RECOVERY OF FOREDUNES BY AEOLIAN REBUILDING FOLLOWING THE 2015-16 EL NINO, LANPHERE DUNES,CALIFORNIA, USA

Sandy coastlines are under increasing pressure from rising sea levels, enhanced coastal erosion, and flooding. Coastal foredunes exist as the seaward most landform along many sandy beaches and serve as the initial line of protection for landward resources, ecosystems, and communities. Foredunes are regularly impacted by erosive events that disrupt onshore sediment transport, foredune evolution, and ecosystem function. Occasionally, anthropogenic intervention is required to help manage and/or restore foredune form and/or function. Though initial restoration efforts centered on dune form stabilization, contemporary practices focus on dynamic restoration of important geomorphic (aeolian) processes that maintain dune function and development.

This study reports findings from ongoing foredune restoration at the Lanphere Dunes in Humboldt Bay National Wildlife Refuge, Arcata, California. Foredunes at the site experienced invasive vegetation (Ammophila arenaria) removal and have been revegetated with different treatments of native vegetation. The working hypothesis is that natively vegetated foredunes are more resilient to natural disturbances, such as wave attack and scarping, and should exhibit faster recovery to pre-disturbance states. Key to recovery is the rebuilding of steep, eroded beach scarps that halt onshore airflow and sand transport required for foredune maintenance. Development of aeolian sand ramps is essential for rejoining the beach to the stoss slope of the dune and re-establishing sand transport pathways. The timing and morphodynamics of this rebuilding process are poorly understood.

Biannual terrestrial laser scan campaigns and traditional transects from 2015-19 document and quantify sand ramp recovery and foredune evolution at the site following the erosive 2015-16 El Nino season. Statistical change detection comparing digital elevation models show continued recovery of the sand ramp through slumping processes and aeolian sand ramp development that re-establish onshore sand transport into the lee by 4-6 months. However, this observed trend is only apparent where native vegetation has been restored and not where Ammophila arenaria is present. These trends suggest dynamic foredune restoration at Lanphere is resulting in faster recovery of sediment transport pathways.