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Risk Level - High

According to the National Hurricane Center (NHC), a branch of the NOAA, there are several different classifications of tropical systems that are categorized based on the system’s maximum sustained surface wind speeds. Hanahan residents are generally aware that the classifications are as follows:

Locations and Paths of Natural Hazards

• Tropical Depressions – 39 mph winds or less;

• Tropical Storms – 39 to 73 mph winds;

• Category 1 Hurricane – 74 to 95 mph winds;

• Category 2 Hurricane – 96 to 110 mph winds;

• Category 3 Hurricane – 111 to 130 mph winds;

• Category 4 Hurricane – 131 to 155 mph winds; and

• Category 5 Hurricane – Over 155 mph winds.

South Carolina has an 80% chance annually of being impacted in some way by a depression, storm, or hurricane.8 Hurricane season for the South Atlantic and the Gulf States begins in June and lasts until the end of November. Trends reveal that August through October are the most common months, however, there have been systems that occur as early as February in the past. As seen on Map 15, there have been several tropical storms and hurricanes that have impacted the area in and around Hanahan. Since 2000, there have been five hurricanes, all of which were category 1, that have been within 50 miles of Hanahan: Charley and Gaston (2004), Matthew (2016), Isaias (2020), and Ian (2022). 9

Tropical systems can create conditions for several additional hazards besides the intense wind including heavy rainfall causing flooding, storm surges, and tornadoes. These additional hazards make tropical storms and hurricanes one of the most costly and dangerous natural hazards that can occur in Hanahan.

According to the South Carolina Emergency Management Division (SCEMD) Hurricane Evacuation Zones Map (last updated in 2021), Hanahan, along with most of Berkeley County, is within Zone G –Berkeley County of the Central Coast Region. The primary evacuation routes for Hanahan would be I-26, US 52, US 78, and US 176.

FIGURE 37: SOUTH CAROLINA EMERGENCY MANAGEMENT DIVISION HURRICANE EVACUATION ZONE MAP

Storm Surges

The NHC defines a storm surge as an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. In the past, storm surges have been a leading cause of death during tropical systems and can cause massive amounts of damage to property. Coastlines with a shallow or gentle slope, such as South Carolina’s, typically generate larger, more intense storm surges due to the progressive buildup of water and pressure before making landfall.

Storm surges are not strictly a coastal community hazard, but can impact communities several miles inland, especially with large rivers like the Ashley, Cooper and Wando flowing miles inland. The height and intensity of storm surges are not dependent on the category of the tropical system, therefore, adhering to storm surge warnings and alerts during all tropical systems is important for maintaining general health and safety.

8 Source: South Carolina Department of Natural Resources: Hurricanes Comprehensive Summary Report

9 Source: NOAA Historical Hurricane Tracker

Potential Impacts

Hurricanes can cause a wide range of impacts to a community before, during, and after a storm event. Although Hanahan is located several miles inland, the city can expect to experience some of the more common impacts of a tropical system such as fallen trees, downed powerlines, power outages, property damage, and temporary closures of schools, services, and businesses. City emergency service personnel should continuously coordinate with adjacent jurisdictions, state, and federal agencies to prevent as much damage as possible. Using social media and the city website as a mean to distribute storm updates and evacuation information is crucial in keeping residents informed and aware of the developing situation. Other mitigation efforts could include identifying potential shelter locations, requiring storm resilient infrastructure and materials for new and redevelopment projects, and prepare disaster kits for distribution.

Flooding

Risk Level - Immediate

The Federal Emergency Management Agency (FEMA) defines a flood as a general or temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties. Changing climate and weather patterns, environmental conditions and impervious surface coverage may affect the frequency and intensity of a flood. Flooding was a key issue identified in the public participation survey and therefore warrants an important discussion on the different types of flooding, the causes/effects, and some best management practices to help mitigate the issue.

Flooding can result from multiple sources – rain from thunderstorms and tropical systems can cause inland and riverine flooding, while coastal flooding can result from a combination of storm surge, wind, and rain. These different types of floods (rain, riverine, and coastal), however, can be attributed to the same weather event and can co-occur. Hanahan is especially susceptible to rain and riverine flooding due to its proximity to the Cooper River, Goose Creek, and the Goose Creek Reservoir. As seen in Map 16, the 100- and 500-year floodplain generally follows Goose Creek, Turkey Creek, and some unnamed tributaries into the Hanahan neighborhoods. Areas that are within the 100-year floodplain or high-risk flood zones are designated by FEMA to be in the Special Flood Hazard Area (SFHA). Properties within this area are federally required to have flood insurance, while properties within the moderate to low-risk flood zones (500-year floodplain) are not federally required, but are recommended, to have such insurance.

MAP 16: 100-YEAR AND 500-YEAR FLOODPLAINS