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Willow Reservoir level as a result of the subsequent failure of the upstream Rainbow dam overwhelmed both "spillways" and exploited an apparent low area in the embankment crest, resulting in the embankment breach as observed during the forensic investigation field work. This also explains the negative values for overtopping depth for Willow dam shown in Table 12. 11.3 Flood Volumes The rainfall data shown previously describes the aerial and temporal extents of the rainfall over the study basin. Table 13 below shows the rainfall depths in the sub - basins, the total volume of rainfall that fell during the event and the rainfall that was not absorbed by the soils in the basin and produced the damaging runoff. Table 13 — Rainfall Depths and Rainfall and Runoff Volumes The HEC -HMS modeling shows the timing of the flows from the basins and the volumes of water behind the dams at the time of their failure. Due to the overtopping that was occurring at the time of failure, the total volume of water released from the failed dams is slightly higher than the maximum volumes shown in Table 2. Table 12 shows the volume of water released from each dam during the breaches with a cumulative total of 251 acre feet. Table 13 shows the average rainfall depths over each of the basins in the study, the total volume of water that fell and the total volume of water modeled as runoff. Comparing the total storm runoff volume to the volume of water released from the dams shows the dam breaches were 1.2% of the total volume of runoff that occurred during the entire period of flooding. As was discussed in the public meeting on March 29, 2014, the reservoir volume release equates to the volume of approximately 125 Olympic —sized swimming pools while the volume of runoff from the entire storm is approximately 10,435 Olympic -sized pools. Report of the September 2013 Little Thompson River Flooding COLORADO and Big Elk Meadows Dam Failures, June 2014 (Revised, Dec 2014) A&V Division of Water Resources Page 34 of 48 - - ■ 9go rm:1ovilH41:1 Basin Average Rainfall Runoff % of Total Suhbasin Rainfall Depth (in) Volume (ac -ft) Volume (ac -ft) Runoff West Fork Little Thompson River Upstream of Meadow Dam (SB 3a, 3b) 14.44, 13.55 15,116 6,655 31.9% Little Thompson River, Upstream of U5 36 (SB 2b) 11.64 11,044 3,513 o 16.8/0 West Fork Little Thompson River, Meadow Lake to U5 36 (SB 2c) 13.84 4,030 1,791 8.6% West Fork Little Thompson River, U5 36 to North Fork (SB 2a) 13.73 5,529 2,487 11.9% North Fork Basin (SB 4) 11.80 17,525 5,707 27.4% Rowell Gulch Basin (SB 1) 10.46 2,228 717 3.4% Totals 55,472 20,570 100% The HEC -HMS modeling shows the timing of the flows from the basins and the volumes of water behind the dams at the time of their failure. Due to the overtopping that was occurring at the time of failure, the total volume of water released from the failed dams is slightly higher than the maximum volumes shown in Table 2. Table 12 shows the volume of water released from each dam during the breaches with a cumulative total of 251 acre feet. Table 13 shows the average rainfall depths over each of the basins in the study, the total volume of water that fell and the total volume of water modeled as runoff. Comparing the total storm runoff volume to the volume of water released from the dams shows the dam breaches were 1.2% of the total volume of runoff that occurred during the entire period of flooding. As was discussed in the public meeting on March 29, 2014, the reservoir volume release equates to the volume of approximately 125 Olympic —sized swimming pools while the volume of runoff from the entire storm is approximately 10,435 Olympic -sized pools. Report of the September 2013 Little Thompson River Flooding COLORADO and Big Elk Meadows Dam Failures, June 2014 (Revised, Dec 2014) A&V Division of Water Resources Page 34 of 48 - - ■ 9go rm:1ovilH41:1