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effect and overbank flows. As floodflows increase, masses of debris may break loose from one bridge and cause a wall of water and debris to surge downstream to another obstruction. In some instances, debris may collect and cause structural damage. The Town of Holyoke has little history of flooding. Information on historical floods that have occurred in the study area is limited to that on historical rainfalls and in newspaper files. Stream-gaging stations (Reference 3) within the Frenchman Creek basin (Table 1) show a limited flood history. The following information on historical rainfall was taken from newspaper accounts in the Holyoke Enterprise on July 26, 1963 (Reference 4): Five-inch rain at Amherst; 3.21 inches on government gage at Holyoke (mostly within 1 hour); 3.5 inches at other places in Holyoke; 2.5 inches at Sterling flooded basements and some general stores; 2.5 inches east of Holyoke; 2 inches 4 miles south of Holyoke. One of the heaviest rainfalls ever experienced in Holyoke over such a short period of time (less than 1 hour). Mentioned damage to one home in Amherst but nothing at Holyoke. 2.4 Flood Protection Measures No flood-control structures exist in the Town of Holyoke. 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 equaled or exceeded once on the average during any 10-, 50-, 100-, or 500-year period (recurrence interval) have been selected as having special significance for flood plain management and for flood insurance rates. These events, commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equaled 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 intervals 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 exceedence) in any 50-year period is approximately 40 percent (4 in 10), and, for any 90-year periOd, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes. 5