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I . I I I I I I I I I I I I I I I I I I DESCRIPTION OF EXISTING FLOOD PROBLEMS The flood problems at Rock Rapids result from rapid spring snowmelt as well as heavy, intense rains which primarily occur during the summer months. Nuisance flooding from frequent rainfall events does not seem to be a problem in Rock Rapids, however, the area known as Island Park is one of the most flood prone locations within the city and experiences occasional flooding. Overbank flows along the Rock River causing any significant flood damage to structures may not occur until about the so- year event. EXPECTED FUTURE VITHOUT-PROJECT CONDITIONS Future development within Rock Rapids is expected to be minimal. Therefore, the expected future without-project conditions in Rock Rapids are assumed to be the same as the existing conditions for the purposes of this study. Highway, bridge, or channel modifications in the city are not planned at this time, therefore flood depths or interior flood discharges would not be affected. In addition, it is expected that very little future development that would impact hydrology will take place within the Rock River basin. HYDROLOGIC ANALYSIS Hydrologic analyses were performed in order to develop peak discharge-frequency relationships for the Rock River, Moon Creek, and Tom Creek at Rock Rapids, Iowa. Discharges were computed using Iowa statewide regression equations and Kinnesota regional regression equations for three locations along the Rock River, as well as for Koon Creek and Tom Creek. In addition, gaging records were used to develop peak discharges for one location on the Rock River using the Bulletin 17B (Vater Resource Council, 1981l Methodology. Computed discharges were then compared to those published in the Kay 1991 Flood Insurance Study 1S