Little French Creek

Hybrid Pool and Weir Fishway

Location
Trinity River Basin, Northern California, USA. MAP

Project Type

  • Hybrid Pool and Weir Fishway with Concrete Pools and Removable Wood Baffles
  • Hydraulic Design

Pre-Project Conditions

  • 10 ft (3.0 m) span x 10 ft (3.0 m) high Concrete Arch culvert with a 15 to 20 ft (4.6 - 6.1 m) cascading outlet drop into Trinity River
  • Nonfunctional wooden and rock masonry Denil fish ladder damaged by floodwaters
  • Wooden offset baffles through culvert considered to function adequately

Pre-Project Barriers

  • Velocity barrier
  • Turbulence barrier
  • Lack of resting pools
  • Complete barrier for all smaller fish

Watershed Characteristics

   Little French Creek

  • Drainage Area: 6.4 mi2 (16.6 km2)
  • High Design Flow (100-year Flow): 2,000 cfs (56.6 cms)
  • Upstream Channel Width: 5 to 15 ft (1.5 to 4.6 m)

   Trinity River

  • Drainage Area: 1,400 mi2 (3,626 km2)
  • High Design Flow (100-year Flow): 393,000 cfs (11,130 cms) with 235 ft (71.6 m) channel width
  • Low Design Flow: 300 cfs with 110 ft (33.5 m) channel width

Ecological Value

  • Provide access to 3 miles (4.8 km) of upstream spawning and rearing habitat for coho, chinook, steelhead, and rainbow trout

Project Characteristics

  • Pool and weir fishway providing passage from Trinity River to baffled culvert on Little French Creek
  • Fishway Dimensions: 97 ft (29.6 m) long with 19.3 ft (5.9 m) total head loss
  • 20 weirs with dimensions: 2 ft (0.6 m) long x 3 ft (0.9 m) high x 1 ft (0.39 m) drop

Challenges & Lessons Learned

  • Providing fish passage over a 19 ft (5.9 m) drop in less than 90 ft (27 m) of channel
  • Building a structure to withstand Trinity River flood flows
  • Fitting aesthetically within a high recreational-use Wild & Scenic River

Project Contributors

  • California Dept. of Transportation
  • California Dept. of Fish and Game
  • National Marine Fisheries Service
  • USDA Forest Service
  • California Conservation Corps

Project Funding
California Dept. of Transportation

Completion Date
November 2001

Project Cost

Project Development $ 125,000
Construction Management $ 48,000
Environmental Permitting $ 14,000
Re-Vegetation $ 3,000
Construction (Contracted) $ 255,000
Total $ 445,000
 


Project Description

In 2001 Caltrans, in partnership with California Dept. of Fish and Game and the National Marine Fisheries Service, re-constructed a fishway on Little French Creek at the confluence with the Trinity River. The 10 ft (3.0 m) wide concrete arch culvert that passes under State Route 299 had been retrofitted in the 1970’s with removable wood baffles and a Denil fish ladder at the outlet. The wooden Denil fishway with rubble masonry pools frequently sustained damage during high flows in both the Trinity River and Little French Creek. The new fishway incorporates a compact pool and weir design, allowing tighter spacing between pools and increasing the overall slope. Additionally, a turn was placed into the fishway to obtain the needed length. The fishway was designed to be partially sunken into the bank of the Trinity River to protect it from high flows and partially hide it from view. An aesthetic treatment that resembles cobbles was added to the exposed walls to help further blend the fishway with the surrounding environment. The project also had follow-up plantings adjacent to the fishway. Removable wood baffles were used in the fishway to facilitate removal of accumulated debris. Adult salmonids were observed in the upper most pools of the fishway and upstream of the culvert post project.

Fishway, Pool, and Weir Dimensions
  Fishway Length : 97 ft (29.6 m) Pool Length :
 8 ft (2.4 m)
  Total Head Loss: 19.3 ft (5.9 m)
 No. of Weirs: 20
  Overall Slope: 20% Drop Over Weir :
 ~1 ft (0.3 m)
  Fishway Width: 9.75 ft (3.0 m) Weir Length: 2 ft (0.6 m)
  Pool Width: 3 ft (0.9 m)
 Weir Height: 3 ft (0.9 m)