Remote sensing of beaches: using satellite and airborne platforms to characterize a century of change in Orange County, California

Abstract:

The sandy beaches of Southern California are a focal point of the region’s entertainment industry and tourism economy, protect development and wetlands from coastal flooding and erosion, and enhance the quality of life of millions of people through recreational activities and access to the ocean. Southern California beaches were not naturally wide, but during the 20th century, many beaches were significantly widened as a result of harbor development and deliberate placement of dredged material in the nearshore (Flick 1993). Furthermore, beach width has been sustained for decades at many sites through beach nourishment projects (Flick 1993). However, decline in beach nourishment activity is resulting in beach loss, and recent modeling points to the complete loss of 2/3rds of southern California beaches by 2100 as a result of sea level rise (Visousek et al. 2017). Herein, aerial imagery from the early 20th century is combined with satellite imagery over recent decades as well as high resolution Unmanned Aerial System (UAS) data over the past year to yield a century of temporal change in beaches along the 42-mile Orange County coastline of California. Aerial and UAS imagery is manually processed while satellite imagery is processed using CoastSat (Vos et al. 2019). Observed increases in beach width can be linked to human activities such as harbor dredging as well as major storm events that episodically deliver large volumes of sediment to the coast, while decreases in beach width can be linked to periods of drought and episodes of energetic storm systems. The spatial and temporal impact of coastal structures is also evident in beach width changes. We report on the utility of satellite systems, traditional aerial systems and UASs for beach width monitoring (resolution, spatial extent, sampling frequency, cost) along urban coastlines such as Orange County, California. Here, long-term monitoring data is needed to improve sediment management including the beneficial reuse of sediment for coastal resilience (Ulibarri et al. 2020).

References

Flick (1993). Shore and Beach, 61(3).

Ulibarri et al. (2020) Ocean & Coastal Management. Article in Press.

Vitousek et a. (2017) Journal of Geophysical Research: Earth Surface, 122(4), 1060-1067.

Vos et al.(2019) Coastal Engineering. 150, 160–174.