Octa's transportation blog

Irvine Ranch Conservancy Completes Two Restoration Projects with OCTA

This article originally appeared in the Fullerton Observer.

Irvine Ranch Conservancy (IRC) is pleased to announce the successful completion of the Agua Chinon and Silverado habitat restoration projects. These projects enhance riparian or streamside habitats to benefit various common and rare wildlife species. Both projects are sponsored by the Orange County Transportation Authority (OCTA) with Renewed Measure M Freeway Environmental Mitigation Program funding. This program provides approximately $10 million to fund 12 habitat restoration projects for nine different entities in Orange County, covering almost 400 acres.

The Agua Chinon and Silverado projects cover 6.1 and 28.5 acres of riparian habitats, respectively. The nearly 10-year process of restoration involved replacing non-native, invasive weeds with a diverse mix of native wildflowers, shrubs, and tree species carefully selected to thrive in these locales. Agua Chinon Wash is part of the San Diego Creek Watershed, and the site is 1.5 miles downstream of the famous “Sinks” geologic landmark. Silverado Creek is part of the Santa Ana River Watershed, and the site is 2.5 miles upstream from Irvine Lake.

“Riparian habitats are perhaps the landscape’s most sensitive and ecologically important parts. Working on these OCTA-funded projects, reconnecting fragmented landscapes, restoring wildlife corridors, and enhancing ecological functions was a privilege. These projects and the OCTA-funded Bee Flat project have enabled IRC to conduct large-scale, seed-based restoration that we had previously tried only at small sites. We also credit the Wildlife Agencies for their willingness to support some innovative approaches to restoration,” says Robert Freese, IRC Restoration and Enhancement Program Manager.

Both projects experienced significant challenges over the years. The dry sandy soils of Agua Chinon meant that shrubs and trees grew slowly. However, wildflowers proliferated, and the site soon became a destination for viewing early spring wildflowers. Then Agua Chinon burned in the 2020 Silverado wildfire and suffered sediment and debris flows for the next two years, which smothered vegetation. This was the ultimate test of ecosystem resilience, but with the wet winter of 2022-2023, the native vegetation rebounded strongly. The Silverado site presented other challenges, including installing over 11,000 container plants into the stony soil of the floodplain. Wildlife frequently damaged the drip tubing used to irrigate these plants. Flooding brought new influxes of weeds to the site each year. IRC staff cultivated a dense shrub canopy to suppress such weeds in the future and will continue to patrol the site to remove high-priority weed species.

Staff from the Wildlife Agencies (U.S. Fish and Wildlife Service and the California Department of Fish and Wildlife) inspected these sites. It evaluated monitoring data before certifying that the projects met all standards for ecological performance. Additionally, the US Army Corps of Engineers certified that the Agua Chinon project met their landscape, geomorphic, and biological functions criteria. This review process resulted in both projects being deemed fully successful and complete.