4.0 COMPUTER MODELINGA comprehensive hydrologic model of the watershed, utilizing the US Army Corps of Engineers (USACE) computer model HEC-HMS, was developed to simulate stormwater runoff and evaluate potential solutions to flooding problems along Big Cicero Creek. Parameters for the model were derived from representative cross-sections from the two-foot contour mapping of Big Cicero Creek, Hamilton County one-foot contour mapping, and drain reconstruction plans for Cox Regulated Drain, Dixon Creek, Crum Drain, and tributaries. Subbasins were delineated using the Hamilton County one-foot contour mapping or the USGS quad 10-foot contour interval mapping in Tipton, Boone, and Clinton Counties. Because historic high water marks were available for the June 1957 and January 1962 flood events, rainfall data for the corresponding dates was obtained from the National Oceanic and Atmospheric Administration (NOAA) for gages in Burlington, Tipton, Anderson, Lebanon, Hartford, Noblesville, and Frankfort. The June 1957 flood discharge at the Big Cicero Creek at Arcadia gage was close to a 100-year frequency storm. The 1962 flood was between a 5- and 10-year frequency storm. For the frequency storms, the NOAA Atlas 14 rainfall depths and 24 and 48 hour distributions were specified. The computer model was calibrated to the June 1957 and January 1962 events within the limits of available data and model capabilities. A more detailed explanation of the hydrologic modeling process is included in Volume 2 of this report. New values for the frequency discharges used in the FEMA Flood Insurance Study (FIS) models were determined to be necessary. These values are listed in Volume 2. A new hydraulic model, utilizing USACE computer model HEC-RAS, was developed from about 3,000 feet downstream of the Tobin Ditch confluence upstream to County Road 500 West (approximately 7 miles) to calculate existing flood profiles and also to evaluate the impact of proposed flooding solutions. Cross-section geometric data for the hydraulic model was taken from the 2-foot contour mapping of Big Cicero Creek generated by EarthData, supplemented with field surveyed channel cross sections by staff from the Hamilton County Surveyor’s Office. The USGS quad maps were used for additional data beyond the limits of the 2’ contour mapping. Bridge information was taken from the Tipton County Bridge Inventory, Indiana Department of Transportation (INDOT) plans for the SR 19 bridge, and field measurements. The model was calibrated to the June 1957 and January 1962 high water marks provided by IDNR. Based on this model, the area along the study reach that was inundated by the 1962 flood was more than 1,400 acres. Based on an analysis of the stream gage data for Arcadia, that flood was between a 5- and 10- year frequency flood. Exhibit 1 shows the area inundated by the 2-, 10-, and 100-year floods under existing conditions. A more detailed description of the hydraulic model is included in Volume 2. An unsteady flow model for the stream reach was also developed using the HEC-RAS unsteady flow model option. This model used hydrographs at different points along the stream from the HEC-HMS model for the frequency discharges combined with the cross section data used in the hydraulics model. The unsteady flow model provided a method of including the timing aspect of flooding along different reaches of the stream to be factored in. This allowed rough analysis of the effect of various alternatives on the time that flood waters would be expected to be out of banks. This effect is of special interest in evaluating alternatives that would benefit the agricultural lands.
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