FSH 7709.56b - DRAINAGE STRUCTURES HANDBOOK
R-1 SUPPLEMENT 7709.56b-90-1
EFFECTIVE 01/15/91
CHAPTER 6 - HYDRAULICS
6.26 - Fish Passage. Fish passage requirements in a stream may dictate use of a culvert or bridge
larger than is hydraulically necessary and, therefore, increase the cost. The fishery biologist
should ensure no natural barriers to fish passage exist above or below the crossing site which
would negate the beneficial, effect of installing a larger structure. The fishery biologists report
should identify fish species, miles of fishery above and below the structure, period of year
passage is required, maximum and minimum flows at which fish passage is required, and culvert
velocity constraints at a minimum.
6.26a - Design Requirements for Fish Passage.
1. Fish Passage Required. Fish passage will be a design requirement on any stream,
regardless of size, whether perennial or intermittent, that is utilized by anadromous or resident
fish during any period of the year, and where passage is necessary to ensure use of available
habitat. In addition, fish passage should be considered for the following types of streams:
a. Any stream that has a history of fish production but whose production has been
eliminated because of a barrier that can reasonably be expected to be removed.
b. Any stream that has significant potential for fish production but has had its production
precluded by some condition that can be resolved.
Upstream movement of adult fish should not be prevented by the structure more than 10 percent
of the time when fish are migrating; however, the structure does not have to be designed to
permit fish migration during flood flows. Fish passage design requirements (maximum
velocities and distances, etc.) and minimum depth of flow should be provided to the design
engineer by the hydrologist as recommended by the fishery biologist. There is a 10 percent
chance that a 10-year storm will occur in any one year. Therefore, the fish passage requirement
for either spring or fall spawners should be designed for Q10. Minimum water depth should be
computed from the annual low flow probable during spawning season.
Where fish passage is to be provided the following criteria shall apply:
(1)
Maximum water velocities (Q10)
Velocities for the design flow (Q10) in the natural stream will not be exceeded through the
structure.
(2)
Minimum water depth (Q1)
12 inches for salmon, steelhead, sea-run, cutthroat, and other trout over 20 inches; 6 inches for
trout under 20 inches and kokanee.
FSH 7709.56b - DRAINAGE STRUCTURES HANDBOOK
R-1 SUPPLEMENT 7709.56b-90-1
EFFECTIVE 01/15/91
(3)
Maximum jump (vertical height)
Salmon and steelhead
Trout and kokanee
Single Jump
3 feet
1 foot
Multiple Jump
1 foot
0.5 feet
Where more than one species is present, criteria should be selected that will accommodate all
species.
If fish passage is required, the culvert can be designed to act as a bridge; that is, the natural
streambed is carried through the structure on the same grade. The structure is designed to pass
the 50-year event, but velocities for fish passage will be computed from the 10-year event. Low
flow depth should be calculated from the annual low flow probable during spawning season and
a low flow channel placed in the invert if needed.
If a low water crossing or overflow channel is designed for a location where fish passage is
required, the water opening under the roadway will be designed to pass the 10-year event under
the above velocity constraints for fish passage. The structure itself will be designed to pass the
50-year event and should not cause environmental damage in the 100-year flood plain.
Figure 2 shows spawning periods for various species of fish. Low water flow for fall spawners
and high spring runoff flows for spring spawners should be analyzed for velocity and "jump" to
assure passage where spawning waters have been identified.
Structures recommended for fish passage (unless a fish ladder or baffle system is added to an
existing site) are:
Bottomless arch
Pipe-arch with buried invert
Circular pipe with buried invert
Bridges
Reference to FSM 2505 (R-1 Supplement) for general ecological and environmental
considerations.
2. Fish Passage Not Required. If fish passage is not a requirement, culvert design is
simplified by hydraulic charts for standard sized and types. The culvert should convey the 50year design storm and should not cause environmental damage in the 100 year flood plain.
Where water quality constraints require it, fords or similar structures shall be designed so the
water opening under the roadway will pass the annual event. In all cases, the structure will be
designed to pass the 50-year event without causing environmental damage in the 100-year flood
plain.
FSH 7709.56b - DRAINAGE STRUCTURES HANDBOOK
R-1 SUPPLEMENT 7709.56b-90-1
EFFECTIVE 01/15/91
6.26b - Types of Culvert Installations.
1. Design Procedures. General. There are several good references available for the
hydraulic design of culverts. Recommended is "Hydraulic Design of Highway Culverts",
Federal Highway Administration, Report No. FHWA-IP-85-15, September 1985. also
recommended are "Hydraulic Design of Energy Dissipators for Culverts and Channels", Circular
No. 14, Department of Transportation 1974, and "Use of riprap for Bank Protection", circular
No. 11, Department of Transportation 1967.
2. Fish Passage Structures. If flow requirements dictate a rock invert be used to reduce
velocities, Manning's formula is used for pipe sizing. The "n" value will be for the rock size or
riprap used in the invert, and the "n" of the pipe sides averaged for a composite "n." If possible,
the fishery biologist should aid in final riprap placement to enhance the fishery.
Although many good reference texts are available, the following is recommended as the most
recent and comprehensive: "Fish Migration and Fish Passage," by Willis Evans and Beryl
Johnston, USDA, FS, WO, E-7100-12, June 1980.
Figure 2 - Spawning Chart view in hard copy.