Peter Datin, Derek Stedman and Vahid Valamanesh
Peter Datin is a Director - Model Development, RMS
Derek Stedman is a Lead Modeler - Model Development, RMS
Vahid Valamanesh is a Lead Modeler - Model Development, RMS
After a major hurricane or a similar natural disaster, RMS routinely sends modelers and engineers into the affected region to survey the destruction. This field reconnaissance in the immediate aftermath of an event serves several purposes:
Of course, RMS is always concerned about the safety of its personnel and waits until it is safe to send anyone to the disaster areas. We also have to make sure that we can travel to the different areas affected by the disaster without too much difficulty.
Figure 1: RMS Disaster Response Team in North Carolina after Hurricane Florence
Hurricane Florence Damage Observations
After Hurricane Florence made landfall near Wrightsville Beach, North Carolina, on September 14, 2018, RMS began monitoring the situation on the ground. Due to the significant rainfall in the region, major flooding ensued, blocking many roads and creating hazardous conditions for travel. RMS waited a few extra days before sending a small group of engineers and modelers into the affected region.
Tree fall was prevalent throughout the region from Charleston, South Carolina, up to the North Carolina barrier islands near Morehead City and inland for quite some distance, due to the significant amount of rain and the slow speed at which the storm moved once it made landfall. The damage to buildings caused by tree fall varied depending on the area. For example, in South Carolina the RMS team saw few trees that fell onto houses, but in parts of North Carolina, the number of trees falling on homes was significantly higher, even though only a small percentage appeared to have caused significant damage.
Figure 2: Tree fall examples in North Carolina
One common failure observed in the Carolinas immediately after Hurricane Florence was to vinyl siding. This type of wall cladding is common in this area and did not perform well, even though the wind speeds experienced in Florence were below the design wind speeds.
Figure 3: Vinyl siding damage was common in the Carolinas
The performance of asphalt shingles was closely linked to their age. Visibly older roofs often had shingle failures, while younger roofs in the same local area were not visibly damaged. Clay tile roofs are not common in the Carolinas, and of the small number of them observed by the team, most had at least a few tiles broken or displaced. Consistent with observations from previous storms including Hurricane Irma in Florida in 2017, was the superior performance of standing seam metal roofs. The RMS team in the Carolinas did not observe any standing seam metal roofs which were visibly damaged.
Figure 4: Roof damage to asphalt shingle and tile roofs
Hurricane Florence brought both coastal storm surge and significant inland flooding. The RMS team captured some of the damage from both of these destructive water events. Most notable was that storm surge impacts seemed to be muted by the large sand dunes along parts of the North Carolina coast including Atlantic Beach.
Both storm surge and inland flooding were significant in New Bern, North Carolina. The team estimated approximately ten feet of surge in some coastal areas as well as ten feet of inland flooding in parts of the town. Flood damage is more commonly indicated by large piles of debris and contents that have been placed along the roadsides.
Figure 5: RMS engineer recording flood water depth after Hurricane Florence
Figure 6: Flooded multi-family housing in Piney Knoll Shores, North Carolina. The water reached up to the door handle and these buildings were tagged as unlivable. Most of the contents had been piled in the driveway for disposal.
Figure 7: (left) A home in Pollocksville, North Carolina was flooded up to the second story floor; (right) Foundation damage to commercial properties in Pollocksville.
Figure 8: Two neighboring houses in New Bern, North Carolina. One has an elevated, occupied first floor and was not damaged (right); the other (left) had a minimal first floor elevation above ground and was severely damaged.
Comparison with Hurricane Matthew
Hurricane Florence impacted some of the same areas in the Carolinas that were affected by Hurricane Matthew in 2016. The RMS team was able to visit a few of the same buildings damaged by Matthew to see how they fared with Florence. In some areas, Matthew caused more wind and/or surge damage than Florence and in other areas the reverse was true.
Figure 9: The same structure after Matthew (left) and Florence (right). After Matthew, the cladding on the chimney was replaced, and it looks like some of the shingles were replaced. With Florence, there was minimal to no damage. Another observation is the use of window opening protection (plywood) for Florence which was not observed after Matthew.
Figure 10: The same location after Matthew (left) and Florence (right). In Matthew, the home suffered cladding damage. After Florence (right) there is no damage to the new cladding, but there is damage to the ceiling underneath the first floor.
Figure 11: The same location on Oak Island, North Carolina after Matthew (left) and Florence (right). In Matthew, there was significant surge damage and several feet of sand deposited. In Florence, no significant flooding effects, but the adjacent house had severe vinyl siding damage.
Figure 12: A hotel on Oak Island after Matthew (left), when the hotel was still open; after Florence (right), the hotel was closed due to significant water damage (notice the dumpster full of wet carpet).
With the RMS damage reconnaissance team visiting the Carolinas a few days after Hurricane Florence impacted the region, the information gathered helps us understand the extent of the damage as well as its frequency and severity. While Florence did cause some wind damage, most of this damage was minor, but in some cases, minor to moderate wind damage had caused significant water intrusion and interior damage. Flooding damage was significant in some areas impacted by Florence, both by storm surge and inland flooding from excessive rainfall.
Each hurricane is unique in its impact at landfall. By having boots on the ground soon after landfall, RMS is able to observe any unique or uncommon damage as well as damage “themes” that are consistent across multiple events in different regions. All of this helps inform the collective knowledge within our model development group to improve, calibrate, and substantiate our building vulnerability functions and damage models.