Structure-Free Zone - SFZ

These plans provide the necessary details and definitions for design and construction of the structure-free zone for a fish passable structure.

The Structure-Free Zone (SFZ) plans may be used when designing a fish passable structure to convey stream flows underneath a roadway. The SFZ is an imaginary, rectangular prism of infinite length both upstream and downstream that is horizontally centered on the stream and which represents the minimum boundary within which no part of the fish passage structure, including footings, shall be allowed.

SFZ incorporates additional width and height beyond the minimum hydraulic opening, not hydraulic related, such as constructability, maintenance access, wildlife connectivity, or other project specific needs. The plans are to be used in conjunction with Section 2.30B of the Request for Proposal (RFP).

The photo shows the application of the SFZ on Little Minter Creek, SR 302 MP 11.44.

The photo shows the application of the SFZ on Little Minter Creek, SR 302 MP 11.44.


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Slow down – lives are on the line.

In 2022, speeding continued to be a top reason for work zone crashes.

Even one life lost is too many.

Each year about 670 people are killed nationally in highway work zones. In 2022, Washington had six fatal work zone crashes on state roads.

It's in EVERYONE’S best interest.

95% of people hurt in work zones are drivers, their passengers or passing pedestrians, not just our road crews.