General Project Information
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Project Location
Project Description
The California Department of Transportation (Caltrans) proposes to mitigate for aquatic impacts from the construction of the Route 46 Corridor Improvement Project through restoration of 6,300 feet of Centennial Creek in Paso Robles, California. The project includes the restoration and enhancement of wetlands and other waters, removal and/or replacement of culverts, removal of concrete/rock hardscaping and debris, and replanting the area with native species.
Existing Crossing at Centennial Creek
Project Vicinity
Two phases are proposed for this project. Outstanding mitigation from the Union, Whitley 2A, Whitley 2B, and Cholame sections can be accommodated at Centennial Creek in Phase 1 to meet outstanding offsite mitigation requirements. Additionally, Phase 2 will allow for restoration benefits beyond the minimum area required to offset impacts from future sections of the Route 46 Corridor Improvement Project. The total area proposed for phases 1 and 2 includes approximately 4.14 acres of restoration at Centennial Creek.
Phase 1 will include grading to develop floodplain benches, widen the narrow creek channel, create secondary channels and pools, install a series of approximately 40 roughened riffles, and develop wetlands. Roughened riffles are an engineered streambed with materials that are designed to promote a pool/riffle system, prevent further head-cutting, and reverse incision. The roughened riffles will work in tandem with other improvements to the creek such as grading and vegetation planting to slow the velocity of water. These treatments will improve habitat and water quality and increase flood capacity.
Two locations with undersized culverts and associated hardscaping, rock, and/or rubble concrete will be removed and/or replaced with appropriately sized culverts. One culvert location and associated hardscaping will be removed without replacement and the streambed and banks will be restored. This culvert infrastructure is now defunct as erosion has caused the creek to flow around the culvert. One existing double culvert will be replaced with an embedded concrete box culvert.
Example of Engineered Roughened Riffle
Phase 2 will include the removal of approximately 0.32 acre of existing concrete rubble and debris and replaced with engineered streambed material.
Future Phase 2 Location at Centennial Creek
Grading, infrastructure improvement, and creation of the riffle/pool system with floodplain benches in Phase 1 will be followed by an extensive planting plan over two acres with a variety of native species to create vegetation structure and increase plant diversity and habitat quality throughout the project area. A plant establishment period will be for 3 years, followed by a monitoring period of 7 years, for a total of 10 years to ensure agency success criteria for this mitigation are met.
Project design, implementation, maintenance, and monitoring will be the responsibility of the Upper Salinas-Las Tablas Resource Conservation District through funding provided from Caltrans. The property will remain under the ownership of the City of Paso Robles as a designated Open Space element, with the site protected by a conservation easement.
Purpose and Need
The purpose of this project is to restore stream functions and values at Centennial Creek by creating, enhancing, and reestablishing wetlands and other waters to satisfy state and federal mitigation requirements.
Centennial Creek is a stream system within the same watershed as the impacts from the Route 46 Corridor Improvement Project. The system is currently in a degraded condition and would greatly benefit from restoration. This project is needed to comply with state and federal mitigation requirements that resulted from permits for the Route 46 Corridor Improvement Project. Onsite mitigation is maximized within the Highway 46 right-of-way; however additional offsite acreage is required by jurisdictional agencies that cannot be accommodated onsite. All required mitigation for the Union, Whitley 2A, Whitley 2B, and Cholame sections can be accommodated at Centennial Creek in Phase 1. Additionally, Phase 2 will provide Caltrans an opportunity to fund future restoration to remove debris and concrete rubble to restore riparian habitat and a natural streambed.
Funding
Caltrans will provide approximately $1,075,000 in funding to the Upper Salinas-Las Tablas Resource Conservation District to fund the design and construction of the proposed project. Additionally, an endowment will be established and held by the Upper Salinas-Las Tablas Resource Conservation District in the amount of $650,000 to ensure the project site is monitored and maintained according to regulatory requirements.
Schedule
Final Environmental Document Completed:
November 2021
Design Completed:
November 2021
Construction Begins (Phase 1):
June 2022
Construction Completed (Phase 1):
January 2023
