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. . . The difference in elevation between the ground at the low point on the "spillover" ridge and the ground at the top of the railroad embankment is approximately 5 feet. That low point is approximately 2.5 feet lower than the lO-year water surface elevation computed by EPI and approximately 6 feet lower than the 100-year water surface elevation computed by EPL A spill that was either 2.5 feet deep (lO-year flow) or 6 feet deep (IOO-year flow) would be substantial. It is likely that taking into account the effect of spills over the low point will result in significant changes both for the 10-year flood and for the 100-year flood. For that reason, the revised FIRM is deemed to be acceptable only as approximate floodplain information. Any development in the south side approximate floodplain will need a detailed floodplain analysis to assure that the effects of spills over the low point of the ridge have been appropriately considered. On the north side of Otis, but still along the Southwest Drainage, where the flood control project was constructed, the CWCB used the Norton, Underwood & Lamb map to update the floodplain to properly reflect that project. The CWCB also did make a change to the town corporate limits in the southeast comer of Otis, with the help of the town clerk, to more appropriately represent floodprone areas within the current town boundaries. It is expected that the town will conduct the necessary hydraulic analysis to prepare a detailed floodplain map to replace the revised FIRM in the near future. The Town of Otis should regulate the approximate floodplains on a case-by-case basis. An approximate floodplain analysis can be submitted by a developer or development proponent for the allowable cases. Those allowable cases include development such as open space, agriculture, farm bridges, pole barns and individual residential structures. A detailed floodplain analysis must be performed by a professional engineer and submitted by the development proponent for all other projects. The use of approximate floodplain information is not appropriate for development involving residential subdivisions greater than 50 lots or occurring on sites greater 5 acres, commercial construction, industrial construction, construction of public facilities, or construction of flood control facilities. Copies of the FIRM, prepared by FEMA, and the revised FIRM, prepared by the CWCB, are included in Appendices 3 and 4. 8