Fish Passage Solutions
Stream Passage Solution Priorities
When evaluating a potential road/stream crossing design and solution that prioritizes fish passage for habitat enhancement and improved migration for aquatic and terrestrial species, the following alternatives and types of structures should be considered. The priority order of solutions considered results in the maximum benefits to terrestrial and aquatic species, and the minimum long-term costs to the agency. Enhancing wildlife connectivity for all species helps native fish and wildlife more resilient to the effects of climate change stressors, such as increased stream temperatures, drought, and wildfire.
When it is not possible to decommission roads, and/or remove road crossing structures, the following solutions should be considered, in the order listed.
OPTIONS IN PRIORITY ORDER
Span the historically active floodplain or channel migration zone to minimize interference between infrastructure and channel processes, and optimize both terrestrial and aquatic species passage and full ecosystem function.
Stream Simulation Design (SSD)
Construct the following using approved SSD methodologies (in order of preference):
a. Bridge – Clear span
b. Bridge – With piers
i. Bottomless arch
ii. Round pipe
iii. Squash pipe
d. Modified SSD – Requires approval and waiver.
As a Last Resort: Hydraulic Design
This method is approved only when decommissioning and/or removing the road crossing structure is not feasible, or alternatives 1 and 2 (above) are unattainable. Hydraulic design styles include backwatered, embedded, and non-embedded culverts and culverts designed with a fishway or baffles.
Note: This solution needs sufficient planning/funding for annual, long-term monitoring and maintenance, for the life of the project.
Full Channel Width Fish Passage Solutions
Upstream and downstream of barrier outside of any resulting facility scour, take two measurements of established channel widths.
Upstream: 22 feet and 19 feet
Downstream: 24 feet and 23 feet
The average of the widths is 22 feet.
1.5 (22) + 5 = 38 feet
A full-span solution would be 38 feet or greater. Anything less is a partial, hydraulic solution.