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 Page 12 Upper and Lower Emerald Valley Dam Failure Report January 23, 2015 Figure 14: Comparison of Sept 2013 Storm to NOAA Atlas 14 Precip Frequency Estimates The above intensity data shows clearly that the Sept. 2013 storm was not extremely intense. The maximum hourly intensity in the storm has less than a 1-year Average Recurrence Interval (ARI) by NOAA Atlas 14. However, the Sept 2013 storm event was a long slow rain: the 48-hour total for Sept 12 and 13 for Little Fountain Creek Above Highway 115 are just below a 500-YR ARI. Figure 14 plots observed rain totals for Little Fountain Creek at various durations (maximum total for each duration) along with NOAA Atlas 14 (NA 14) frequency estimates (full NOAA Atlas 14 tabular data are include in Appendix D). Figure 14 shows the Sept 2013 maximum 15 minute, 1 hour, and 6 hr rains were well below the NA 14 100-YR estimate. For the 24-hour duration the Sept 2013 rain was approximately equal to the NA14 100-YR estimate. The maximum observed 48-hr total was between the NA 14 100-YR and 500-YR estimates. 7.2 Model Setup & Calibration The results of the field investigations, basin delineation, and rainfall data analysis all provide important parameters to be able to model the physical system of the basin as rain falls and water runs off into the stream networks. Those previously discussed parameters are all fixed once determined. However, unit hydrographs, basin loss parameters, channel routing parameters, and dam breach parameters are all more subjective. This results in an iterative process being utilized to select the most appropriate values of each of these parameters. This process is referred to as the “calibration phase” of the modeling. The hydrologic literature typically assigns ranges of appropriate values for these parameters. In the modeling process an initially assumed set of parameters is utilized; the model is run and then the modeled outflow values are compared to those calculated through indirect methods at locations of interest. The parameters determined to be sensitive, meaning their small change results in significant changes in model results, are modified, staying within the appropriate ranges, until the model results compare favorably with the measured flows at those sections of interest, the calibration sections.