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

TUOLUMNE RIVER TECHNICAL ADVISORY COMMITTEEHABITAT RESTORATION PLAN FOR THE LOWER TUOLUMNE RIVER CORRIDORATTRIBUTE No. 4. Periodic channelbed scour andfill.Alternate bars are scoured deeper than theircoarse surface layers by floods exceeding 3- to 5-year annual maximum flood recurrences. Thisscour is typically accompanied by re-deposition,such that net change in channelbedtopography following a scouring flood usuallyis minimal. In gravel-bedded reaches, scour wasmost likely common in reaches where high flowswere confined by valley walls;ATTRIBUTE No. 5. Balanced fine and coarsesediment budgets.River reaches export fine and coarse sediment atrates approximately equal to sediment inputs.The amount and mode of sediment storagewithin a given river reach fluctuates, butsustains channel morphology in dynamic quasiequilibriumwhen averaged over many years. Abalanced coarse sediment budget impliesbedload continuity: most particle sizes of thechannelbed must be transported through theriver reach;Table 2-6. Land uses and effects on the lower Tuolumne River from 1848 to present.CHAPTER 2Land Use Time Period Location Disturbance Effect on channelPlacerMiningUrbanGrowth1848-1880 La Grange andUpstream (RM50)1850-presentModesto toWaterford (RM15 to 30)Turned over floodplainsand terraces; spoilplacement on fertileareasNeed for commerciallumber, space andaesthetic valueDestroyed natural channel morphology,increased sediment supply,destroyed instream habitat, removedriparian forestsConfined river corridor (reducedwidth), constructed dikes, removedriparian vegetation, increasedpollution loading into riverDredgerMining1880-1952 Roberts Ferryto La Grange(RM 38 to 50)Turned over entireriparian corridor valleywallto valley-wall; spoilplacement on fertileareasDestroyed natural channel morphology,increased sediment supply,destroyed instream habitat, removedriparian habitatGrazing 1850-present San Joaquinconfluence toLa Grange (RM0 to 50)Farming 1860-present San Joaquinconfluence toLa Grange (RM0 to 50)Young riparianvegetation is grazed,water sources becomefeces conduitsMature and establishingriparian vegetationis cleared. Channellocation stabilizedDestabilized banks, discouragednatural riparian regenerationConfined river corridor (reducedwidth), constructed dikes, removedriparian vegetation, increased pollutionand fine sediment loading into riverFlowRegulation1890-presentDownstream ofLa Grange (RM0 to 52)Magnitude, duration,frequency, and timing ofhigh flow regime isaltered and reduced,reduced/eliminatedsediment supply fromupstream watershedBed coarsening and downcutting,fine sediments accumulated inchannel, channel fossilized byencroaching riparian vegetation,channel migration and bar buildingvirtually eliminated, floodplainconstruction and deposition reduced,quantity and quality of instream andriparian habitat greatly reducedAggregateMining1930-presentHughson to LaGrange (RM 24to 50)Large instream and offchannel pits, dredgertailing removalHistoric floodplains are left as deepponds, floodway narrowed by dikesseparating ponds from river, riparianvegetation is cleared, regeneration isprevented and mature standseliminated.40