Fish Passage Case Studies

Little White Bird Creek
Stream Simulation Arch Culvert

Case Study Contributor

  • Mark Johnson, Engineer Nez Perce Tribe, Lapwai, Idaho USA
  • Nick Gerhardt, Nez Perce National Forest, Grangeville, Idaho

Location
Tributary to White Bird Creek
Salmon River Watershed, Idaho, USA MAP

Project Type

  • Open bottom steel arch culvert with concrete stem walls and footings
  • Stream simulation channel inside culvert

Pre-Project Conditions and Barriers

  • Circular CMP 60 in (1.5 m) diameter, 80 ft (24 m) long at 6.2% slope with perched outlet
  • Inadequate culvert width constricted flow at inlet
  • Perched outlet and excessive velocity due to culvert slope created migration barrier for adult and juvenile cutthroat and steelhead trout

Watershed and Channel Characteristics

  • Drainage Area: 2.31 mi2 (5.9 km2)
  • 100-year Peak design flow:
    98.6 cfs (2.8 cms)
  • Fish passage design flow:
    (2-year flow): 28.0 cfs (0.8 cms)
  • Bankfull Width: 12 ft (3.6 m)
  • Channel slope upstream: 1 to 2%
  • Channel slope downstream: 4 to 6%
  • Rosgen stream type: B3 (riffle-pool)

Ecological Value

  • 3.8 mi (6.1 km) of spawning and rearing habitat for native trout
  • Passage of all aquatic organisms and some terrestrial species, providing them with passage to avoid traversing over the 20 ft (6 m) tall road fill

Project Characteristics

  • Open bottom steel multiplate arch culvert on concrete stem wall footings,
  • 14 ft (4.2 m) span, 7.25 ft (2.2 m) rise, 92 ft (28 m) length
  • Streambed and footing slope: 3.29%
  • Culvert width equal to bankfull width plus 2 ft (0.6 m)
  • Streambed constructed inside culvert included active channel bed and banks to provide slower shallower flow along margins and terrestrial pathways

Challenges

  • Culvert located at natural break in the stream profile. Channel slope upstream is less than 2% and downstream ranges between 4% and 6%
  • Unsuitable wet material at footing level necessitated over excavating and backfilling with select fill material before forming footings.

Project Contributors

  • Nez Perce Tribe, Lapwai, Idaho
  • Nez Perce National Forest, Grangeville, Idaho

Project Funding

  • Bonneville Power Administration
  • Pacific Coastal Salmon Recovery Fund
  • US Forest Service

Completion Date
August 2006

Project Cost (2006)

Construction $ 131,774
Engineering & Design $ 12,000
Total $ 143,774


Project Summary

The Nez Perce Tribe and the Nez Perce National Forest have been working together on aquatic restoration since 2003. Restoration effort includes road decommissioning, soil restoration, and construction of this and other stream simulation culverts, such as Storm Creek. The new stream simulation culverts are designed to span beyond the bankfull width of the channel, to match the natural slope, and to have a natural substrate bottom, thus, simulating geomorphic and hydraulic conditions found in the adjacent stream channel. In addition, they are designed to pass the 100-year flood and associated sediment and debris without overtopping the culvert inlet.

The barrier culvert on Little White Bird Creek was removed and replaced with a 14 ft (4.2 m) span, 7.25 ft (2.2 m) rise, by 92 ft (28 m) long bottomless steel arch culvert on cast-in-place concrete stem wall footings. A natural stream channel was constructed through the new crossing using native streambed material collected from the crossing site and during reshaping of the upstream channel. The channel shape inside the culvert includes a well defined active channel between streambanks. Large boulders staggered in the substrate are designed to aid as resting places and to add some meander inside of the culvert. Fine material was included in the streambed mixture to fill voids and maintain surface flow.

The finished fill height over the structure was approximately 24 feet. The finished fillslopes were seeded and covered with erosion blankets. Post construction planting included native grass seed mix and native shrubs and trees on the new cut slopes which have helped control erosion and will provide shade and slope stability.

This new crossing allows fish species, such as steelhead and cutthroat trout, to access upstream spawning and rearing habitat that was previously inaccessible to them due to the configuration of the previous culvert. The larger culvert will also allow the crossing to pass flood flows and large debris with a low risk of failure. The increased capacity also stopped frequent backwatering and upstream deposition associated with the replaced culvert.

Post Project Observations and Lessons Learned

Cost overruns were incurred when unsuitable wet material was found at the footing level. This necessitated over excavating and backfilling with select fill material before placing footings. A geotechnical investigation that included borings may have alerted designers to the subsurface conditions.

The first spring following construction was drier than average and only minor channel adjustments occurred. Post construction monitoring has identified minor head cutting and channel adjustment immediately upstream of the new culvert. The numerous downed logs in the existing channel prevented head cutting from proceeding further upstream. Several boulders placed in the culvert have created small pools and provide resting areas for migrating species. Some aggradation has been observed at the outlet of the new culvert as material from the culvert and upstream channel moved downstream. The designers anticipate that the large rocks placed in the culvert will cause some realignment and promote some limited sinuosity in the channel in the culvert.

Published 05/27/08