On June 24th, Champlain Towers South, a 13-story beachfront apartment building in Surfside, Florida, collapsed and left nearly 100 dead. The response by Miami-Dade County has been admirable: the fire department tirelessly searched in dangerous conditions for missing loved ones, mayor Daniella Levine Cava directed the county Department of Regulatory and Economic Resources to audit all at-risk buildings in the next month, and the community has come together to mourn the victims of this tragedy. We stand with the county in supporting the community and the loved ones of the people yet to be found.
One question has been at the forefront of everyone’s minds: why did the building collapse? This tragedy raises questions about how sea level rise could play a role in more building collapses throughout the nation over the coming decades. While the collapse at Surfside is believed by some sources to be due to site-specific factors like construction quality, we wanted to explore three additional reasons why sea level rise could increase the risk of building collapse.
3 reasons sea level rise could impact structural stability.
- Sea level rise causes saltwater intrusion into groundwater.
- Soil becomes weaker as it becomes saturated by a rising water table.
- Erosion could remove the foundation around a shoreline property.
As the sea rises, the difference between the high sea level and relatively low water table causes saltwater to infiltrate the groundwater, raise the water table, and impact building foundations in two ways. Firstly, a rising water table can cause water to seep into basements designed for a lower water table. Secondly, the salty water entering the basement causes corrosion of the steel rebar in reinforced concrete. This is problematic because saltwater corrodes metal five times faster than fresh water.
Once water starts seeping into a basement, property owners will need to continuously pump water out. If steel comes into contact with salt water, it begins to rust. When steel rusts, it expands and causes the surrounding concrete to crack and break off – a process known as “spalding.” If the steel rebar in reinforced concrete gets weaker, then the concrete will have less resistance to bending. Furthermore, if pieces of concrete break off, the concrete will also have less resistance to compression. Reinforced concrete columns with compromised strength in compression and bending would significantly increase the risk of a building collapse.
The underground parking garage at Champlain Towers South displayed significant water damage, soon to be a common occurrence in high-risk sea level rise regions.
A rising water table could also cause the sediment around a foundation to weaken. Think of it this way: trees rely heavily on their roots, or foundations, to stay upright. After heavy rain, trees are more likely to uproot during strong winds because the sediment around their foundation has lost effective strength, or its ability to hold objects in place. It’s not normal to see buildings topple over like trees during big storms, and it’s probably less likely we’ll see this failure mechanism, but the risk of this dramatic failure does increase with a combination of wet soil conditions and inadequate foundation design.
Fallen trees with exposed roots like the one above are common occurrences when the sediment around it has heavy water saturation. Weak, wet sediment makes for weak foundations.
Finally, the shoreline recedes inland when sea level rises, so building collapse could be caused by visible erosion around the foundations of waterfront structures. Walk into the water at different beaches and you’ll notice that some get deep quickly, while others are shallow. The vertical profile of a beach is shaped by the sediment and its exposure to forces from waves and currents. As water rises, the forces change and the sediment shifts to find a new balance, or “equilibrium.” Coastal engineers sometimes use a heuristic known as the “Bruun Rule,” where 1” of sea level rise translates to roughly 100” of shoreline movement. This means that a rising sea will increase erosion and threaten to remove the sediment around the foundations of waterfront buildings.
Many along the coast attempt to fight erosion with grey infrastructure like revetments or seawalls. While these hard infrastructure solutions can reduce erosion in the short-term, it could transfer the risk elsewhere. Simply put, the water has to go somewhere. Reducing erosion in one location could increase erosion at a nearby, unprotected place. Some municipalities are aware of this risk transfer, and make it difficult for owners to get permits to protect their property. These owners find themselves in an impossible position, where they’re unable to protect their homes and investments.
How can we mitigate the risk?
Sea level rise makes it difficult to permanently draw a line between the land and sea. It’s inevitable that the risk of flooding and building collapses will increase over the coming decades in every shoreline community. So what do we do next? In addition to implementing traditional mitigation measures, like levees, or experimenting with nature-based solutions to mitigate flooding, retrofitting buildings needs to be included as an adaptation measure for sea level rise. Since private buildings support essential services (like schools, law enforcement, and infrastructure) through property tax revenue, it’s essential that communities start to invest in mitigation measures that protect individual buildings.
To reduce the risk of building collapse, we should use corrosion-resistant materials for rebar in new construction, while also redesigning and rebuilding the foundations of existing buildings. And to reduce the risk of flooding in buildings, we can lift them onto the redesigned and rebuilt foundations, because increasing the elevation of a building is the most effective way of reducing flood risk.
HighTide is committed to helping plan for a future with sea level rise. We’d be more than happy to provide your community with the bottom line for what it’ll cost to adapt, and what the risk reduction is worth. All you have to do is get in touch.