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OWEB has continued to see fish passage improvement rank among the most numerous restoration actions on the landscape. The main objective for fish passage improvement is to reconnect fish to stream habitat that has been made inaccessible through road building activities and other land uses. This restoration action can often provide an almost immediate benefit to fish populations by expanding spawning and rearing areas.
Effectiveness monitoring of fish passage improvement actions seeks to determine whether these investments continue to function over time and if not, the cause(s) of failure.
Using OWEB’s database, a random sample of fish passage improvement projects installed between 1997 and 2000 were selected. Contractors set out to rediscover the project sites and collect field data that would determine the likelihood of the project site to pass fish in 2009. Additionally, snorkel surveys were conducted to find out if juvenile salmonids were occupying the habitat upstream from the improvement. The study also used computer modeling software in conjunction with actual field measurements to determine the functional hydraulics of the culverts.
Executive Summary (2009)
Final Report (2009)
Juvenile salmonid use upstream from the projects:
All bridges included in the study were considered to be fish passable at all flow conditions.
Computer modeling software found that all culverts were partial barriers to juvenile fish passage at certain flow conditions even though field sampling showed only 3 culverts not having juvenile salmonids above the project. The computer simulation identified 8 culverts as 100% barriers to juvenile fish passage even though these culverts also had juvenile salmonids upstream of the culvert. These discrepancies are most likely a reflection of the conservative nature of the software and its inability to estimate results of varying types of culvert designs.
This information will help guide future fish passage improvement efforts and provides a good starting point to evaluate additional areas of the state for fish passage improvement effectiveness over time. The results of the study can aid in the development of more accurate computer modeling software that can simulate new types of culvert designs.
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