Purpose of the project: Removing dams and other barriers to passage in the coastal rivers of southern California is one of the most important and effective ways to aid in the recovery of endangered Southern California Steelhead (SCS) trout and other threatened species like the Arroyo chub and Arroyo toad. Removing these dams provides benefits up and downstream of the removal site. Barrier remediation improves access to spawning and rearing habitat and restores gravel and sediment transport downstream. Restoring sediment transport has long-range benefits of increasing habitat quality and facilitating sediment transport to beaches and estuaries to prevent coastal erosion. These key ecosystem services far outweigh the relatively low cost of removing these dams and barriers, for example, the headwaters of Trabuco Creek contain high-quality spawning and rearing habitat for endangered Southern Steelhead, so removing these small dams is an important step in preparing for steelhead migration to this habitat upon removal of two large fish passage barriers in the lower watershed.
Purpose of the project:
Removing dams and other barriers to passage in the coastal rivers of southern California is one of the most important and effective ways to aid in the recovery of endangered Southern California Steelhead (SCS) trout and other threatened species like the Arroyo chub and Arroyo toad. Removing these dams provides benefits up and downstream of the removal site. Barrier remediation improves access to spawning and rearing habitat and restores gravel and sediment transport downstream. Restoring sediment transport has long-range benefits of increasing habitat quality and facilitating sediment transport to beaches and estuaries to prevent coastal erosion. These key ecosystem services far outweigh the relatively low cost of removing these dams and barriers, for example, the headwaters of Trabuco Creek contain high-quality spawning and rearing habitat for endangered Southern Steelhead, so removing these small dams is an important step in preparing for steelhead migration to this habitat upon removal of two large fish passage barriers in the lower watershed. These downstream total barriers at the Metrolink and Interstate-5 bridge arrays are in advanced design for remediation as technical fish passage solutions and are located close together on lower Trabuco Creek, the largest tributary to San Juan Creek in San Juan Capistrano, Orange County. This coast-to-headwaters approach to restoration not only implements the federal recovery plan for endangered Southern steelhead but provides community benefits that exemplify the power of fish habitat partnerships.
Trabuco District Dam Removal Project
In 2014, the Cleveland National Forest (CNF) initiated an effort to restore the migratory corridors for fish and other aquatic species in the San Juan and Santiago Watersheds by removing the remnants of small (approximately 2 – 15 ft) dams constructed by Orange County (California) between 1940-70s. These dams were originally built to create pools for a stocked rainbow trout fishery and recreational use. However, in addition to restricting passage to aquatic species and degrading habitat, many also pose potential public safety hazards to flooding during flashy high flow events that are often associated with rain events in the region.
This project, known as the Trabuco District Dam Removal Project, focuses on four creeks (Silverado, Holy Jim, Trabuco, and San Juan) and has nearly completed the removal of 81 check dams. This project will also remove or replace four impassable road crossings on forest lands. The project spans stream segments totaling approximately 4.75 miles and is being carried out in phases along each stream to limit downstream impacts from sediment release and/or risk to infrastructure integrity. Depending on site location and accessibility, CNF is using a variety of methods, some traditional such as utilizing hand crews, pneumatic or gas-powered drills, and jackhammers, as well as some more creative approaches such as using a specialized Walking/Spider excavator sites with limited access, or tapping into the explosives expertise (and available manpower) from the US Marine Corps (USMC) located at neighboring Marine Corps Base Camp Pendleton.
The CNF’s innovative approach to this project is not limited to the methods of dam removal, but also in how they approached the environmental permitting process. CNF was able to streamline the National Environmental Policy Act (NEPA) compliance process for this project. Taking a watershed-scale approach and evaluating all 81 of these small dam removals in one environmental assessment (EA) allowed for a quicker and cost-efficient review, and allowed for flexibility in the timing and methods of removals. This programmatic approach to permitting has the potential to be replicated by other projects, and ultimately lead to more dams being removed more quickly, and increasing access to additional and higher quality habitat.
Monitoring Small Dam Removal Effectiveness in Southern California
In 2014, a study was initiated by NOAA (Restoration Center) in collaboration with USFS and other partners including the California Conservation Corps’ Veterans Corps Fisheries Program, California Department of Fish & Wildlife (CDFW), University of California Los Angeles and Santa Barbara, US Forest Service (USFS), Pacific States Marine Fisheries Commission (PSMFC), and the California Fish Passage Forum (via support from NFHP and AFWA from a Multi-State Conservation Grant) to monitor the effectiveness of small dam removals in the region. This study was integrated into the Trabuco District Dam Removal Project, in response to a recognized gap in the scientific literature pertaining to dam removal knowledge in Southern California to support endangered steelhead recovery, The study continued through 2019 and analyzed the impacts on steelhead habitat under a range of regulatory and climatic conditions (fire, drought, and flood - all of which occurred during the study period) in three priority steelhead watersheds in Ventura, Los Angeles, and Orange Counties (the later included monitoring of dams being removed as part of the Trabuco District Dam Removal Project in the San Juan Watershed).
The study captured pre-dam removal data to better understand the influences of sediment released by a small dam on streambed morphology under differing regulatory constraints throughout Southern California, employing cost-effective long-standing methodologies to:
• Understand the hydrologic context Southern California streams face under extended drought conditions;
• Examine elevation change in streambeds after dam removal to understand its influence in changing habitat features;
• Evaluate stream substrate quality in response to small dam removal.
This study illustrates the value of pre-dam removal data. Utilizing baseline pre-dam removal data, the conclusion that a cyclical pattern of sedimentation and infilling occurred under drought conditions (2014-2016) was supported, in favor of an alternate explanation that this sedimentation deposition in later years was due solely to dam removal. Thus, this study demonstrated an important phenomenon in stream restoration ecology that sediment quality improved immediately after dam removal with flushing of fine sediment (even under drought conditions) for improved habitat quality for aquatic species.
Human Interest/Community Benefit:
Removing small, often obsolete, dams like these not only benefit fish and aquatic habitat and increases resiliency, but also helps ensure public safety by reducing potential flooding hazards.
Each of these projects demonstrated innovative collaborations between partners, such as the CNF’s collaboration with the USMC during implementation to utilize their unique expertise using explosives to remove some of these small dams, and other partners in a post-dam removal assessment. This project is also part of the broader South Coast Steelhead Coalition effort, led by CalTrout in partnership with Trout Unlimited, which brings together >35 federal, state, local agencies, tribal nations and environmental groups to implement steelhead recovery and community benefit projects in the four highest priority rivers in San Diego, Orange and Riverside counties, such as San Juan Creek.
Project Timeline:
2014 – CNF initiated work removing small dams in the San Juan and Santiago Watersheds.
2014 – Monitoring by NOAA/California Conservation Corps Veterans Corps and PSMFC of small dam removal effectiveness began
2019 – As of September 2019, 71 dams had already been removed or remediated
2020 - The CNF plans to complete the project by removing dams in Holy Jim Canyon (once again working with the US Marine Corps), as well as continuing work with their Spider Excavator contractor in Trabuco Canyon.
Economic Calculator results*:
Jobs: 0.7517
Total Sales: USD 80,457.13
Value Added: USD 43,822.14
Income: USD 34,683.54
*for Small Dams Effectiveness Monitoring Project only
Partners:
The development, implementation and/or funding of both of these efforts has been supported by the following partners:
• American Conservation Experience
• NOAA/California Conservation Corps Veterans Corps Fisheries Program
• California Department of Fish & Wildlife
• California Fish Passage Forum
• Caltrans
• Federal Highway Administration
• National Oceanic & Atmospheric Administration Restoration Center
• Orange County Parks
• Orange County Transportation Authority
• Pacific States Marine Fisheries Commission
• US Fish & Wildlife Service
• US Forest Service (Cleveland National Forest – Trabuco Ranger District)
• US Marine Corps
• University of California Los Angeles
• University of California Santa Barbara