ASSESSING THE IMPACT OF BEACH NOURISHMENT ON THE MORPHOLOGY AND SEDIMENTOLOGY OF COASTAL FOREDUNES

Coastal foredunes provide natural protection against severe storms and sea-level rise. Human efforts to combat beach erosion include beach nourishment, a coastal engineering technique that widens beaches through emplacement of externally sourced sediment. Such measures have become ever more urgent due to accelerating sea-level rise and increased storminess. Consequently, quantifying theinteractions between beach nourishment and dune evolution, including feedbacks between nourishment sediment and changes in dune morphology and sedimentology, is essential in designing resilient coastal systems. This study monitored dune sedimentological and topographic changes between March 2023 and May 2024 following a beach nourishment project at ten cross-shore transects across two sites in the northern Outer Banks, North Carolina. These study sites were distinct in their past management: the dunes at Snow Geese (SG) are fully constructed, and the dunes at the US Army Corps’ Field Research Facility (FRF) are unmanaged. The SG dune was contained within the nourishment zone, whereas the FRF dune was located 380 m south of the nourishment. Transect sedimentological samples collected at 4-m intervals revealed that, while dune grain size both within and south of the nourishment was moderately variable during the year of post-nourishment monitoring (0.17–0.58 mm), this was limited to a mean increase in median grain size of only ~0.01 mm when averaged alongshore across the dune profiles at each site. Repeat real-time kinematic GPS topographical profiles indicate that the dune crest height increased at SG by 0.59 m and at FRF by 0.28 m. However, the dune stoss slope at SG lost volume after its construction in April 2023. In contrast, the FRF dune stoss slope accreted ~1 m, despite being outside of the nourishment zone. The beach nourishment influenced sediment dynamics at both sites and appeared to enhance dune resilience by increasing crest height, but its effects on dune morphology and sedimentology are highly variable, with minimal net changes in grain size and mixed outcomes in dune volume change. These results provide insight into the extent to which nourishment affects both adjacent and downdrift dunes and can help guide future engineering strategies that aim to improve the resilience of, and protection afforded by, dunes.