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4.3 Review in the Field The draft maps were reviewed in the field with local staff and residents. At the same time the approximate cross-sec:tions were reviewed, and the preliminary hyclraulic calculations were revised. On the basis of all of these steps the depths of flooding listed in Table 8 were selected for the various ~tream reaches in Costilla County. In the field the basic question w~s asked, "Does the combination of depth and width of flooding, in conjunction with the estimated velocity of flow, make sense for this particular stream reach?" Revisions were made both to the depth of flooding shown and to the delineated floodplain boundaries. In addition, in more urbanized areas, topographic details ttAat were lacking on the base maps were taken into account in finalizing the delineations. For the area immediately around the Town of San Luis, such a field review was not necessary. The December 1988 detailed study had already been field checked before it was finalized. That study was coordinated with the Ch~CB, so no further review was conducted. On the Rio Grande a cursory field review of 5elected portions of the CSU floodprone maps was conducted. By and. large, however, those maps were assumed to have been field checked during their own preparation process. Because they were based on gage analyses and rating curves developed for field-surveyed cross-sections before they were ever field checked, further field review was not deemed to be necessary. 4.4 Flooded Areas Once all of the field review was complete, it was time to finalize the maps. In most cases that meant drafting flood boundaries that were slightly narrower than Lhose shown on the first draft maps. Where the field review indicated that the floodplain was too wide on one side of the stream, an attempt was made to assure that flood elevations were essentially equal on both sides, within the limits of accuracy of the topographic mapping. In several instances, roads and other features were found to be hiqher in the field than the base maps led one to believe. The maps were corrected, where appropriate, to show such areas as being outside the floodplain or as islands within the floodplain. -31-