Restoring Coastal Lagoons and Wetlands on California's Scenic Highway 1

Jennifer Moonjian, California Department of Transportation
Katherine Brown, Cecilia Boudreau, Linda Baker & Mindy Trask - California Department of Transportation
Topic Area
Mitigation for Transportation Projects

In fall of 2015, the California Department of Transportation (Caltrans) began construction to realign over two miles of roadway along California's Scenic Highway 1. The purpose of the project was to realign the highway between 100 and 500 feet inland, away from coastal bluff erosion. This stretch of California's coastline is home to at least six federally protected species, an equal number of plants and wildlife considered rare or species of special concern by the state of California, and over 90 acres of wetlands; all located within the unique setting of a pristine coastal prairie grassland. Over 12 agencies from federal, state and local governments were involved in the permitting process. During design and construction, Caltrans explored ways to avoid and minimize impacts to natural resources. In addition, the Piedras Blancas Realignment project also implemented compensatory mitigation for impacts that occurred.

Development of innovative measures that would avoid and minimize impacts to wetlands, waters, and sensitive species started in the early 2000s during the environmental analysis and preliminary design phase. The highway was ultimately designed to include construction of three bridges which spanned streams and large areas of wetland. A permeable road base was designed to allow water to flow uniformly underneath the highway in wetland locations that could not be spanned by a bridge. Design exceptions were approved so that slopes could be steepened to minimize the footprint of the new roadway. Additional efforts were made during construction to protect natural resources, including building the bridges from trestles, a full-time biological monitor, collection and placement of topsoil, extensive ESA fencing, landform grading, native vegetation transplanting, and invasive plant management.

The compensatory mitigation for this project was two-fold: Restore wetlands and waters on-site along the old roadbed and create, as well as enhance wetlands at an off-site location. Upon completion of the new highway, the old roadbed was removed, recontoured, and replanted with native plants and seed using topsoil that was saved from the excavation of the new alignment. In off-site locations where soils and hydrology were not suitable for sustaining wetlands, Caltrans conducted a pilot test using a mixture of bentonite and native soils to create wetlands to help inform additional off-site mitigation planned in a fallow agricultural field just north of the project.

There is an exhaustive list of challenges on this project including those that involved elephant seals, tidewater goby, burrowing owls, local genetic native seed collection and seed increase, native plant propagation, compost, and permitting. The road construction portion of the Piedras Blancas Realignment project was completed at the beginning of 2018 and has many valuable successes and lessons learned that we can share to improve wetland and waters restoration for future projects.

Abstract Keywords
coastal wetlands
Mitigation
innovation