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.. " The Honorable Edward J. Tagliente, Mayor June 5, 1998 Page two In the CLOMR packet we received from you the applicant provided a map showing the outline of the FEMA approximate floodplain and also showing the" I 00- Year Pre-Project Delineation" as determined by his engineering analysis. The "Pre-Project Delineation" is the actual floodplain delineation for conditions in the field today, based on Mr. Smith's detailed study. That "Pre-Project Delineation" shows an existing floodplain that is substantially wider than the FEMA approximate floodplain for Godding Hollow. ProDosed FloodDlain The map submitted by the applicant also shows the "IOO-Year Post-Project Delineation", which is the delineation of the floodplain as it would look after the project was constructed, including the parallel side-spill channel. That floodplain would have the same boundary as the FEMA approximate floodplain along its eastern edge. Along its western edge it would actually be narrower than the FEMA approximate floodplain. A substantial area of land would be removed from the actual floodplain by physically changing it to correspond to the FEMA approximate floodplain. That land, which is currently the eastern portion of the actual floodplain, would be removed from the floodplain by filling, along with the construction of the parallel side-spill channel. The sketch plan included in the packet shows approximately 28 residential lots in that land. In addition, some open space and an athletic area to include ballfields would be provided. The 28 lots, the open space and the ballfields would be on the fill. Comments I) Need to provide additional technical information Our first comment has to do with the technical information included in the packet sent to us. There was no verbal explanation of the methods used to determine the detailed floodplain. There was no discussion of the hydrologic analysis, to explain the technique(s) used to calculate the 100-year flow at the site. The floodplain map did not show the computed 100-year flood elevations. There were no water surface profiles showing a profile view of the 100-year flood elevations at the site. Copies of the current FEMA floodplain maps for Frederick and for unincorporated Weld County, showing the relation of the information generated by the applicant to the FEMA information, were not provided. We trust that all of those. materials will be part of the LOMR packet once the project has actually been built 2) Explanation of functioning of side-spill channel Our second comment relates to the side-spill channel. Through the southern half of the property, going from Weld County Road 18 north toward Cross-Section 12 (in the middle of the property) the cross- sectional drawings show high ground between the two channels (the existing channel and the new side-spill channel), There is no explanation of how floodwater would get from one channel to the other, given the high ground separating them from each other. Such an explanation would help us understand the project better.