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

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TUOLUMNE RIVER TECHNICAL ADVISORY COMMITTEEHABITAT RESTORATION PLAN FOR THE LOWER TUOLUMNE RIVER CORRIDORCHAPTER 2vegetation. In many locations, plants initiated butwere later unable to survive because of insufficientsoil moisture. Desiccation mortality may preventinitiation for many successive years, causingdistinct age classes between successful riparianstand cohorts.Fluvial geomorphic processesChannel migration and avulsion are typicallyconsidered undesirable because migration oftenresults in damage or loss to human structures.However, channel migration (Attribute #6) was acritical process for riparian regeneration and largewoody debris introduction into the channel.Alluvial channels typically migrate across theriver valley by eroding the outside of the meanderbend and undercutting mature riparian forests.This process historically introduced woody debris,which added structural complexity to instreamhabitat (Figure 2-26). Additionally, bank erosionon the outside of the bend was balanced by bardeposition and floodplain formation on the insideof the bend (Figure 2-26). Fine sedimentsdeposited on the inside of the bend are ideal seedbeds, and if hydrological conditions provideadequate moisture, new initiating bands ofriparian vegetation advance along the buildingbar. This process is best illustrated historically inthe sand-bedded reaches, where scroll bars offiner sediments caused banding of emergentriparian vegetation on the inside of meanderbends (Figure 2-17). In the gravel-beddedreaches, substrates were coarser and drainedbetter. Consequently, riparian forests werehistorically much more extensive in the lowerriver.In sand-bedded reaches, large floods typicallyspread out over the valley and did not causelarge-scale and rapid change in channel location;rather, meander evolution and eventualcutoff were the primary avulsion processes.These meander-bend cutoffs usually left eithersloughs or oxbow lakes, and because theyinitially provided clean seed bed surfaces andconstantly moist condition, riparian regeneration(Figure 2-27) quickly occured there.An example of the dynamics of natural rivers is depicted above. (A) A channel with adequate space to migrate(Attribute 6) erodes the channel bank on the outside of the meander bend during high flows (Attribute 2), (B)encouraging aged riparian trees to topple into the channel (Attribute 9). (C) A deep pool also forms here, whichprovides structural complexity (Attribute 1) for good fish habitat. As bank erosion continues, the pool “migrates”downstream (Attribute 6), but high quality habitat is maintained. (D) On the opposite bank, high flows(Attribute 2) scour and redeposit coarse sediments (Attributes 4 and 5), forming a shallow bar on the inside ofthe meander bend (Attribute 1), and providing clean spawning gravels. (E) This area, in turn, provides idealslow-water rearing conditions for juvenile chinook salmon, as well as habitat for aquatic insects (fish food),amphibians and reptiles. (F) Progressively higher up the gravel bar surface, a dynamic interplay occurs betweenreceding water levels during the spring snowmelt (Attribute 2), and the presence of riparian tree seeds(Attribute 7). These woody riparian trees are sporadically scoured out (Attribute 8), and those established highenough on the bank are toppled into the channel as the channel migrates back across the valley (A).Figure 2-26. Conceptual role of channel migration in creating spatially and temporally complex riparian corridorhabitat.48
49Ft.Figure 2-27. 1937 photo at the confluence of the San Joaquin River, showing oxbows and scroll-bars, bank erosion, and the range of riparian ageclasses. Undisturbed floodplains and low terraces supported lush riparian forests. Note conversion of riparian vegetation to agricultural use iswell underway.CHAPTER 2LINKING PHYSICAL PROCESSES AND SALMON LIFE HISTORY
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Habitat Restoration Plan for theLow
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TUOLUMNE RIVER TECHNICAL ADVISORY C
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CHAPTER 3100Elevation (ft)110105100
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CHAPTER 3104Elevation (ft)195190185
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CHAPTER 3108Table 3-8. Wy 1970-1997
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134Relative elevation (ft)140130120
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CHAPTER 3136Relative elevation (ft)
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ADAPTIVE MANAGEMENT5. ADAPTIVE MANA
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ADAPTIVE MANAGEMENTmonitoring progr
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ADAPTIVE MANAGEMENTWILDLIFE POPULAT
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ADAPTIVE MANAGEMENT• Distribution
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REFERENCESREFERENCESAlderdice, D. F
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REFERENCESKjelson, M. A., P. F. Raq
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REFERENCESTID (Turlock Irrigation D
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APPENDIX AAPPENDIX AANNUAL HYDROGRA
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APPENDIX BAPPENDIX BTUOLUMNE RIVER
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VEGETATION SERIESNATURAL DIVERSITY
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VEGETATION SERIESNATURAL DIVERSITY
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Nature Conservancy Heritage Program
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215Scientific Name Common Name Loca
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APPENDIX BAPPENDIX B217
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