Posted on August 22, 2022
Coastal civil infrastructure is vulnerable to the effects of climate change. Hurricane storm surge and coastal flooding can cause significant hydrostatic and hydrodynamic loads on structures while saltwater intrusion (SWI) may lead to deterioration of foundations. The effects of saltwater intrusion due to Sea Level Rise (SLR) on the foundations of buildings and other civil infrastructure is poorly understood.
Abstract
Such damages may not be detected in a timely fashion nor be insured, leading to significant and unanticipated expenses for building owners. In this study, we evaluate the impact of SWI due to various SLR scenarios on the corrosion of reinforcement in foundations of nearly 137,000 residential buildings in low-lying areas surrounding Mobile Bay, AL. We find that the potential for costly damage is significant. Under an extreme SLR scenario, the annual expected repair costs for the foundations of the studied homes may reach as much as US$90 million by 2100.
Introduction
Sea level rise (SLR) is a significant effect of a changing climate1,2. Ecosystems, human settlement, and vital community services in low-lying coastal plains are all threatened by SLR, which impacts about half a billion people globally3. Flooding of coastal lowlands4, as well as damage to marine ecosystems5, the built environment6,7, and marine transportation systems (seaports)8,9 are all consequences of SLR. Furthermore, in roughly 20% of the Earth’s arable land, including coastal regions of the United States, soil salinity is a problem10. Soil salinity may be ascribed to many factors in addition to SLR, including natural buildup, irrigation, land aridity and human activity. Salts are often brought into the soil via a rising water table or sub-surface movement of water within 1–2 m of the soil surface11. According to current estimates, the rise in the groundwater table in coastal areas due to rising sea levels is approximately proportional to the rise in sea level12,13.
Excessive salinity in ground water may cause major problems for local agriculture, foundations of structural systems, roads, bridges, phone lines, water systems and sewers11. For example, some underground utilities (electric, cable, and telephone) in New Orleans were severely corroded due to the effects of seawater inundation from Hurricane Katrina14. Saha and Eckelman15 concluded that by 2055, existing concrete buildings in Boston, MA within 10 km of the coastline might experience chloride intrusion exceeding code-recommended reinforcing bar cover thicknesses. Many other studies have considered the impact of de-icing salts on concrete bridge decks16,17,18,19,20. However, the authors are unaware of any previous studies that have examined potential deterioration of reinforced concrete building foundations in coastal regions due to saltwater intrusion (SWI) brought about by SLR due to climate change.
In a maritime environment, chloride-induced corrosion of reinforcing bars is the main cause of degradation in reinforced concrete components21. Corrosion initiates when a certain concentration of chlorides accumulates on the surface of the reinforcement bars in the concrete element, which is often due to insufficient concrete cover22, as noted in the “Methods” section. Subsequent corrosion of the reinforcement leads to a decrease in structural capacity and, in addition, is usually accompanied by cracking and spalling due to the expansive nature of the corrosion process. If the concrete element is easily accessible, periodic inspections and maintenance often will uncover the problem and permit timely and appropriate repair or rehabilitation of damaged structural components. On the other hand, foundation walls and slabs frequently are partially or completely inaccessible for periodic inspection, in which case their deterioration may not be detected until it is manifested through damage to the superstructure. In such instances, repair or rehabilitation may be very costly. A similar problem may exist in regions of the United States (particularly in the southern Great Plains region) where expansive soils are prevalent. In such regions, buildings are often constructed as slab-on-grade to minimize the need for inspection and the likelihood of costly foundation deterioration.
Figure 1 shows regions of the coastal US that are especially susceptible to sea level rise due to climate change. The Southeast and Gulf Coast are also regions of significant population and economic growth. The coastal region extending from Boston, MA in a southwesterly direction toward Pensacola, FL supports significant industrial infrastructure, with three major seaports and many of the nation’s largest petroleum refineries, chemical and energy corporations, and aerospace and defense industries located on or close to the coast. Construction brought on by urbanization in these regions will be impacted by increases in the ground water table which exposes foundation systems to saltwater intrusion and corrosion.
In this study, we consider the impact of a changing climate on civil infrastructure from a new perspective: the negative impact of SLR on the foundations of buildings and other civil infrastructure caused by SWI. We consider the probable damage to nearly 137,000 residential buildings in low-lying regions within Mobile County, Alabama caused by the influence of the SWI resulting from SLR scenarios on the corrosion of their foundations through the remainder of the twenty-first century. We outline the conceptual framework of our analysis to help readers quickly grasp the most important ideas. The subsequent “Methods” section provides further details on our analytical approaches, while the “Supplementary Information” (SI) goes into greater depth regarding the datasets, figures, and tables that were used in the analysis. Our results show that buildings located 5–10 km away from the shoreline are the most vulnerable under plausible SWI scenarios. We introduce three example risk mitigation planning strategies and illustrate their relative advantages using a life-cycle approach to guide public policymakers in the future. Additional findings of the mitigating techniques are described in the SI S2 and S3.
