Magnitude and Frequency Data for Historic Debris Flows in Grand Canyon National Park and Vicinity, Arizona By THEODORE S. MELIS, ROBERT H. WEBB, PETER G. GRIFFITHS, and THOMAS W. WISE U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 94 4214 Prepared in cooperation with the BUREAU OF RECLAMATION Tucson, Arizona 1995 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not constitute endorsement by the U.S. Government. For additional information Copies of this report can be write to: purchased from: Regional Research Hydrologist U.S. Geological Survey U.S. Geological Survey, MS 472 Open-File Section Water Resources Division Box 25286, MS 517 345 Middlefield Road Denver Federal Center Menlo Park, CA 94025 Denver, CO 80225 CONTENTS Page Abstract...................................................................................................................................................... 1 Introduction...........................................................................^ 2 Purpose and scope.............................................................................................................................. 3 Units and place names........................................................................................................................ 3 Acknowledgments.............................................................................................................................. 6 Debris flows in Grand Canyon National Park............................................................................................. 6 Debris-flow transport of sediment to the Colorado River.................................................................. 7 Effects of debris flows on rapids........................................................................................................ 10 Effects of debris flows on sand bars................................................................................................... 12 Methods of study......................................................................................................................................... 15 Delineation of geomorphically significant tributaries........................................................................ 15 Selection criteria for tributaries.................................................................................................... 15 Areas not assigned to tributaries................................................................................................... 15 Estimation of drainage areas......................................................................................................... 15 Delineation of eleven study reaches of the Colorado River......................................................... 15 Determination of frequency for debris flows..................................................................................... 16 Repeat photography...................................................................................................................... 16 Radiometric dating techniques..................................................................................................... 16 Measurement of sediment characteristics........................................................................................... 17 Point counts.................................................................................................................................. 17 Sources of particles >2 mm.......................................................................................................... 20 Largest boulders............................................................................................................................ 20 Dry-sieve analysis......................................................................................................................... 20 Clay mineralogy............................................................................................................................ 22 Reconstitution of water content.......................................................................................................... 23 Peak-discharge estimates................................................................................................................... 23 Streamflow .................................................................................................................................. 23 Evidence of debris-flow process and peak-discharge stage......................................................... 23 Sediment-yield estimates.............................................................................................................. 24 Indirect estimates of debris-flow peak discharge ........................................................................ 24 Superelevation and runup estimates............................................................................................. 25 Geomorphically-significant tributaries of the Colorado River................................................................... 28 Source areas and initiation mechanisms for debris flows in Grand Canyon............................................... 29 Documentation of historic debris flows...................................................................................................... 31 Magnitude and frequency data for specific tributaries................................................................................ 31 Cathedral Wash (river mile 2.8-R)..................................................................................................... 31 Badger Canyon (river mile 7.9-R)...................................................................................................... 32 Soap Creek (river mile 11.2-R).......................................................................................................... 32 House Rock Wash (river mile 16.8-R)............................................................................................... 36 "18-Mile Wash" (river mile 18.0-L).................................................................................................. 36 Discharge estimate........................................................................................................................ 39 Sediment characteristics............................................................................................................... 43 Effects on the separation bar......................................................................................................... 44 Frequency .................................................................................................................................. 45 Unnamed tributary at river mile 19.9-L............................................................................................. 45 Unnamed tributary at river mile 30.5-R............................................................................................. 48 Nautiloid Canyon (river mile 34.7-L)................................................................................................ 48 Unnamed tributary at river mile 42.9-L............................................................................................. 48 Tatahoysa Wash (river mile 43.2-L).................................................................................................. 52 Unnamed tributary at river mile 62.5-R............................................................................................. 53 Contents i CONTENTS Continued Page Sediment yield estimate................................................................................................................ 53 Sediment characteristics .............................................................................>................................. 53 Boulder transport.......................................................................................................................... 53 Effects on the Colorado River...................................................................................................... 56 Frequency .................................................................................................................................. 56 "Crash Canyon" (river mile 62.6-R).................................................................................................. 56 Source area sediments................................................................................................................... 56 Discharge estimates and sediment characteristics........................................................................ 57 Site A................................................................................................................................. 57 SiteB................................................................................................................................. 58 SiteC................................................................................................................................. 59 SiteD................................................................................................................................. 59 Site E................................................................................................................................. 61 Summary..........................................................................................................................