Clear Creek Gravel Injections
As part of a basin wide goal to restore sediment transport continuity for 16 miles of Clear Creek below Whiskeytown Dam, GMA developed a series of gravel augmentation strategies to complement existing gravel injections. Lateral bars and talus cones deliver gravel during high flows, but since such flows seldom occur near the dam, some injections supplement riffles, providing habitat benefit during prolonged periods of lower flows. Some sites employ a combination of injection types. Nearly 200,000 tons of gravel had been placed in Clear Creek as of 2017. These injections, coupled with dam removal and floodplain restoration efforts, have restored nearly half of the below-dam channel to a more alluvial condition which has provided thousands of square feet of spawning habitat. Further, the increase in sediment supply has increased flow heterogeneity by directing the stream into complex patterns, increased channel dynamism via flow-impingement against and consequent erosion of heavily vegetated banks, and has increased bed mobility in coarsened reaches.
The first photo above describes a lateral berm located in a bedrock constriction below a major tributary, offering superb sediment transport capacity characteristics. The injection has been recharged numerous times since 2005 with over 16,000 tons of spawning gravel. Occasional pulse flows, dam spills, and tributary generated peak flows have repeatedly mobilized the injection and recharged over 2,000 feet of spawning habitat in a bedrock gorge. Gravel is placed using methods ranging from end-dumping (talus cones) to grading (lateral berms) to sluicing (placed riffles). projects are monitored using ground and aerial photos, topographic surveys and qualitative assessments following high flows. GMA's geomorphic monitoring data is often incorporated into USFWS' spawning habitat mapping data and the results are used to inform future gravel augmentation strategies.