The Tijuana River Reserve is advancing a decades-long effort to answer one not-so-simple question: What are we going to do about sediment along the South California coast?

Moved by rivers, currents, storms, and other processes, sediment is an unglamorous but fundamental driver of the shape, stability, and appearance of the region’s coastal areas and habitats. Yet as the coast becomes more urbanized, the supply and flow of sediment has become increasingly impacted by human activities.

“Sediment has long been viewed as a contaminant, or something to be ‘dealt with,’ and often it is just dumped offshore at deep ocean sites or trucked off to landfills,” says Kristen Goodrich, the Reserve’s Coastal Training Program Coordinator. “But it’s actually a critical natural resource that we need to view as beneficial.”

For example, in some cases, sediment can be used to help maintain marsh elevation relative to sea level rise, grade developments, or to build up beaches and dunes and promote living shorelines through practices like beach nourishment and thin-layer augmentation. Local sources of sediment are more sustainable than those transported or slurried from distant locations, however, in many places, the beneficial reuse of locally-derived sediment remains unfeasible.

Goodrich partnered with researchers from the University of California Irvine and the Southern California Coastal Water Research Project to study barriers and opportunities to the beneficial reuse of sediment. Their findings, published in Ocean & Coastal Management, outline opportunities for systemic changes to encourage the beneficial reuse of sediment to support coastal resilience in Southern California.

The research team found regulatory inflexibility to be a significant obstacle to reuse, as federal, state, and local agencies often have different, sometimes incompatible, permitting requirements and processes. Reuse also can be restricted by technical challenges associated with matching sediment types between dredging sites and the sites where sediment is needed. Even psychological aspects come into play, such as public perceptions that sediment placement may damage the attraction or health of the placement site.

The team presented several recommendations to address barriers like these, some of which are already being tested by managers in the region. These include streamlining the permitting process, training and education, and incorporating the financial benefits of sediment reuse into project planning. In a subsequent paper in Shore & Beach, Goodrich and colleagues—representing perspectives from coastal sediment management organizations in California—called for improved regional sediment management, as well as increasing organizational capacity and coordination.

“We need to work together as a region to effectively manage our sediment for the future of our coasts and wetlands,” says Goodrich.

The Reserve is one of the few sites in California that is experiencing an excess, rather than a shortage, of sediment due to natural erosion processes exacerbated by urban development in its binational setting. This creates a unique opportunity for the Reserve to test and study different approaches to beneficial use and then share the results of these studies for the broader coastal management community. For example, the Tijuana River Estuary Fate & Transport Study showed that fine-grained sediment, when placed in the coastal nearshore, is distributed in ways that reinforce this as a promising beneficial use approach and an alternative to current practices that involve excavation and trucking off-site.

“Right now we have an abundance of sediment, which gives us an opportunity to study beneficial reuse in creative and sustainable ways,” says Goodrich. “But as land use changes in the border region, we could see less sediment carried downstream in the future. As we plan for sea level rise, we want to have protective beneficial use practices understood and in place.”

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