In the study, scientists examined a beach nourishment project at Benson Beach, just north of the mouth of the Columbia River at the Washington/Oregon border, where dredged sand from a nearby engineered inlet was placed on the beach as a beneficial use of dredged sediment.

Although much of the newly placed sand eroded within two weeks, researchers found that it likely remained within the coastal system, where it continued to supply sediment to the beach and help protect nearby dunes. 

Beneficial use of dredged sediment 

The nourishment project took place along one of the most energetic stretches of coastline in the Pacific Northwest. Field observations of the placement site found that the newly placed dry beach sand eroded rapidly, over the course of two weeks—this during a period of moderate wave activity with no major storms.

Rather than leaving the nearshore environment entirely, much of the dredged sediment was transported just offshore and deposited around the beach's inner sandbar, a submerged component of the coastal sediment system.

Because the sand stayed within the nearshore environment, it remains available to move back toward the beach under future wave conditions. In effect, the beach nourishment shifted location rather than leaving the system altogether.

The modeling also indicated that while little of the nourishment remained on the upper beach, it acted as a protective buffer that reduced erosion of the adjacent dune system.

These dunes provide natural protection for inland areas by absorbing wave energy during storms. Even though the nourishment eroded rapidly from the upper beach, modeling suggests that its temporary presence helped shield these valuable coastal landforms. 

Improving future beach nourishment efforts