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September 2, 1938. "Parts of the residential area in Louisville were under several inches of water, but the business district was not damaged. One person was killed in an automobile accident on the flooded highway east of Louisville. The bridge at Empire Drive and State Highway 42 was on the verge of failure, but was saved." . June 9, 1949. "The bridge at the junction of Coal Creek and Rock Creek, 3 miles north and 1/4 mile west of Erie waS threatened and closed to traffic. The bridge over Coal Creek, 3/4 mile east of Superior, went out." May 1969. "Damage to land irrigation structures and agriculture totalled approximately $75,000." 2.4 Flood Prutection Measures No flood protection structures exist or are planned within and adjacent to the City of Lafayette. The City of Lafayette has building ordinances along the flood plains which prohibit certain types of construction. 3.0 ENGINEERING METHODS For the flooding sources studied in detail in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude which are expected to be equalled or exceeded once on the average during any 10-, 50- , 100-, or SOO-year period (recurrence interval) have been selected as having special significance for flood plain management and for flood insurance premium rates. These events, commonly termed the 10-, 50-, 100-, and SOO-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equalled or exceeded during any year. Although the recurrence interval represents the long term average period between floods of a specific magnitude, rare floods could occur at short inter- vals or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood which equals or exceeds the 100-year flood (1 percent .chance of annual occurrence) in any 50-year period is approxi- mately 40 percent (4 in 10), and, for any 90-year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported here reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood eleva- tions will be amended periodically to reflect future changes. 3,1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge- frequency relationships for floods of the selected recurrence inter- vals for each stream studied in detail in the community. 5