Adding Sand to Enhance Texture or Quantity

In the face of rising sea levels due to climate change, natural or living shoreline projects are gaining traction as a means to build resilience against the encroaching tides. One such region embracing this approach is San Diego County, where the evolution of beach nourishment projects has been a subject of interest.

A recent study, published in the journal Coastal Engineering, analyses four beach nourishment projects in the county to understand sand movement. The research was conducted by scholars at the University of California San Diego, with funding from the United States Army Corps of Engineers, California Department of Parks and Recreation, Division of Boating and Waterways, National Science Foundation, and California Sea Grant. Katherine Leitzell, associated with California Sea Grant, is also linked to the project.

The study utilised ATVs, jet skis, and other tools to conduct regular surveys of each beach for over a decade, resulting in the creation of elevation maps. These maps provided researchers with a unique opportunity to assess how the beach changed over time.

One of the key findings of the study was the impact of sand grain size on movement. Larger grains travelled further and faster along the coast, with the sand placed on Torrey Pines beach north of San Diego washing away in a single storm in 2001. Conversely, smaller grains tended to stay put, offering a potential solution for more effective beach nourishment projects in the future.

The sand moved both north and south along the coast, and in 2016, it contributed to the closure of the Tijuana River estuary. These insights are crucial for planning and executing future beach nourishment projects, particularly in North San Diego County, which is planning a 50-year, $160-million series of beach nourishments to combat flooding and erosion.

It's important to note that California has been adding sand to beaches for decades, with many wide sandy beaches artificially created by the addition of sand dredged from harbors or other construction projects. However, dams and cliff stabilisation projects have reduced sand contributions from these sources.

The study also highlights the importance of replenishing beach sand, as the ocean continually makes "withdrawals" from the beach sand "bank account." If sand is not replenished, beaches will disappear. This is evident in the case of Imperial Beach, where the equivalent of 138 Olympic-sized swimming pools of sand was added in fall 2012, only to lead to unintended consequences.

Predicting or modelling the evolution of beach nourishment projects is currently challenging, but the observations in this study provide a good initial indication. The study's findings could pave the way for more sustainable and effective beach nourishment strategies, ensuring the preservation of California's beloved coastline for generations to come.