Adaptation Planning to Mitigate Coastal-Road Pavement Damage from Groundwater Rise Caused by Sea-Level Rise
Sea level in coastal New England is projected to rise 3.9–6.6 ft (1.2–2.0 m) by the year 2100. Many climate-change vulnerability and adaptation studies have investigated surface-water flooding from sea-level rise (SLR) on coastal-road infrastructure, but few have focused on rising groundwater. Groundwater modeling in New Hampshire’s Seacoast Region has shown that SLR-induced groundwater rise will occur three to four times farther inland than surface-water flooding, potentially impacting 23% of the region’s roads. Pavement service-life has been shown to decrease when the unbound layers become saturated. In areas where groundwater is projected to rise with SLR, pavements with groundwater 5.0 ft (1.5 m) deep or less are at risk of premature failure as groundwater moves into the pavement’s underlying unbound layers. In this study, groundwater hydrology and multi-layer elastic pavement analysis were used to identify two case-study sites in coastal New Hampshire that are predicted to experience pavement service-life reduction caused by SLR-induced groundwater rise. Various pavement structures were evaluated to determine adaptation feasibility and costs to maintain the designed service-life in the face of rising groundwater. This investigation shows that relatively simple pavement structural modifications to the base and asphalt concrete (AC) layers of a regional corridor can eliminate the 80% to 90% service-life reduction projected with 1.0 ft SLR (year 2030) and will delay pavement inundation by 20 years. Pavements with adequate base-layer materials and thickness require only AC thickness modification to avoid premature pavement failure from SLR-induced groundwater rise.
Sea-level rise (SLR) can cause erosion and storm-surge damage, flood coastal communities, and damage coastal infrastructure (1). Many studies have investigated SLR-induced surface-water flooding and storm surge on road infrastructure (2, 3) but few have investigated the effect of SLR-induced groundwater rise on coastal-road pavement systems. As groundwater rises, the unsaturated zone decreases (4) and groundwater will impact roads, septic systems, underground utilities, and foundations in areas where the groundwater is currently near the ground surface (5).
The effect of rising groundwater on pavement performance has been investigated. Full-scale pavement tests conducted in Florida test pits found a more than 50% reduction in the resilient modulus of granular subgrade layers when the groundwater table rises 24 in. (61 cm) to the bottom of the base layer (6). A study of SLR and increased precipitation on roads along the Gold Coast in Australia found that approximately 1.9 miles (3.0 km) (32%) of roadway will be at high risk of failure by 2070 when groundwater is predicted to be less than 3.3 ft (1.0 m) below the pavement surface (7). Similarly, SLR-induced groundwater rise was found to reduce coastal-road pavement life by 50% from fatigue-cracking distress, and by up to 90% from rutting distress when groundwater moves into the pavement base layers (8).
Climate-change adaptation studies assess the vulnerability of assets, choose appropriate climate-change scenarios, identify adaptation strategies, and recommend actions that may be robust or flexible (9). Studies have shown that some pavement structures are more resilient to rising groundwater than others (10, 11), but to date, no studies have quantified the cost and benefits of strategies to mitigate pavement impacts from SLR-induced groundwater rise. The implementation of targeted adaptation actions to vulnerable coastal-road infrastructure will save money through damage avoidance (8).
The objective of this research was to identify pavement structures that will preserve pavement service-life in the face of SLR-induced groundwater rise. It provides a quantitative assessment of pavement strains for projected groundwater levels and compares service-life reductions in terms of fatigue and rutting across different pavement structures. Pavement construction costs and road-surface elevations were evaluated to determine cost-effective strategies to prevent premature pavement failure as rising groundwater weakens the pavement supporting layers and inundates the pavement surface. Whereas rising temperatures may also weaken pavements (12), this investigation considered only the effects of SLR-induced groundwater rise on pavement service-life. Fatigue cracking and rutting were evaluated independently, and it was assumed that no pre-existing distresses existed in the pavement evaluation sites. In reality, these distresses are coupled and exist to some degree in the pavement structure; consequently, pavement failure will likely occur sooner than predicted in this analysis. SLR-induced groundwater-rise projections are limited to the SLR scenarios chosen for this study.
Earth Systems Research Center
Transportation Research Record: Journal of the Transportation Research Board
Digital Object Identifier (DOI)
Knott, J. F., J. S. Daniel, J.M. Jacobs, and P. Kirshen. 2018. Adaptation Planning to Mitigate Coastal Road Pavement Damage from Groundwater Rise caused by Sea-Level Rise. TRB Research Record: Journal of Transportation Research Board. 0361198118757441.