Sediment transport in two tributaries to the San Joaquin River immediately below Friant Dam—Cottonwood Creek and Little Dry Creek, California

First posted May 2, 2023 For additional information, contact: Director,California Water Science CenterU.S. Geological Survey6000 J Street, Placer HallSacramento, California 95819 Two tributaries to the greater San Joaquin River watershed, Cottonwood and Little Dry Creeks, in California’s Central Valley, were assessed for sediment streamflow dynamics between October 1, 2011, September 30, 2019. The two systems deliver below Friant Dam, California. Dams create downstream discontinuities transport therefore influence fish habitat dynamics. Because these creeks are directly downriver from they become most upstream source of Dam.The quality quantity spawning gravel-bedded reach relies on a range bed material particle size suitable redd structure. effects coarse-sand fine-gravel supply salmonid depends primarily timing its addition River; thus, understanding timing, quantity, supplied is critical management ecological biological sustainability.Streamflow along with compared continuously measured water-surface elevations quantify direction streamflow. Suspended-sediment samples collected multiple automatic samplers analyzed concentration grain-size distribution. Measured suspended-sediment concentrations streamflows used develop rating curves compute continuous estimates load each tributary. Satellite imagery was qualify spatial temporal through lower watersheds support more quantitative sediment-load estimates.Computed annual loads ranged 1.32x101 2.68x104 metric tons Creek 9.82 1.98x103 Creek. Sediment computed during study period both show that highest water year 2017 (October 2016, 2017). occurred months January March. In tributaries, distributions suspended predominantly coarse-sized sand finer than remnant material.Both demonstrate backwater River, but tortuous stream channel historical mining pits within provide capacity storage less complex network based streamgages not at confluence tributary do represent direct flux into instead, results indicated Creek, particularly, lowest portion watershed stores before it reaches River.