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

GEOMORPHIC AND RIPARIAN INVESTIGATIONSTable 3-5. Potential fine sediment point sources between RM 32 and RM 52.RM Bank Tributary Sand input potential51.3 North Mill gulch Low50.3 North Gasburg Creek Large49.7 North Morton Gulch Dissipates on floodplain/terrace48.9 North Upper Dominici Creek Dissipates on floodplain/terrace47.8 North Lower Dominici Creek Moderate47.0 North Un-named gulches at Basso Br Low45.5 North Un-named gulch Dissipates onto floodplain/terrace45.2 South Peaslee Creek Large44.7 North Rairden Gulch Dissipates onto floodplain/terrace41.0 North Salter Gulch Dissipates onto floodplain/terrace40.5 North Numerous gullies Dissipates onto floodplain/terrace40.2 North Warner Gulch Unknown, no delta observed39.5 North Roberts Ferry Nut Company gully Sediment excavated from roadside38.9 North Un-named gully Dissipates onto floodplain/terrace38.6 North Un-named gully Dissipates onto floodplain/terrace38.2 North Un-named gully Low (empties to Ketcham Slough)37.0 North Sidecast from orchard road Low (sheet erosion into river)35.5 North Un-named gully Dissipates onto floodplain/terrace35.3 North Road cut erosion Dissipates onto floodplain/terrace34 South Hickman Drain Low (long, flat backwater)CHAPTER 3primarily livestock grazing, row crops, or alfalfacultivation; however, because these areas werenearly flat (low slope), sand generation within thecorridor soils appeared to be very low.The June 8, 1993 aerial photographs capture theTuolumne River after a relatively wet water yearpreceded by five relatively dry water years. Peakdischarges at LaGrange were less than 2,000 cfsthroughout the five dry years and one wet wateryear. We hypothesize that the mainstem flowswere low enough for significant deltas wouldpersist. Therefore, any resultant tributary deltas inthe Tuolumne River visible in the June 8, 1993air photos could be used as a measure of therelative sediment loading by individual tributariesand gullies to the mainstem over five droughtyears and one wet year.Of all the tributaries upstream of Waterford (RM32.0), only three tributary deltas were conspicuousin the June 8, 1993 air photos: Gasburg Creek(RM 50.3), Lower Dominici Creek (RM 47.8),and Peaslee Creek (RM 45.2). Based on 1997field observations, we initially estimated averagetributary delta depths of 6 feet. Using thisapproximation, the approximate delta volumes forGasburg Creek was 380 yd 3 , Lower DominiciCreek was 325 yd 3 , and Peaslee Creek was 380yd 3 . By assuming a depth of 6 feet, volumeestimates are simply surrogates for surface area ofdelta material. This evaluation showed that thesethree tributaries were delivering enough finesediment to the Tuolumne River to be observed ona 1 inch = 500 ft scale aerial photograph. Noother tributaries had observable deltas.In April 1997, all tributaries and gullies within thestudy area were located and inspected to verify/refute observations from the 1993 aerial photographs,and to evaluate whether tributaries andgullies were delivering their sand load into theTuolumne River. Most gullies on the valley wallsempty onto cultivated fluvial terraces; thencultivation spreads the sediment and prevents it89