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miles downstream of state Avenue, and a levee system constructed by the U.s. Army Corps of Engineers (USACE). The hydraulic analysis for this revision was performed for the Federal Emergency Management Agency (FEMA), by Foothill Engineering Consultants, Inc., under Contract No. EMW-92-C-3811. An initial Consultation Coordination Officer (CCe) meeting was held in May 1994 and attended by representatives of FEMA, the City of Alamosa, Alamosa County, and Foothill Engineering Consultants, Inc. The streams to be studied and limits of study were identified at this meetlng. The results of this revision were reviewed at a final CCO meeting held on October 22, 1998, and attended by representatives of the City of Alamosa, Alamosa County, and FEMA. All problems raised at that meeting have been addressed in this restudy. The above-referenced levee system consists of channel and tieback levees and was constructed to contain the 100-year flood event. Hydrologic and hydraulic analyses for the same reach as this restudy were performed by the USACE, Albuquerque District, for the Alamosa Local Protection Project (Reference 7). The USACE analytical data were used as a basis for this restudy. The USACE prepared hydrologic reports for the Rio Grande (References 7, 8, and 9) that incorporated gage data with a longer period of record than that used for the November 9, 1982, Flood Insurance study for the City of Alamosa (Reference 10) _ It was determined that differences in the gage analyses in the USACE reports and the Flood Insurance Study for the City of Alamosa (Reference 10) were not statistically significant. Therefore, the discharges from the Flood Insurance Study for the City of Alamosa were used in the revised hydraulic analysis. Analyses of the hydraulic characteristics of the Rio Grande were carried out to provide estimates of the elevations of floods of the selected recurrence intervals (10, 50, 100, and 500 year) along the stream segment studied in detail. Individual water- surface profiles were developed using the USACE HEC-2 computer program (Reference 11). Digitized cross sections were developed by photogrammetric methods (Reference 12) and were modified, repeated, or adjusted for bridges, diversions, and other general features in order to compute the significant backwater effects of all structures and features. Between cross sections, the 100-year flood plain boundaries were interpolated using topographic mapping at a scale of 1:2,400 (Reference 12). Channel roughness factors (Manning's "nUl ranging from 0.029 to 0.045 and overbank roughness factors ranging from 0.030 to 0.065 were used to perform the hydraulic analysis. The floodway along the Rio Grande was determined using the USACE HEC-2 computer program (Reference 11). Floodway widths were computed at cross sections. Between cross sections, the floodway boundaries were interpolated. The results of the floodway computations are tabulated for selected cross sections (see Table 1, "Floodway DataU). The channel levee is coincident with the floodway limit along the right overbank. 17