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4.3 Review in the field The information from the San Luis area study was simply transfe!red to the San Luis 7 1/2 minute Quadrangle map. The final approximate delineations outside the San Luis area were tied in to the detailed delineations within the San Luis stuny area. A similar process was followed for the Rio Grande delineations prepared by the CSU team. The draft maps were reviewed in the field with local staff and residents. At the same time the approximate cross-sections were reviewed, and the preliminary hydraulic calculations were revised. On the basis of all of these steps the depths of floodin'l listed in Table 8 were selected for the various stream reaches in costilla County. The Index of floodf'd Area Maps (see Plate 1) shows the entire county and the location of the specific plates that inclUde floodplain delineations, as well as a schematic representation of the stream reaches that were studied. The Flooded Area Maps themselves (see Plates 2_22) follow the index. In the field the basic question was 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 that 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 CWCB. so no further review was conducted. On the Rio Grande a cursory field review of selected 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 ratin'l curves developed for field-surveyed cross-sections before they were ever field checked. further field review was not deemed to be necessary. 4.4 F'looded Areas I I I I i' , , , ~ 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 those 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 esaentially equal On both sides, within the limits of accuracy of the topographic mapping. In several instances. roads and other features were found to be higher in the field than the base maps led one to believe. The maps were corrected. where appropriate. to show such areas as bein'l outside the floodplain or as islands within the floodplain. " , _31~ _32_