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Table of Contents <br />EXECUTIVE SUMMARY ........................................................................................................... ..............................i <br />Tableof Contents ................................................................................................................. <br />..............................3 <br />1 INTRODUCTION ............................................................................................................ <br />..............................1 <br />2 BIG PICTURE OF THE EVENT ......................................................................................... <br />..............................2 <br />3 BACKGROUND ON DAMS ............................................................................................. <br />..............................3 <br />4 PERFORMANCE OF DAMS DURING THE SEPTEMBER 2013 EVENT <br />.............................. ..............................5 <br />5 PURPOSE AND SCOPE OF THE INVESTIGATION ............................................................ <br />..............................5 <br />6 THE LITTLE THOMPSON RIVER BASIN STUDY AREA ...................................................... <br />..............................7 <br />7 BIG ELK MEADOWS DAMS DESCRIPTIONS ................................................................... <br />..............................8 <br />7.1 Sunset Lake ........................................................................................................... <br />..............................9 <br />7.2 Rainbow Lake ........................................................................................................ <br />..............................9 <br />7.3 Willow Lake ........................................................................................................... <br />..............................9 <br />7.4 Mirror Lake ........................................................................................................... <br />..............................9 <br />7.5 Meadow Lake ....................................................................................................... <br />..............................9 <br />8 FAILURE EVENT AND EMERGENCY RESPONSE ............................................................ <br />.............................10 <br />9 DAM FAILURES ............................................................................................................. <br />.............................12 <br />10 ANALYSES OF THE FLOOD AND DAM FAILURES ...................................................... <br />.............................13 <br />10.1 Introduction ......................................................................................................... <br />.............................13 <br />10.2 Rainfall Spatial Distribution Analysis ................................................................... <br />.............................14 <br />10.3 Field Investigation Surveys and Data Collection .................................................. <br />.............................15 <br />10.4 Vertical Elevation Datum and Units ..................................................................... <br />.............................19 <br />10.5 Basin Delineation ................................................................................................. <br />.............................20 <br />10.6 Rainfall Temporal Distribution Analysis ............................................................... <br />.............................21 <br />10.7 Model Calibration ................................................................................................ <br />.............................22 <br />10.8 Unit Hydrographs ................................................................................................. <br />.............................23 <br />10.9 Subbasin Loss Rates ............................................................................................. <br />.............................24 <br />10.10 Hydrologic Channel Routing ............................................................................ <br />.............................24 <br />10.11 Overtopping Failure Breach Parameters ......................................................... <br />.............................25 <br />10.12 Model Calibration Cross Sections .................................................................... <br />.............................26 <br />11 FINAL MODEL RESULTS ............................................................................................ <br />.............................27 <br />Report of the September 2013 Little Thompson River Flooding <br />COLORADO <br />and Big Elk Meadows Dam Failures, June 2014 (Revised, Dec 2014) <br />Division of Water Resources <br />DAM SAFETY BRANCH <br />