Arroyo Mocho is a one-mile-long earthen flood control channel that was engineered and planted with the goal of creating a functioning natural stream and riparian corridor while maintaining flood control and groundwater recharge capabilities.
Immediately after the installation of approximately 6,000 planting and cuttings, the site was subjected to several years of drought, followed by an extremely wet winter with multiple storms that exceeded 10-year recurrence intervals. These events caused erosion, scour, and deposition that damaged the plantings and jeopardized the performance goals for revegetation success.
Stillwater Sciences was hired to assess the progress of riparian vegetation establishment and provide strategies to help get the site back on track to meet the 10-year post-implementation success criteria.
Stillwater’s findings indicated that only 3% of the original plantings survived but surviving individuals exhibited high vigor and healthy growth rates. Also, in areas of sediment deposition (i.e., newly formed banks and bars), thousands of first-year recruits were established indicating that riparian plant success was correlated to channel geomorphology dynamics.
Our recommendations include strategic replanting only in those areas anticipated to continue being unaffected by scour events, as well as the integration of riparian vegetation dynamics with the site’s geomorphology and engineering into the re-design prior to additional plantings. Additionally, Stillwater will recommend reference site data collection to determine more appropriate canopy cover performance criteria. Finally, a monitoring plan that allows a relatively rapid assessment of riparian plantings is being prepared to assist in future monitoring efforts and the adaptive management of the site.
