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Design Report <br /> Goose Haven Reservoir Cell 2A <br /> May 14, 2021 <br /> Page 3 of 7 <br /> 2.4 Diversion Swale <br /> An diversion swale will collect surface runoff water from land south and west of Cell 2A and route <br /> the water around the reservoir to a discharge point northwest of the reservoir footprint. The sizing <br /> of the diversion swale is discussed in Section 7.6 of the Project Breach Inundation Mapping <br /> Report; the diversion swale is referred to as a perimeter channel in that report. <br /> 3 SITE REQUIREMENTS <br /> The Cell 2A site and the vicinity do not contain significant improvements that require special <br /> consideration for design and construction of the reservoir. Much of Cell 2A has been in operation <br /> as a gravel pit, therefore much of the excavation for the embankment already occurred and <br /> dewatering infrastructure is already operating. <br /> Several homes are present to the west of the Cell 2A site and are within the jurisdiction of <br /> Unincorporated Boulder County. The designed diversion swale on the western side of Cell 2A <br /> adheres to setback requirements of Boulder County. <br /> The property north of Cell 2A is currently an open field owned by Boulder County. The diversion <br /> swale discharges into this property. The dam breach analysis presented in the Project Breach <br /> Inundation Mapping Report models the dam break occurring on the northern embankment and <br /> flowing across the property north of Cell 2A. <br /> The outlet pipe from Cell 2A toward Cell 2 to the east is planned with an invert elevation of 5,024.0 <br /> ft at the Cell 2A outlet and 5,,023.4 ft at the Cell 2 inlet. <br /> Approximately 80 ft of the outlet pipe will be installed in a deep trench in the embankment of Cell <br /> 2. Approximately 160 ft of the outlet pipe will be installed using trenchless techniques to avoid a <br /> deep trench excavation below an existing 36-inch water main. Neither Cell 2A or Cell 2 are <br /> currently holding water for storage, and we understand that construction of Cell 2 is not complete. <br /> Specification Section 31 71 10 requires that both Cell 2A and Cell 2 are drained below the <br /> trenchless casing pipe invert elevation while the trenchless casing pipe is installed. <br /> The properties south of Cell 2A are currently open fields or are in use for agriculture. Aside from <br /> stormwater runoff considerations from these properties, we do not regard them as having a <br /> significant effect on the design or construction of Cell 2A. <br /> 4 HAZARD CLASSIFICATION <br /> A Low Hazard dam classification is appropriate for the dam as discussed in Section 5 of the <br /> Project Breach Inundation Mapping Report. <br /> BRIERLEY <br /> ASSOCIATES <br /> Creating Space Underground <br />