Estimates of Peak Flood Discharge for 21 Sites in the Front Range in Colorado in Response to Extreme Rainfall in September 2013: U.S
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Estimates of Peak Discharge for 21 Sites in the Front Range in Colorado in Response to Extreme Rainfall in September 2013 Scientific Investigations Report 2016–5003 U.S. Department of the Interior U.S. Geological Survey Cover photograph. Floodwater was still spilling out from Twomile Creek onto Linden Avenue on September 15, 2013, in North Boulder, Colorado. The effects of several landslide/debris flows generated by saturated conditions during the night of September 11–12 can be seen on Dakota Ridge near the center of the photograph. Estimates of Peak Discharge for 21 Sites in the Front Range in Colorado in Response to Extreme Rainfall in September 2013 By John A. Moody Scientific Investigations Report 2016–5003 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Director U.S. Geological Survey, Reston, Virginia: 2016 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Moody, J.A., 2016, Estimates of peak flood discharge for 21 sites in the Front Range in Colorado in response to extreme rainfall in September 2013: U.S. Geological Survey Scientific Investigations Report 2016–5003, 64 p., http:// dx.doi.org/10.3133/sir20165003. ISSN 2328-0328 (online) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................5 Description of Study Area ...................................................................................................................5 Field Methods .................................................................................................................................................6 Indirect Discharge Calculations ..................................................................................................................7 Cowan Method ......................................................................................................................................7 Jarrett Method ......................................................................................................................................7 Empirical Method ................................................................................................................................10 Critical Flow Method ..........................................................................................................................10 Slope-Area Method ............................................................................................................................10 Bagnold Method..................................................................................................................................10 Measured “n” Method .......................................................................................................................12 Yochum Method ..................................................................................................................................12 Comiti Method .....................................................................................................................................12 Sediment-Transport Effect ................................................................................................................12 Rainfall Intensity Calculations ...................................................................................................................14 Estimates of Peak Discharge .....................................................................................................................14 North St. Vrain Creek above Highway 7 Bridge .............................................................................15 North St. Vrain Creek above Apple Valley Bridge .........................................................................17 South St. Vrain Creek above Confluence with Middle St. Vrain Creek ......................................19 South St. Vrain Creek below Confluence with Middle St. Vrain Creek ......................................21 Little James Creek above Confluence with James Creek ...........................................................23 James Creek above Jamestown ......................................................................................................25 James Creek below Jamestown ......................................................................................................27 Left Hand Creek below Nugget Gulch .............................................................................................29 Left Hand Creek at Buckingham Park .............................................................................................31 Fourmile Canyon Creek at 491 Wagonwheel Gap .........................................................................33 Twomile Canyon Creek at 215 Linden ..............................................................................................35 Fourmile Creek above Long Gulch ...................................................................................................37 Long Gulch above Loretta-Linda ......................................................................................................39 Loretta-Linda at Flume 9–1 ................................................................................................................41 Sugarloaf ..............................................................................................................................................43 Fourmile Creek at Logan Mill ............................................................................................................45 Boulder Creek at Mouth of Boulder Canyon ..................................................................................47 Gregory Creek below Long Canyon .................................................................................................49 Gregory Creek at Rest Area ..............................................................................................................51 Bluebell Canyon Creek above Mesa Trail Crossing ......................................................................52 Bear Canyon Creek above Bear Mountain Drive ..........................................................................55 Discussion .....................................................................................................................................................57 Relation between Peak Discharge and Rainfall Intensity ............................................................57 Comparison with Maximum Worldwide Floods .............................................................................57 Sediment Transport Effects ...............................................................................................................58 iv Summary........................................................................................................................................................61 Acknowledgments .......................................................................................................................................61 References Cited..........................................................................................................................................62 Figures 1. Maps showing location of the Front Range, study area, indirect measurement sites, and rain gages ....................................................................................................................3 2. Graph showing cumulative rainfall for select Urban Drainage and Flood Control District rain gages during September 9–16, 2013, along the Front Range in Boulder County, Colorado ............................................................................................................4 3. Photograph showing turbulent flow in James Creek through Jamestown, Colorado, on September 12, 2013 ...............................................................................................5 4. Graph showing comparison of measure effective Manning’s n and variable power law resistance equation estimate of effective Manning’s n ...................................11 5–24. Photographs showing 5. Typical examples of erosion and deposition of sediment from the September 2013 floods, Boulder County, Colorado ......................................................13 6. North Saint Vrain Creek above Highway 7 Bridge .......................................................15 7. North Saint Vrain Creek above Apple Valley Bridge