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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />II <br />I <br />i I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />(FISl for Rock Rapids, Iowa. Appendix A contains backup data for the <br />hydrologic analysis for this portion of the study. <br />Peak discharges were computed for Rock River and two of its <br />tributaries, Moon Creek and Tom Creek, using the Iowa statewide regression <br />equations (U.S. Geological Survey (USGSl, 1993l and the Minnesota <br />regional regression equations (USGS, 1987l. The computed peak discharges <br />obtained from both sets of regression equations are presented in table 1. <br /> <br />Gaging records for the gaging station at Rock Rapids were available <br />from 1960 to 1974. A statistical analysis was performed using the Corps <br />of Engineers HEC-FFA computer program which reflects techniques described <br />in Bulletin 17B. The gaging station in Rock Rapids is located just <br />downstream from the Moon Creek confluence. The computed and expected <br />frequency-discharge relationships, as shown in the HEC-FFA output file <br />for Rock River at Rock Rapids, are also presented in table 1. <br /> <br />The effective FIS for Rock Rapids contains frequency-discharge data <br />for two locations on the Rock River within Rock Rapids. The methodology <br />used to develop these peak discharges is described in Section 4.0 of the <br />FIS as follows: <br /> <br />"Using a historic period of 60 years, station statistics were <br />adjusted using guidelines set by Bulletin No. 17B. The <br />resulting frequency curve was significantly lower than the <br />curve obtained without historic adjustment. Regional U.S. <br />Geological Survey equations were also used to estimate flow <br />frequency values." <br /> <br />Peak discharges as published in the FIS are also included in table 1 for <br />comparison purposes. <br /> <br />16 <br />