Hidden Benefits: How “Lost” Dredged Sand Continues to Shield the Pacific Northwest Coast
New research into coastal management reveals that sand placed on beaches during nourishment projects may be more effective than initial appearances suggest. While much of the material often washes away from the shoreline within weeks, a study focusing on Washington’s Benson Beach suggests this sediment remains a vital asset to the regional coastal system.
The study, titled Beach Nourishment Morphodynamics in a High-Energy U.S. West Coast Environment, examined the practice of “beneficial use,” where sediment dredged from navigation channels—which would otherwise be dumped far offshore—is instead repurposed to combat erosion on nearby beaches.
Rethinking Erosion
Maintaining the navigation channel at the mouth of the Columbia River requires the removal of 2 to 4 million cubic meters of sand annually. For this project, researchers tracked how that dredged sand behaved once placed on Benson Beach, one of the most high-energy stretches of the Pacific Northwest coastline.
Within just two weeks of placement, field observations confirmed that the dry sand on the upper beach had eroded significantly, despite the absence of major storms. While this rapid disappearance might traditionally be viewed as a project failure, the study utilized advanced morphodynamic modeling—specifically the XBeach system—to track where the sand actually went.
The data revealed that the sediment had not left the coastal environment entirely. Instead, it had been transported just offshore, settling around the inner sandbar. By remaining in the nearshore system, the sand stays available to be naturally pushed back onto the beach during future wave cycles.
A Natural Defense System
Beyond its potential to replenish the beach later, the study found that the temporary presence of the dredged sand serves a critical immediate purpose: protecting the dunes.
Coastal dunes act as a vital, natural buffer, absorbing the brunt of wave energy during storm events. Modeling indicated that even as the nourishment eroded from the upper beach, it shielded the adjacent dunes from direct wave impact, effectively acting as a sacrificial layer that preserved the integrity of the inland landscape.
A New Standard for Coastal Management
These findings suggest that environmental managers should shift their focus from the short-term presence of sand on the dry beach toward the health of the entire coastal system.
“The findings underscore the importance of evaluating beach nourishment projects based on the movement of sediment throughout the entire coastal system, not just how long sand remains on the upper beach,” the researchers noted.
By combining field measurements with high-fidelity modeling, coastal managers can better predict the lifecycle of dredged materials. This nuanced understanding is essential for building long-term shoreline resilience, proving that when it comes to coastal protection, “eroded” sand may still be doing a significant amount of work beneath the waves.
