Aquatic Organism Passage at Road Crossings

Fish Passage Projects for Marin County Public Works

Location: Marin County, California
Clients and Partners: Marin County Department of Public Works

Michael Love & Associates (MLA) served as the fish passage engineers for design of five fish passage restoration projects for Marin County road-stream crossings. Working with Stetson Engineers and the Marin County Department of Public Works, MLA developed solutions that met fish passage, stream protection, and transportation objectives and constraints. Projects included:

  1. Two new arch culverts with 4-percent sloped roughened channels designed to protect the stability and habitat of the upstream channel from headcutting and incision,
  2. A roughened rapid raising the channel downstream of a perched box culvert to eliminate a perched culvert outlet, and
  3. Two new stream simulation arch culverts that span the bankfull channel and have streambed morphology within the culverts that mimic the adjacent natural channel.

Design activities for the roughened channels involved determining stable rock gradations for bed and banks, designing channel bed features to simulate natural steep-channel morphology, and analyzing water velocities, depths, and turbulence for passage of adult and juvenile coho salmon and steelhead trout. The stream simulation crossings were designed with a self-sustaining stream channel within the culvert that mimics the natural channel morphology. Reference channel reaches were surveyed and geomorphically characterized for use in developing each stream simulation design.

To-date, four projects has been constructed and the fifth is scheduled for constriction in summer of 2010. Working closely with the regulatory agencies allowed for these projects to be constructed within 3-months of completing final design.