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<br />I <br />I <br />I <br />I <br />I <br />'I <br />I ' <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />which drains the detention area, The volume provided behind the roadway embankment prior to <br />overtopping is 82 acre-feet with a maxirilum release rate of 90 cfs from the existing siphon. The' <br />lOa-year existing conditions discharge is estimated to be 1,230 cfs which corresponds to a storage <br />volume of 107 acre-feet and an overtopping depth of approximately 0,6 feet, <br />I-25/WCR 18 Pond This detention pond is an existing storage area located on a minor <br />tributary to Godding Hollow approximately 1,000 feet south of Weld County Road 18 and <br />immediately west of 1-25. The roadway embankment associated with 1-25 and its frontage roads <br />is elevated approximately 10 feet above the invert of the existing 36-inch culvert which drains the <br />detention area. An additional 24-inch culvert, located approximately 3 feet above the 36-inch <br />culvert, also drains the detention area. The volume provided behind the roadway embankment <br />prior to overtopping is 170 acre-feet with a maximum release of 140 cfs through both culverts. <br />The lOa-year existing condition discharge is estimated to be 100 cfs which corresponds to a <br />storage volume of 74 acre-feet. During the laO-year existing condition event, the frontage road <br />is overtopped by as much as 3 feet, but I-25 does not overtop, <br />UPRR Spur Pond This detention facility is an existing pond located on a tributary to the <br />main Godding Hollow channel, approximately 1,800 feet north of WCR 8 and approximately 800 <br />feet west ofI-25. The railroad spur embankment is elevated approximately 14.4 feet above the <br />invert of the existing 6,5-foot CMP which drains the detention area, The volume provided behind <br />the railroad spur embankment prior to overtopping is 26 acrecfeet with a maximum release rate <br />of 530 cfs. The lOa-year existing condition discharge is estimated to be less than 800 cfs, This <br />facility was not incorporated into the existing condition modeling effort due to the temporary <br />nature of the railroad spUr. <br /> <br />3.1.2 Tn-Town Rasin <br /> <br />No existing detention facilities were located on the major drainageway in the Tri-Town <br />Basin. However, ponding behind one existing embankment is effective in reducing the lOa-year <br />peak discharge to the downstream subbasins. This detention area consists of two ponds closely <br />located to each other and adjacent to the railroad embankment between Weld County Road 22 and <br />Weld County Road 24 as shown on Sheet 1. At the two ponding locations, the combined volume <br />behind the railroad embankment is estimated to be 61 acre-feet with a combined release rate of <br />approximately 190 cfs prior to overtopping of the embankment. During the lOa-year existing <br />condition event, the maximum storage volume behind the embankment is 41 acre-feet with a <br />release rate of approximately 120 cfs. <br /> <br />T:\QPEMCOWf!l401IcoweldOf fnlrpt.wpd <br /> <br />3.5 <br /> <br />September 8, 1999 <br />