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Mr. Roger Schmidt <br /> September 2, 2016 <br /> Page 7 <br /> provides a general indication of the flow rate in the Cache La Poudre River near the location of <br /> the damaged BIC facilities. Estimates of the recurrence intervals corresponding to the flows <br /> measured at the WWTP are provided by the FIS for the location near 8th Avenue, approximately <br /> 1.5 miles upstream from the WWTP gage. Relative to the Cache La Poudre River drainage <br /> basin, there are no major tributaries that enter the river between the damaged BIC pipeline and <br /> the location of the stream gage at the WWTP, nor are there any significant diversions in that <br /> reach of the river. <br /> Cache La Poudre flow data at the WWTP gage are plotted for the time period from August 23, <br /> 2002 through June 22, 2015 (Figure 4). To provide better resolution for the more recent flood <br /> events, flow data are also plotted separately for the time period from January 1, 2013 through <br /> June 22, 2015 (Figure 5). Both Figure 4 and 5 have notations of conditions or events occurring <br /> concurrently with the flow record. As shown on Figures 4 and 5, the estimated flow rate during <br /> the June 2014 flood event was approximately 4,500 cfs. For reference purposes, the 10-year <br /> FEMA flow rate published in the 2016 FIS for the Cache La Poudre River just downstream of 8th <br /> Avenue in Greeley, which is 3,400 cfs, is also shown on Figures 4 and 5. The published 100- <br /> year FEMA flow rate at the same location is 10,700 cfs. <br /> Observations regarding the flow record and the corresponding conditions observed in the subject <br /> area are listed below (Note: all references to measured flow rate are based on the gage located at <br /> the City of Greeley WWTP). <br /> 1. In 2010, the breach of the Boyd-Freeman Ditch occurred at the location where the ditch <br /> turns from east to north (and before the south to north portion of the ditch was changed <br /> from open channel to buried pipe). The breach occurred with a measured flow rate in the <br /> river at the gaging site of approximately 3,500 cfs, or slightly more than the 3,400 cfs 10- <br /> year flow rate published in the FIS (Figure 5). <br /> 2. The June 2014 flood event compared with the September 2013 flood event indicates the <br /> -following main differences (see Figure 5): <br /> a. The June 2014 flood event had a peak flow rate of 4500 cfs, which was higher <br /> than during the September 2013 event(4080 cfs). <br /> b. The June 2014 flood event was of longer duration and had substantially more <br /> volume than the September 2013 runoff event. <br /> c. The June 2014 flood event caused the large headcut on the F street agricultural <br /> field. That compares to the September 2013 event, which also damaged the <br /> pipeline and its embankment but did not cause a headcut on the agricultural field. <br /> 3. In 2015, the measured peak flow rate in the river was 3870 cfs and it was reported that the <br /> water level reached the elevation of, but did not overtop, the concrete bike path. <br /> Consequently, it appears that a flow rate of approximately 4,000 cfs is necessary to <br />