damaged Areas Total Cost of Damage to the Town Great Gale of September foot waves were reported. Not known Lighthouse keeper died. New breachway formed on Point Judith Pond. 3 Hurricane of 1938 This storm washed away cars, destroyed $2 million in damages occurred mostly (the last 100-year flood to hit the state) bridges and buildings, and killed 18 people along the coastline (in 1935 dollars) in Narragansett. The Dunes Club was reduced to shambles. Bonnet Shores, while not nearly as developed as today, sustained extensive damage. Middlebridge Bridge was completely washed out, and the seawall along Ocean Road was destroyed. The town s shorefront barriers were wiped out by both the 1938 and 1954 hurricanes and in many instances have been heavily redeveloped in spite of similar risks today Storm Tides were reported as high as Boon Street. Not known Hurricane Carol in 1954 Floodwaters rose more than six feet above $14.65 million* in property damage to Beach Street (in the town s business center). Point Judith and Potter Ponds Businesses and homes in Scarborough were destroyed. The State Pier and Galilee Road were submerged under more than two feet of water. The Bonnet Shores Beach Club was destroyed. Houses were swept off their foundations at Matunuck, Jerusalem and Sand Hill Cove. As a result of storm-surge, waters \ rose 15 to 20 feet above mean sea level in upper Point Judith Pond, causing damage to buildings, power lines, water mains and eroded bluffs. 4 The bridges to Great Island and to Jerusalem across Potter Pond inlet were destroyed. Dunes were eroded and debris was dumped onto beaches. Hurricane Gloria 1985 Damage to buildings on town beach $546,448* was given to the town from ($42,000) and to roof of the Towers, RIEMA for disaster assistance a historic landmark ($5,000) Hurricane Bob 1991 The major damage was caused by wind; $555,410* in clean-up fees for public flooding was minimal. Debris blocked property alone roads and caused extensive structural damage. The town lost power for 3 to 4 days. The Coast Guard House restaurant, a historic structure, was severely damaged. Snow Storms 1996 (several during this year) Mostly tree damage. $18,541* * For comparison purposes, dollar amounts have been converted to dollars. Wind (hurricanes, nor easters and tornadoes) 3 Virginia Lee, RI CRMC, Salt Pond Region SAMP,

5 Historically, Narragansett has sustained damage from flooding and high winds associated with hurricanes, nor easters and heavy rains. However, this strategy addresses multiple natural hazards, even those assessed with low probability. Wind (hurricanes, noreasters and tornados) Since 1635, Narragansett has experienced 71 hurricanes of varying magnitude. The strong winds that accompany hurricanes can create debris problems including downing power lines, which can lead to business interruption. Wind pressure and airborne debris can cause building components (i.e., gutters, screened enclosures that aren t structurally tied to the house, roof coverings, shingles, car ports, porch coverings, overhangs, siding, decking, windows, walls and gables, etc.) to fail. Winddriven rain can enter openings in either the roof or wall envelopes. The wind hazard maps developed for today s model building code can estimate what community-wide wind speed the town can expect. A look at historical wind damage can also reveal special wind hazard risks. For instance debris, especially fallen tree limbs, was a major problem with Hurricane Bob. Strategy for Flood (riverine flooding, coastal storm surge, erosion and sea level rise) Floodplains in Narragansett include A, V and X zones. A zones are areas that would be inundated by the 100-year flood. V zones are velocity zones that are subject to breaking wave action where waves greater than 2.9 feet are forecasted during a 100-year flood or storm surge. 5 X zones are areas that would be inundated by the 500-year flood. About 40 percent of the town is located in flood zones (counting the 500-year flood areas). Map 1, Risks depicts the FEMA flood zones as well as the U.S. Army Corps of Engineer s hurricane evacuation areas. Hurricane inundation areas are determined by using the National Hurricane Center s SLOSH (Sea, Lake and Overland Surges from Hurricanes) model. These areas will suffer most as indicated by projected hurricane direction, forward speed, landfall points and high astronomical tides. The recorded storm surge in downtown Narragansett during the Hurricane of 1938 (a category 3 storm) was 13.7 feet above mean sea level. This hurricane hit during the autumnal equinox, during which the highest high tide of the year occurs. Hurricane Carol in 1954 (also a category 3 storm, but not as intense as the 1938 hurricane) brought an even higher storm surge of 14.4 feet above mean sea level. 6 Narragansett s exposed shoreline not only makes the town vulnerable to coastal flooding and erosion from hurricanes and nor easters, but also to relative sea level rise (approximately 25 centimeters per 100 years). 7 Sea level rise may displace beaches landward, drown coastal marshes and increase flooding problems. 8 In addition, sea level rise will probably increase the frequency of sand overwash. Any amount of future sea level rise will result in an increased rate of coastal erosion as waves will break higher on bluffs and dunes along the open shoreline for any given storm intensity. 9 According to Clark, the threat of accelerated global sea level rise, which is projected to be between 13 cm and 94 cm by 2100, portends increased flood and relative sea level rise due to subsidence which could amount to an additional 20 cm by Wind, snow, and ice damage may also increase, depending on the highly uncertain effects of global climate change on storm frequency and intensity. 10 Map 3 (Harwood 1993) shows the predicted impact of sea level rise on expanding flood zones 5 Victor Parmentier, RI State Floodplain Manager, pers. comm. 6 David Vallee, National Weather Service, pers. comm. 7 RI CRMC, Narrow River SAMP, RI CRMC, Narrow River SAMP, RI CRMC, Narrow River SAMP, Clark,

6 Strategy for in Because sea level rise estimates vary, planning for specific scenarios is difficult, but the response planned can be adjusted as estimates become more precise. 11 Wildfires The three principal factors affecting wildfires are topography, fuel and weather. For example, fire travels downslope much more slowly than it travels upslope, and ridgetops often mark the end of a wildfire s rapid spread. Also, a fire s rate of spread varies directly with wind velocity. Other hazards may trigger wildfires, and wildfires may contribute to other hazards. For example, high winds can result in downed power lines, which can start fires. Wildfire is not considered a high risk in Narragansett because most residential and developed areas of town have fire hydrants every 500 feet. Once a year, the fire department re-evaluates the need for hydrants and the water division installs more if necessary. In general, there is plenty of water storage and few wooded sections or grassy fields. However, special attention should be given to areas of urban/wildland interface where vegetation and the built environment provide fuel. According to the fire chief, the only areas that might be a problem are the bird sanctuary in Kenyon Farm (west side of Point Judith Road) and the open fields along Boston Neck Road. Of special concern is Kenyon Farm, which has narrow roads that might inhibit fire truck access. Snow and Ice (severe winter storms) Winter storms often spawn other natural hazards, such as extreme winds, coastal erosion and flooding. The weight of accumulated snow or ice can damage infrastructure and possibly cause buildings to collapse. Utility and power lines can break from the weight of snow or ice, coupled with strong winds. This could put residents at risk of losing heat, electricity and water (if using well water). Flat-roofed buildings face a more serious structural risk from heavy snowfall. Snow melting poses problems as well, such as road flooding in low-lying areas. Because of its relatively mild coastal climate, the town has not had any serious problems with snow and ice. Earthquakes Earthquake risk in Narragansett is considered minimal. Narragansett has seen a total of 15 earthquakes since 1928, with one in June 1951 registering 4.6 on the Richter Scale. Most of the town is built on Narragansett Pier granite, which is a very solid substrate. Narragansett enforces the state building code, which has been in existence since 1977 and has standards for new construction and major reconstruction of buildings so that they are built to withstand an earthquake that registers 3.0 on the Richter Scale. In general, buildings that are most at risk from earthquakes are old masonry buildings and large structures, such as the town hall, buildings on the University of s Bay Campus, the high school and the elementary school. FEMA has recently developed a software package called HAZUS to help assess the risk from earthquakes. Information in this database includes building materials, design levels, economic value, population and bridges. The model determines what damages can be expected in an area in the event of a severe earthquake. The state is now working on compiling more state-specific datasets for use with this software program that would supplement the generic Northeast states information that is currently used. Without data specific for Narragansett on such things as transportation, utility systems, hazardous materials, demographics, vehicles, building stock and essential facilities, it is impossible to do an accurate risk assessment for Narragansett using this software. 11 RI CRMC, Narrow River Special Area Management Plan,