PERFORMANCE OF GRAVEL AUGMENTATION ON THE LOWER AMERICAN RIVER, LOWER SAILOR BAR 2012

The decline of salmon spawning on the Lower American River is connected to streambed degradation. Segments of river where no spawning occurs is the result of low permeability, armored streambed, and excess large gravel (Horner, 2005). This study looks at the performance of the newest spawning gravel restoration project on the Lower American River by comparing physical conditions before and after augmentation. The ability of salmonid species to successfully spawn is dependent on the physical environment; water depth and velocity, gravel size distribution, and dissolved oxygen (D.O.) each play a role in the spawning process. Experiments were conducted to characterize a salmon spawning habitat before and after restoration. Surface water depth and velocity were measured using USGS stream gauging procedures (USGS, 1980). Pre-restoration depth and velocity were nearly immeasurable because water depth across the site was too deep for accurate measurements. Post-restoration data showed water depths from 0.6 ft. to 3 ft., and velocity values from 0.7 ft./sec. to 6.4 ft./sec., both well within optimal conditions. Wolman pebble counts and bulk samples were used to characterize gravel before and after augmentation. Preliminary estimates project a decrease in median grain size and qualitative field observations confirm less streambed armoring post-restoration. D.O. was measured by inserting a mini-piezometer approximately 1 ft. into the streambed, where salmonids construct redds, and pumping water from the gravel into a flow-through cell to avoid sample contamination. Due to severe streambed armoring only two successful D.O. measurements were taken pre-augmentation. Results showed the average D.O. level before restoration to be 38%, well below optimal conditions. After gravel augmentation, 13 D.O. measurements were taken across the site and showed a low degree of variability with a high average D.O. content of 93.7%. Analysis of the site is still underway. Preliminary data shows a 250% increase in usage of the site by salmon after gravel augmentation. High resolution aerial images pre-restoration show 52 redds. Images taken post-restoration show 133 redds. It is anticipated that further study will support the finding that gravel augmentation is conducive to the success of salmon spawning on the river.