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<br />, <br />t <br />. <br />. <br />. <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />. <br />. <br />t <br />. <br />. <br />t <br />t <br />t <br />t <br />. <br />. <br />t <br />t <br />. <br />. <br />. <br />. <br />t <br />t <br />t <br />. <br />. <br />t <br />. <br />. <br />. <br /> <br />1.0 PROJECT OVERVIEW <br /> <br />The Davis No.1 Dam Outlet Works and Spillway Rehabilitation was designed and constructed to <br />safely pass the flood resulting from a rainfall event equal to 50 percent of the Probable Maximum <br />Precipitation (PMP) and to replace the deteriorated outlet works pipe. Davis No.1 is located in <br />Section 11/ Township 1 North, Range 70 West in Boulder County, Colorado, and is the largest of two <br />adjacent reservoirs (Davis NO.1 and Davis No.2), commonly referred to as Twin Lakes. Both <br />reservoirs are owned by Boulder and Left Hand Irrigation Company and are operated as "equalizers" <br />for irrigation water delivery. The location of the Twin Lakes is shown on Figure 1. <br /> <br />The rehabilitation project included breaching the existing dam embankment and replacing the existing <br />corrugated metal discharge pipe with a 30-inch diameter ductile iron pipe bedded in non-reinforced <br />structural concrete. A concrete spillway/outlet structure with a sluice gate and trash racks was <br />constructed to replace the existing outlet structure. A vehicle turnaround was constructed using pit <br />run, riprap bedding, and riprap. The dam crest surrounding the reservoir on the north, south, and east <br />sides were regraded to gauge elevation 12.7 and the west side was regraded to gauge elevation 13.3. <br />The dam crest was covered with three inches of Class 6 road base. The construction items were <br />completed for the Boulder and Left Hand Irrigation Company by Kemp & Hoffman Inc. of Northglenn, <br />Colorado. Rocky Mountain Consultants, Inc. (RMC) provided construction related engineering <br />services. The project construction began in late February 2001, and was substantially completed by <br />early May 2001. Representative construction photographs are included in Appendix A. <br /> <br />1.1 Key Proiect Components <br /> <br />~ Concrete Spillway/Outlet Works Structure: Emergency and service spi II way constructed with <br />two 4-foot by 5-foot vaults with12-inch thick walls, 42-inch diameter RCP at the inlet, and a <br />30-inch by 30-inch Waterman medium-cluty sluice gate. <br /> <br />~ Spillway and Outlet Works Pipe Replacement: Replaced the existing 30-inch diameter <br />corroded, corrugated metal pipe with 74 lineal feet of 30-inch diameter restrained joint ductile <br />iron pipe. <br /> <br />~ Vehicle Turnaround Construction: A 30-foot by 40-foot vehicle turnaround was constructed <br />with imported pit run placed on the upstream side of the dam crest. A six-inch thick granular <br />bedding was placed between the pit run and 18-inch thick riprap layer. <br /> <br />~ Dam Crest Grading and Road Base Placement: The dam crest was graded to gauge elevation <br />12.7 on the north, south, and east sides of the dam. The western dam crest, along the Boulder <br />and White Rock Ditch, was raised to gauge elevation 13.3. Three inches of Class 6 road base <br />was placed on the entire dam crest and the road was graded to provide for drainage toward the <br />reservoir. <br /> <br />FINAL CONSTRUCTION REPORT - Davis No.1 Dam <br />Outlet Works and Spillway Rehabilitation <br /> <br />-1- <br /> <br />May 2001 <br />1:\0057 _059.mjb\Construction ReponIConstruction.rpt.wpd <br />