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<br />Nissen Reservoir No. 2 Downstream Channel <br /> <br />The January 25, 1994, LOMR was issued to reflect the effects of the <br />relocation of the Nissen Reservoir No. 2 spillway and the <br />construction of Nissen Reservoir No. 2 Downstream Channel, as shown <br />on FIRM Panel 0020. Due to the relocation of the Nissen Reservoir <br />No. 2 spillway, the Special Flood Hazard Area (SFHA) from just <br />downstream of the intersection of Main street and Miramonte <br />Boulevard upstream to Nissen Reservoir No. 2 was removed. In <br />addition, the SFHA along Nissen Reservoir No. 2 Downstream Channel, <br />located approximately 700 feet west of Eagle Road, was added to the <br />FIRM from the confluence with Nissen Reservoir Channel upstream to <br />Nissen Reservoir No.2. This increase in the SFHA is entirely <br />contained within a city of Broomfield drainage easement. <br /> <br />A revised hydraulic analysis was performed by S&G using the USACE <br />HEC~2 computer program (Reference 23). Cross-section data for the <br />revised analysis were obtained from post-construction field surveys <br />and the starting water-surface elevations were determined using the <br />slope-area method for Nissen Reservoir No. 2 Downstream Channel. <br />The results of the analysis are presented in the report entitled, <br />"Nissen Reservoir No. 2 Downstream Golf Course Channel Floodplain <br />Analysis," prepared by S&G, dated July 1992 and revised October <br />1993(Reference 24). <br /> <br />As a result of the revisions, the floodplain boundary delineations <br />and zone designations of the base flood have been modified along <br />Nissen Reservoir No.2 Downstream Channel. In addition, the SFHA <br />from just downstream of the intersection of Main Street and <br />Miramonte Boulevard upstream to Nissen Reservoir No. 2 was removed. <br />Topographic work maps at a scale of 1:600, with a contour interval <br />of 1 foot~ produced by S&G, and dated December 6, 1991 (Reference <br />25), were used to develop the new boundaries as shown on revised <br />FIRM Panel 0020, <br /> <br />Citv Park Channel <br /> <br />The August 2~ 1995, LOMR was issued to reflect the effects of a <br />channelization project and construction of culverts at Alter and <br />Burbank Streets and two private drives along City Park Channel, as <br />shown on FIRM Panel 0015. This revision affects the area from just <br />upstream of U.S. Highway 287 (South 112th street) to approximately <br />2,850 feet upstream of U.S. Highway 287. <br /> <br />The revised hydraulic analysis was performed by Greenhorne & O'Mara, <br />Inc., using the USACE HEC-2 computer program (Reference 20). Cross- <br />section data for the revised analysis were obtained from post- <br />construction field surveys and the starting water-surface elevations <br />were taken from the original study. The roughness coefficients <br />(Manning's "n" values) were changed to reflect field observations <br />and channelization. The "nN values changed from 0.06 to 0.03 for <br />the channel and from 0.05 to 0.04 for the overbanks. The results of <br />the analysis are presented in the report entitled "Request for a <br />Letter of Map Revision for City Park Channel, City of Broomfield, <br />Colorado," prepared by Greenhorne & O'Mara, Inc., and dated October <br />1994 (Reference 26). <br /> <br />As a result of the revisions, the BFEs and floodplain and floodway <br />boundary delineations were modified along City Park Channel from <br />just upstream of u.s. Highway 287 (South 112th Street) to <br />approximately 2,850 feet upstream of U.S. Highway 287. The SFHA <br />shifted to the south by a maximum of 150 feet along the revised <br /> <br />35 <br />