Introduction 1 Purpose and scope 1 Approach 3 Sediment-budget concept 3 Application of sediment-budget concepts to Lake Tahoe tributaries Description of the study areas 4 Lake Tahoe basin 4 Study basins 5 Blackwood Creek 5 General Creek 7 Edgewood Creek 10 Logan House Creek 10 Streamflow conditions during study 12 Development of the suspended-sediment budgets 12 Gross and routed suspended-sediment budgets 14 Hillslopes 14 Erosion boxes 14 Gullies 15 Channels 15 Channel cross-sectional surveys 15 Channel inventories 16 Bank and bed sampling 17 Assumptions and sources of errors 17 Application of methods to study basins 18 Blackwood Creek 18 Hillslopes 18 Tributaries 20 Main channel 23 General Creek 23 Edgewood Creek 24 Hillslopes 24 Channels 24 Logan House Creek 26 Suspended-sediment budgets 27 Blackwood Creek 27 General Creek 27 Edgewood Creek 29 Logan House Creek 29 Basin and channel characteristics affecting suspended-sediment budgets 30 Hillslope erosion 30 Geologic effects 30 Effects of rodent activity 31 Channel erosion 32 Effects of channel characteristics 32 Effects of Streamflow 34 Geologic effects 35 Contents III Basin and channel characteristics affecting suspended-sediment budgets-Continued Land-use considerations 35 Increased runoff 35 Sediment supply 36 Gully formation 36 Relevance of study results to long-term sediment loads 36 Conclusions 37 References cited 38 FIGURES 1-5. Maps showing: 1. Location of study basins tributary to Lake Tahoe 2 2. Location of composite reaches, tributary reaches, cross sections, hillslope-erosion sites, and gaging station, Blackwood Creek basin 6 3. Location of composite reaches, cross sections, and gaging station, General Creek basin 9 4. Location of composite reaches, cross sections, hillslope-erosion sites, and gaging station, Edgewood Creek basin 11 5. Location of composite reaches, cross sections, and gaging station, Logan House Creek basin 12 6. Photograph showing uncovered erosion box 15 7. Schematic representation of suspended-sediment budget for the Blackwood Creek basin 20 8,9. Graphs showing: 8. Percentage of sediment mobilized by hillslope, streambank, and streambed erosion 33 9. Total sediment finer than 2 millimeters, normalized by drainage area, mobilized by all processes and by streambank erosion 34 10. Photograph showing dense riparian vegetation along the stream channel of Edgewood Creek 35 11. Graph showing volume of stored sediment, by category, along main channels in the study basins 37 TABLES IV Contents Conversion Factors, Vertical Datum, and Definition Conversion Factors Multiply By To Obtain cubic meter (m3) 35.31 *j Vertical Datum Temp °F = 1.8 temp °C + 32. Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929-a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.
