Some road-stream crossings create barriers to fish and other organism passage. Such barriers eliminate access to large areas of habitat and can have a major detrimental effect on aquatic organism populations, especially salmonids. These barriers can be classified as complete barriers that do not pass fish through in all conditions or incomplete barriers that only block passage under some conditions such as heavy rainfall.
A common example of a fish passage barrier is an undersized culvert. This can cause higher velocity than fish can pass through and erosion at the downstream end of the culvert and a drop to the stream or plunge pool surface that fish might not be able to jump through. Undersized culverts can also create blockages of debris that turn road beds into weak dams, resulting in a blowout of the roadbed and severe habitat damage downstream. Other barriers include non-functional tidegates, dams, and damaged or poorly designed culverts.
As an example, the Salmon River basin did not have a comprehensive list of barriers, but OWEB awarded SDCWC a grant to conduct a survey and prioritization of culverts in 2009. This project produced a prioritized list of fish passage barriers to guide future restoration in the Salmon River watershed. Components of the survey included:
Culvert assessments from existing reports; incorporated them into a single GIS project and database. Additional gradient criteria was added to our GIS model of road-stream crossings to identify sites for on-the-ground assessments.
Four fishers to conduct these surveys using enhanced ODFW culvert survey forms and enter data electronically. This was incorporated to the GIS project and database. ODFW and USFS helped with crew training and quality control.
Fish passage barriers were prioritized for remediation using the BLM juvenile fish passage criteria as recommended by the Nestucca/Neskowin Watershed Council's extensive review of methods.
The SDCWC tech team finalized recommendations. A detailed report produced in DVD, electronic and hard-copy. This will be used to guide future projects.