Mickelson, E., Smith, D. and Hinton, S., 2020. Skagit Basin Barrier Culvert Analysis – Public and Private Stream Crossings. Skagit River System Cooperative, La Conner, WA. pp. 72.

Barriers that prevent access to existing aquatic habitat have been identified as one of the most
significant limitations to salmonid productivity in the Pacific Northwest (Shear and Steel 2006).
Transportation corridors, agriculture, urbanization and other human land-use practices have diminished
the availability of spawning and rearing habitats for all cold-water dependent species native to the
region (Montgomery 2005, Bilby and Mollot 2007, Hall et al. 2018). A major feature of these land uses is
the presence of culverts and other structures that facilitate road crossings of streams and wetlands.
While these structures are often adequate to allow water to move through the road crossing, they can
impede the passage of anadromous and resident salmonids by creating conditions that exceed the
swimming abilities of adult or juvenile fish.
In the Skagit River Basin, efforts have been made by various organizations over the years to inventory
and assess crossings for barrier status, but available datasets are aging, which has made restoration
planning difficult. This project represents an attempt to address these problems by consolidating and
updating available data while documenting new barriers and the habitat they isolate. Due to their
prevalence, we have chosen to begin this work by focusing on culvert crossings, reserving other barrier
structures for future efforts. We have worked to create a current database that captures the known
universe of culvert barriers on as many public and private road crossings as possible within the Skagit
River basin. Our hope is that the database and the analyses presented here will support informed
allocation of limited resources towards efforts to restore habitat access for anadromous salmonids.
This document begins with an overview of our process and rationale for narrowing the geographic scope
that we used to derive our list of barrier culverts. This is followed by a description of our process for
reconciling and updating available data, along with methods for barrier and habitat assessment. While
we leave the task of prioritizing individual culvert projects to the governments, agencies, landowners,
and organizations considering undertaking barrier correction efforts, we have broken out our summary
of results in ways that we feel will be useful for assisting such decisions (Appendix A). We also present,
in the form of two appendices, subsets of our full culvert database that are limited to areas relevant to
Salmon Recovery Funding Board (Appendix B) and Puget Sound Energy (Appendix C) funding sources.
BACKGROUND
Culvert crossings, by a large margin, make up the greatest proportion of artificial (human-made) fish
passage barriers in Washington State (WDFW 2019). Small dams, diversions, and similar structures,
while not as widespread as culverts, also have similar negative impacts. Many of these barriers
completely block passage for all fish at a wide range of flows, while some are partial barriers that block
passage only for certain species or life stages, or during certain flow conditions.
There have been numerous efforts to inventory fish passage barriers throughout the Skagit River basin
over many years, with the most comprehensive effort taking place from 1995 through 2001 as a
combined effort between the Washington Department of Fish and Wildlife (WDFW) and the Skagit
System Cooperative (SSC). The effort stemmed from work to complete an off-channel habitat inventory,
during the course of which it become apparent that many barriers had not been mapped or assessed.
The unique-for-the-time State/Tribal collaborative effort resulted in the first relatively comprehensive