Centennial Creek

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Project Description

Construction of the State Route 46 Corridor Improvement Project has impacted wetlands and other waters in the Union, Whitley 2A, Whitley 2B, and future Cholame section. Onsite mitigation is maximized within the Caltrans right-of-way; however, additional acreage is required by jurisdictional agencies but cannot be accommodated onsite. The remaining acreage of offsite mitigation requirements for the Union segment consists of approximately 0.474 acre of wetlands creation and enhancement, while the Whitley 2A and Whitley 2B segments and Cholame section require approximately 3.292 acres of other waters creation, enhancement, and re-establishment.

The Centennial Creek Mitigation Project intends to improve hydrology and function of the creek by removing and/or replacing undersized culverts, removing hardscaping and debris, and engineering roughened riffles (shallow portions of the creek with large rocks placed to form natural habitat) at intervals along the system to encourage aggradation and reestablishment of a riffle/pool system.  The total area proposed for mitigation is approximately 4.14 acres, which includes 0.53 acres of wetlands creation and enhancement, as well as 3.61 acres of other waters creation, enhancement, and reestablishment.  The improvements to the infrastructure will be followed by over two acres of planting a variety of native species to create vegetation structure and increase plant diversity and habitat quality.  A plant establishment period will be for 3 years, followed by a monitoring period of 7 years, for a total of 10 years after planting to successfully meet agency success criteria. 

Caltrans established a partnership with the City of Paso Robles and the Upper Salinas-Las Tablas Resource Conservation District in 2017 to identify potential project sites to meet its mitigation requirements.  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 designated Open Space, with the mitigation site protected by a conservation easement.

Project Location Map 


Project Benefits


The purpose of this project is to restore stream function and value at Centennial Creek by creating, enhancing, and reestablishing approximately 4.14 acres of wetlands and other waters to satisfy state and federal mitigation requirements.


This project is needed to comply with state and federal mitigation requirements that resulted from permits for the Union, Whitley 2A, Whitley 2B, and Cholame phases of the Route 46 Corridor Improvement Project.  The required mitigation acreage cannot be accommodated onsite along Route 46, therefore additional offsite mitigation acreage is proposed to meet this requirement.


  • Federal Highway Administration
  • City of Paso Robles
  • Upper Salinas-Las Tablas Resource Conservation District


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. 

Proposed Project Schedule

Process Date
Final Environmental Document Completed November 2021
Design Completed November 2021
Phase 1 Construction Begins June 2022
Phase 1 Construction Completed Anticipated January 2023

Project Contact 

Lucas Marsalek, Environmental Branch Chief
Phone: (805) 458-5408
Email: Lucas.Marsalek@dot.ca.gov


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Title VI Information

The California Department of Transportation (Caltrans) assures that no person shall, on the basis of race, color, or national origin, be excluded from participation in, be denied the benefits of, or be otherwise subjected to discrimination under any program or activity receiving Federal financial assistance, as required by Title VI of the Civil Rights Act of 1964, as amended, the Civil Rights Restoration Act of 1987, and Federal Executive Order 12898 (Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations).

Caltrans will make every effort to ensure nondiscrimination in all of its programs and activities, whether they are federally funded or not, and that services and benefits are fairly distributed to all people, regardless of race, color, or national origin. In addition, Caltrans will facilitate meaningful participation in the transportation planning process in a nondiscriminatory manner.