Uncrewed aerial systems (UAS) provide an effective method to examine geomorphic and vegetation change in restored coastal dune ecosystems. Coupling structure-from-motion (SfM) photogrammetry with RGB orthomosaic imagery allows researchers to characterize spatial-temporal geomorphic responses associated with differences in vegetation cover. Such approaches provide quantitative data on landscape morphodynamics and sediment erosion and deposition responses that allow scientists and land managers to assess the efficacy of dynamic restoration efforts and, in turn, make informed decisions for future restoration projects. Two different restored coastal foredune sites in Humboldt County, California were monitored between 2016–20 with UAS (quadcopter and fixed-wing), kite aerial photogrammetry (KAP), and terrestrial laser scanning (TLS) platforms. We compared our KAP- and UAS-SfM elevation models to concurrently collected TLS bare earth models for five of our fifteen collections. The goal of this study was to inform on the potential of a multi-platform aerial approach for calculating geomorphic differences (i.e., topographic differencing), in order to quantify sediment erosion and deposition, and vegetation change over a coastal dune ecosystem. While UAS-SfM datasets were relatively well fit to their TLS counterparts (2.1–12.2% area of difference), the KAP-SfM surfaces exhibited higher deviations (23.6–27.6%) and suffered from systematic collection inconsistencies related to methods and susceptibility to external factors (e.g., the influence of wind speed and direction on variable altitude, image overlap, and coverage extent). Finally, we provide commentary on the logistical considerations regarding KAP and UAS data collection and the construction of uncertainty budgets for geomorphic change detection (GCD), while providing suggestions for standardizing methods for uncertainty budgeting. While we propose an approach that incorporates multiple levels of collection- and processing-based uncertainty, we also recognize that uncertainty is often project-specific and outline the development of potential standards for incorporating uncertainty budgets in SfM projects.

The Lanphere Dunes, part of the Humboldt Bay National Wildlife Refuge, has been the focus of foredune restoration efforts since the 1980s. Efforts have centred around removal of an invasive European beach grass species, Ammophila arenaria, introduced in the early 1900s to stabilize the dunes to protect landward communities from coastal flooding and storm surges. Despite effectively stabilizing the foredune, A. arenaria forms monotypic vegetation stands, with highly dense roots, rhizomes, and above-ground biomass that can lead to pronounced scarping of the seaward slope, alongshore steering of wind and sediment, a lack of landward transfer of sand, and a steeper, more peaked profile.Effective foredune restoration must consider the coupled interactions between dominant plant type and the geomorphic processes that influence dune form. A 5 ha reach of recently restored foredune was monitored biannually with terrestrial laser scanner and uncrewed aerial systems platforms between 2015 and 2021 to characterize the impacts of dynamic restoration on foredune form and resiliency. This reach included two control plots: (1) native, non-restored and (2) invasive, and three restored plots revegetated with native species: (3) a native grass (Elymus mollis), (4) a low-lying herb and subshrub assemblage, and (5) a mixture of the native grass, herbs, and subshrubs.After five growing seasons, restored plots exhibited distinct geomorphic and sediment budget differences. Natively vegetated plots recovered from extensive scarping 2 years faster than the invasive plot. Restored plots saw foredune height (0.5-0.7 m) and width increase, landward extension (1 m) while maintaining a similar seaward position, and positive lee-slope sediment budgets that exceeded both control plots (up to 0.015 m 3 m À2 month À1 ). These results suggest that the native vegetation plots allowed increased landward sand transport across the foredune, and increased the capacity of the foredune to recover more quickly following dune scarping.

The Oceano Dunes near Pismo Beach, California is part of a large transgressive dune system that extends up to 5 km inland and hosts a state park that has been managed for off-highway vehicle recreation since 1982, although vehicle activity has existed in the dunes for almost 90 years. As a result, foredunes have been largely obliterated and sand surfaces in vehicle use areas are highly emissive of dust-sized particles, causing frequent exceedances of state air quality standards. To reduce dust emissions from the dunes, a nature-based foredune restoration strategy using five different treatments over a 20-ha site was implemented in February 2020.The research hypothesis is that treatments will differ in their ability to promote deposition and dune development and that more intensive planting-based treatments will outperform simpler treatments. We test this using biannual highresolution uncrewed aerial system (UAS) surveys to quantify sediment budgets, sand exchanges between beach, foredune, and backdune components, changes in plant cover, and related dune development over a 2-year period (October 2019-2021).After two full wind and plant-growth seasons, results show that all treatments are maintaining a positive sediment budget (net accumulation), most are developing sizable nebkha dunes (an important stage in foredune development in this region), and some are increasing plant cover and species richness. There is no clear winner, yet two treatments (broadcast native plant and sterile grass seeds, and a highdensity straw planting node with native seedlings) are performing well toward developing an incipient foredune. These results will inform an adaptive management process that could entail further modifications to enhance foredune development. Based on this experience, and with reference to other types of restoration projects, we refine existing criteria used to assess the performance of "dynamic" dune restoration efforts to include settings that involve revegetation (vs. devegetation) as a means for foredune re-establishment.

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