For decades, culverts on established roads have effectively disrupted the spawning and rearing behavior of all four species of anadromous salmonids in California: Chinook salmon, (Oncorhynchus tschawytschaw), coho salmon, coastal rainbow trout (steelhead are anadromous coastal rainbow trout), and coastal cutthroat trout (O. clarki clarki). Often extremely undersized, these culverts have prevented fish passage due to excessive heights between culvert outlets and plunge pools below, and impassably high flow velocities within the culverts themselves.

In 1998, 5C began to inventory migration barriers on County roads within each of the Five Counties. The inventory was completed by consulting biologist Ross Taylor and Associates, who identified a total of 245 migration barriers on county roads.

As barriers were identified in each county, they were ranked in an order from high to low priority, using site-specific information weighted heavily towards the biological considerations of anadromous salmonids. Each barrier was assigned a score based on the following five parameters:

1) Anadromous species diversity within the stream reach at     each crossing location
2) The extent of the barrier, or percent passable, generated with FishXing software
3) Habitat quality and quantity
4) Risk of culvert failure as related to sizing and flow capacity
5) Current condition of the crossing

As each crossing was assigned an individual score, they were then entered into a Prioritized Ranking Matrix, providing us with a first-cut evaluation of high priority barriers at stream crossings. Basing conservation activities on watershed, rather than political boundaries, the master ranking matrix includes the barriers identified in all five counties. That list is also broken down by county for ease of implementation.

The ranking matrix is not intended to be absolute in deciding the exact prioritization or order of projects implemented. On a site-specific basis, many factors have been and will continue to influence the selection of projects. These factors include fish observations at crossings, amount of road fill that may potentially deliver to a stream should the culvert fail, the presence of other stream crossings and barriers, project cost, schedule of other road maintenance and repair projects, and other factors impacting salmon and steelhead or project implementation. Based on this criteria, the Five Counties Program has completed 50 migration barrier removal/fish passage improvement projects, restoring access to over 124 miles of salmonid habitat from 1998-2007.