Case Studies

South Fork Anker Creek

Concrete Fishway and Rock Grade Control

Location

Mad River Basin, Northern California. MAP

Project Type

  • Concrete Fishway
  • Metal Box Culvert
  • Rock Weir Grade Control

Pre-Project Barrier

  • Undersized 4.5 ft (1.4 m) diameter CMP
  • CMP at 4.5% slope with concrete lining
  • Excessive drop and water velocities
  • Exiting water dropped 5 ft (1.5 m) over riprap

Channel Characteristics

  • 100-year Flow: 420 cfs (11.9 cms)
  • Drainage Area: 0.92 mi2 (2.38 km2)
  • Bankfull Width: 8 - 10 ft (2.4 -3.0 m)

Ecological Value
Provide access to 4,000 ft (1,220 m) of upstream spawning and rearing habitats for coho salmon, steelhead and cutthroat trout.

Challenges

  • Overcome 9 ft (2.7 m) of vertical difference within 200 ft (61 m) of channel.
  • Placement of rock weirs at design elevation.

Project Funding

  • Humboldt County
  • California Dept. Fish and Game

Completion Date
November, 2002

Total Project Cost
Approximately $171,000

 


Project Description
The existing culvert was identified as a total barrier to all fish. It received a priority ranking of #9 in the Humboldt County Culvert Inventory and Fish Passage Evaluation. Additionally, the culvert inlet frequently plugged with wood, causing flows to overtop the roadway.

Dimensions of the new fishway and box culvert were determined using field observation of the stream channel width. The new span is several feet wider than the channel width at ordinary high water. Since passage of juvenile salmonids was required, weirs within the fishway have drops less than 0.6 ft (0.17 m), accommodating only 4 ft (2.1 m) of the overall grade change of 9 ft (2.7 m). This required adding additional rock grade control both upstream and downstream of the channel.

Fishway Dimensions

  Total Length: 70 ft (21.4 m) Drop over Weir:
 0.6 in (0.17 m)
  Total Headloss: 4 ft (2.1 m)
 Pool Spacing : 10 ft (3.0 m)
  Fishway Width: 15 ft (4.6 m) Min Pool Depth :
 2 ft (0.6 m)