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

LINKING PHYSICAL PROCESSES AND SALMON LIFE HISTORY2.2.3. Channel morphology (crosssection and planform)Prior to flow and sediment regulation, the TuolumneRiver downstream of La Grange behavedalluvially; the channelbed and banks were composedof alluvium (gravel, cobble, boulders), andthe flow regime and sediment supply were adequateto form and maintain the bed and bankmorphology. Variability in hydrologic and geologicalcontrols (e.g., valley width, location andelevation of underlying bedrock) created variableand complex local channel morphologies. Asdescribed in the hydrology section, streamflowswithin a given year and between years varied fromas low as 100 cfs in summer months to peak winterfloods exceeding 100,000 cfs. The valley wallsconfined the river corridor to as narrow as 500 ftnear Waterford (RM 32.0), whereas reachesdownstream of Modesto were virtually unconfined.Bedrock grade control upstream of Modestoalso varied, with exposed bedrock formations nearthe water surface in some locations, and over 50feet below the riverbed in other locations. TheseGRAVEL-BEDDED ZONE (RM 24.0-52.1)CHAPTER 2REACH 7(RM 46.6-52.1)Dominant SpawningReach• Gravel bed andbanks• Longitudinal slopebetween .0010 and.0015• Little valleyconfinement withinbluffs• River corridorconfined byriparian encroachment• Land use predominatelyagriculture(livestock grazing)• Remnant dredgertailings fromhistoric goldmining, most ofwhich was removedfor New Don PedroProject constructionREACH 4 (RM 24.0-34.2)In-Channel Gravel MiningReach• Gravel bed and banks• Longitudinal slope between.0003 and .0015• Little valley confinementwithin bluffs• River corridor confined byagricultural encroachment• Land use predominatelyoff-channel aggregateextraction and agriculture(orchards)• Extensive history of inchannelaggregate extractionREACH 5 (RM 34.2-40.3)Gravel Mining Reach• Gravel bed and banks• Longitudinal slopebetween .0010 and .0015• Moderate to little valleyconfinement within bluffs• River corridor confinedby agricultural encroachmentand dikes separatingriver from off-channelmining pits• Land use predominatelyoff-channel aggregateextraction and agriculture(orchards and row crops)REACH 6 (RM 40.3-46.6)Dredger Tailing Reach• Gravel bed and banks• Longitudinal slopebetween .0010 and.0015• Little valley confinementwithin bluffs• River corridor confinedby riparian encroachment• Land use predominatelyagriculture (livestockgrazing)• Remnant dredgertailings from historicgold mining, some ofwhich was removed forNew Don Pedro Projectconstruction31