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version 8i. Soil information was obtained from the Natural Resources Conservation Service (N RCS) <br />Geospatial Data Gateway. ESRI ArcMap 10.0 was used for processing Geographic Information <br />System (GIS) mapping and spatial information. The Colorado Dam Safety Branch guidance <br />documents; Guidelines for Dam Breach Analysis (2010), Guidelines for Hazard Classification (2010), <br />and Hydrologic Basin Response Parameter Estimation Guidelines, (2008), were also used as <br />references for the analyses. <br />10.2 Rainfall Spatial Distribution Analysis <br />Analysis of a design precipitation event on a drainage basin to evaluate the appropriate size <br />spillway for a dam is a fairly common exercise performed by the Dam Safety Branch and is typically <br />conducted with a high level of confidence. However, analyzing the occurrence of a given <br />precipitation event and accurately modeling the resulting runoff requires collecting and <br />assembling data from the actual physical processes and is inherently more difficult. <br />In order to accurately model the storm runoff, the Dam Safety Branch contracted with Applied <br />Weather Associates, Inc. (AWA) to obtain rainfall data from the 1:05 am MDT on September 8 to <br />1:00 am MDT on September 18, 2013 to capture the full extent of the storm. Figure 8 below <br />shows the results of the AWA analysis for the study area basins. The rainfall analysis process <br />involved analyzing radar images for the storm event and calibrating them to gages that measured <br />the rainfall as it actually fell. This product is referred to as gage- adjusted Radar rainfall. The study <br />area had a good density of rain gages to facilitate the adjustment process. The density of gages <br />available to calibrate radar images provides a high level of confidence in the results of the analysis. <br />Figure 8—Gage-adjusted Radar rainfall analysis resultsfor the Little Thompson River study area (from AWA, 2014. See <br />Figure 17for add itionaI local landmarks) <br />Report of the September 2013 Little Thompson River Flooding COLORADO <br />and Big Elk Meadows Dam Failures, June 2014 (Revised, Dec 2014) a Division of Water Resources <br />Page 14 of 48 D pirtm._nt or r.a,ur,r s,,sourc�, <br />DAM SAFETY BRANCH <br />