Abstract ........................................................ 1
Introduction, Purpose, and Scope ................................ 2
Sandy River Basin—Physiography, Geology, and Hydrology .......... 4
Marmot Dam Setting and Removal .................................. 9
Context ...................................................... 9
Preremoval Studies .......................................... 10
Dam Removal ................................................. 10
Reservoir Erosion .............................................. 13
Knickpoint Migration and Initial Sediment Erosion ........... 13
Longer Term Reservoir Erosion and Bed Coarsening ............ 13
Sediment Deposition ............................................ 19
Initial Sediment Deposition Following Breaching ............. 20
Longer Term Sediment Deposition near the Dam Site ........... 25
Deposition Farther Downstream ............................... 25
Deposition and Channel Geometry ............................. 29
Sediment Transport ............................................. 29
Sediment-Transport and Water-Discharge Measurements ......... 31
Suspended-Sediment Transport ................................ 31
Prebreach Transport ...................................... 32
Transport at the Time of Breaching ....................... 34
Transport by Subsequent High Flows ....................... 34
Annual Sediment Fluxes ................................... 34
Bedload Sediment Transport .................................. 37
Transport at the Time of Breaching ....................... 39
Transport by Subsequent High Flows ....................... 40
Annual Sediment Fluxes ................................... 41
Estimated Sediment Budget ...................................... 42
Discussion ..................................................... 45
Timing, Rate, and Processes of Reservoir-Sediment Erosion ... 46
Knickpoint Evolution ........................................ 47
Spatial and Temporal Trends in Sediment Transport ........... 47
Spatial and Temporal Trends in Sediment Deposition .......... 50
Observations and Measurements Compared to Prebreach
Modeling .................................................... 51
Implications for Monitoring Dam Removals .................... 53
Conclusions .................................................... 55
Acknowledgments ................................................ 56
References Cited ............................................... 56
Appendix—Methods for Assessing Sediment Erosion, Deposition,
Water Discharge, and Sediment Transport ........................ 62
Sediment Erosion and Deposition ............................. 62
Data ..................................................... 62
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