Tuolumne River Report - U.S. Fish and Wildlife Service

RESTORING THE TUOLUMNE RIVER CORRIDORyet been received, but project approval andfunding availability will likely affect the timelinefor completion of these phases.For additional details, the complete projectconceptual design is available upon request.4.5.6. Tuolumne River SedimentManagement and ImplementationPlanBackgroundConstruction of La Grange Dam in 1893 (RM52.0) permanently ended coarse sediment supplyto the Tuolumne River channel downstream of LaGrange Dam. Because the few small tributariesentering the Tuolumne River downstream of LaGrange contribute virtually no coarse sediment,coarse sediment available for downstreamtransport is currently limited to sediment stored incontemporary channel, floodplain, and terracedeposits, or bank erosion of dredger tailings. Inthe absence of an upstream source, high flowevents have selectively transported medium-sizedparticles (gravels) from the bed surface, removinggravel bars and leaving behind large cobbles andboulders that armor the bed surface layer. Additionally,fine sediment (sand and silt) input andstorage into the Tuolumne River has increased inrecent years, as a result of tributary inputs and theJanuary 1997 flood.Fine sediment stored in spawning gravels reducessurvival of salmonid embryos. Chinook salmondepend on an adequate quantity of high qualitycoarse sediment deposits for spawning andrearing, and require a significant portion of thesedeposits to be of gravel and small cobble sizeclasses with relatively low proportions of finesediment. The reduced quantity and quality ofspawning habitat has reduced the productivecapacity of Tuolumne River spawning reaches,and has concentrated chinook salmon in shortreached below La Grange Dam that contain therelatively highest quality spawning gravels.Actions to reverse past trends in sediment supplyimbalances by balancing coarse sediment supplyand downstream routing and reducing finesediment input have the potential to increasesalmon production in the Tuolumne River andachieve chinook salmon production targets set forthe Tuolumne River.Project ObjectivesThis sediment management plan presents fourobjectives:• increase coarse sediment storage in the channelwith a large “transfusion” of coarse sediment toprovide alluvial deposits immediately availablefor chinook salmon spawning, and for eventualdownstream transport and redeposition;• maintain this restored coarse sediment storageby periodic augmentation of coarse sedimentsupply equal to the rate of downstream sedimenttransport;• implement remedial actions to prevent furtherextensive fine sediment input into the TuolumneRiver from Gasburg Creek (located nearthe upstream end of the spawning reaches);• implement actions to reduce fine sedimentstorage in the mainstem Tuolumne River.Project DescriptionThe purpose of this project is to develop andimplement a comprehensive sediment managementplan for the gravel-bedded reaches of theTuolumne River to restore coarse sediment supplyand reduce fine sediment input into the river.Four crucial tasks for restoring and maintaining abalanced sediment budget are identified: Task 1will develop a sediment management andimplementation plan that includes design,implementation, adaptive management, and themonitoring required for adaptive management.Task 1 also includes refinement of a chinooksalmon juvenile production model developed bythe Districts that can be used to predict thebenefits of sediment management toward salmonproduction. Task 2 will continue a program ofcoarse sediment augmentation (begun by CDFG),including refinement of proposed introductionsites, introduction volumes, and monitoringprotocols. Task 3 will initiate a program for finesediment reduction, by: (1) reducing fine sedimentsupplied to the upper river from the Gasburg Creekwatershed, (2) evaluating alternative methods forfine sediment reduction/removal in the mainstemTuolumne River, and (3) implementing fine sedimentremoval from the mainstem channel. Task 4will develop an adaptive management and monitoringprogram for quantifying coarse sedimenttransport to provide volume estimates for annualaugmentation, to maintain coarse sediment storagein the mainstem channel.CHAPTER 4165