Corps of Engineers, partners lead Hurricane Evacuation Study for Maryland

Published Sept. 26, 2017

Maryland typically has to deal with the impacts of tropical storms or nor’easters rather than hurricanes. However, while North Carolina’s Outer Banks breaks up the majority of stronger hurricanes before they reach the coast of Maryland, the state is not immune, explained Thomas Laczo.

Laczo is a coastal engineer with the U.S. Army Corps of Engineers, Baltimore District.

Maryland was significantly impacted by Hurricane Isabel that made landfall in 2003. The state experienced substantial storm surge of 6 to 8 feet above normal tide levels in some areas and even breached the Corps’ ecosystem restoration project at Poplar Island in two spots due to elevated water levels and large waves.

So, how is Maryland getting prepared for the next major storm?

Laczo is currently managing a Hurricane Evacuation Study for the state though the National Hurricane Program (NHP).

NHP is administered by the Federal Emergency Management Agency (FEMA), in partnership with the National Oceanic and Atmospheric Administration’s (NOAA) National Hurricane Center (NHC) and the Baltimore District, as a part of the Corps’ Planning Center of Expertise for Coastal Storm Risk Reduction. NHP’s mission is to support citizens and first responders in building, sustaining and improving the nation’s capability to prepare for, protect against and respond to hurricanes.

“As part of the National Hurricane Program, the Army Corps helps develop and maintain products and tools to help with planning and decision making for emergency managers,” said Carla Quinn, Baltimore District NHP lead.

Maryland’s Hurricane Evacuation Study

The Maryland Hurricane Evacuation Study consists of four main parts: hazards analysis, evacuation zone development, vulnerability analysis and transportation analysis.

“The hazard analysis helps decision makers at the Maryland Emergency Management Agency understand the maximum flooding associated with storm categories for hurricanes,” said Debbie Hardick, Baltimore District environmental protection specialist. “We concentrate on storm surge because it is typically the most life-threatening hazard that coastal communities face during a hurricane.”

To calculate the maximum potential storm surge, NOAA’s NHC uses the SLOSH (Sea, Lake, and Overland Surges from Hurricanes) model. To create the products used for evacuation planning, SLOSH is run several thousand times with hypothetical hurricanes under different storm conditions.  

“The peak high-water value at each particular location is recorded to capture a worst-case snapshot for a particular storm category,” said Quinn. “This composite approach is regarded by NHC as the best for determining storm surge vulnerability for an area since it takes into account forecast uncertainty.”

In addition to providing the worst-case scenario, NHC provides model outputs for specific locations focused by storm category, forward speed and trajectory. 

Based on information pulled from NHC’s simulations, the Corps creates maps that show inundation areas (or areas flooded) associated with each storm category, along with the maximum potential depth of water in those areas.

“These maps provide great input for developing evacuation zones,” said Hardick. “For instance, we know that on the eastern shore of Maryland there is more surge risk potential in a hurricane heading northwest rather than northeast. Therefore, when forecast information is available to identify the category and direction of an incoming storm, this knowledge could potentially help reduce over-evacuations, which is particularly important during tourist season.”

Evacuation zones are usually developed by the local county government with technical support from the state, FEMA and the Corps. Storm surge inundation area maps form the basis of the zones, but they are adjusted to local conditions. The boundaries are often times based on major roads, water, zip codes and local landmarks, so they are easier to communicate to the public.

The vulnerability analysis follows evacuation zone development. This analysis identifies the population, critical facilities, shelters, roadways and mobile home communities within each inundation area and evacuation zone.

“This information can help show what kind of shelter demand you are looking at and also the number of potential evacuees with the main intent of saving lives,” said Hardick. “It is also valuable data for operational and recovery planning.”

The final step in the study process is the transportation analysis that uses data from the other analyses to determine evacuation clearance times, which is the time required for all vehicles to get out of the evacuation zone, until the last vehicle reaches an assumed point of safety.

“We gather input from local emergency management, key traffic law enforcement officials and the Department of Transportation to gain an understanding on how the roadway network can support evacuation decisions,” said Hardick.

This analysis includes not only evacuation routes and scenarios, roadway capacities and travel destinations, but it also includes demographics and behavioral assumptions.

Information gathered in this study feeds a Hurricane Decision Support Platform, which is a storm tracking and decision support tool that the Corps operates and maintains through the program.  

“It is a big aggregator of information from many different pieces,” said Laczo.

The platform combines live feeds of tropical cyclone forecast information with data from various state hurricane evacuation studies.

“It provides local emergency managers with the best information available to make evacuation decisions,” said Quinn. “The Corps also provides the emergency managers with training on how to use the tool.”

Emergency managers in every coastal state from Texas to Maine, and Hawaii, Puerto Rico and the U.S. Virgin Islands have access to this platform.

Why update the study now?

The last time this study was conducted was in 2009 and 2010 when the Delmarva Peninsula that encompasses the eastern shore had a study separate from Maryland’s western shore counties. The Delmarva study was executed as a three-state effort in order to address evacuation transportation issues since they all share the same road network. This current study encapsulates all of Maryland’s vulnerable counties. Norfolk and Philadelphia Corps districts are conducting their own hurricane evacuation studies for Virginia and Delaware, respectively, and overlapping information will be shared.

There are several reasons why it is necessary to promptly conduct this study.

There is new SLOSH data from NHC that incorporates key information from Hurricane Sandy; populations are increasing along the coast; roadway infrastructure is changing; and there is new LIDAR (Light Detection and Ranging) data to model land elevation and measure projected storm surge heights.

In 2016, if Hurricane Matthew had not lost speed and had continued to work its way up the east coast, multiple states would have needed to evacuate.

“One great thing about this study is that it lets you envision things you may not have otherwise been ready for, such as transportation bottlenecks created by mass evacuations, and the need for strong interstate communications,” said Laczo.

The study is expected to be completed by the start of the 2019 hurricane season.