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­Q� COLORADO LEGACY LAND <br /> ECHNICAL REVISION#28,COMMENT AND RESPONSE SUMMARY TABLE <br /> RESPONSE TO COMMENT <br /> conveyance structure for runoff from this 4.1-acre area,pursuant to <br /> Rule 7.3.1(3).Please provide these analyses and designs. <br /> Letter-Hydraulic Design. a) The new design is utilizing a ditch instead of a pipe. The <br /> ditch allows for a greater cross-sectional flow area, can be <br /> -Additional clarification is required. installed on a curve (thus avoiding manholes and sharp <br /> a. The response indicates the system is designed to operate bends),makes collecting water at the upstream end easier,and <br /> under open channel conditions,yet the majority of the30- allows the addition of lateral flow along the alignment. <br /> inch pipe alignment on Sheet 4 shows the hydraulic grade <br /> line above the top of pipe and the energy grade line as high Table 1 shows the hydraulics associated with the minimum <br /> as 30feet above the pipe invert at the manholes.This result and maximum slopes for the two design flows expected in the <br /> indicates the system will operate mostly under pressure ditch during a 100-year runoff event. <br /> flow.Furthermore,it is somewhat counterintuitive the <br /> hydraulic grade line for the 30-inch pipe indicates the flow is <br /> open channel immediately downgradient of the upper and <br /> middle manholes,transitioning to pressure flow as flow <br /> approaches the downgradient manhole,with an <br /> approximate five-foot hydraulic grade line drop across these <br /> manholes.Entrance and exit losses typically result in higher <br /> hydraulic gradients at manholes.The opposite appears to be <br /> 4 the case at the lower manhole,where the pipe gradient is <br /> flatter(again counterintuitive)with open channel flow <br /> entering the manhole(at STA 5+26.55).Please explain how <br /> the system is designed to operate under open channel flow <br /> conditions when it is mostly pressure flow conditions and <br /> explain the unusual hydraulic performance. <br /> b. Given the apparent high pressure at the upper and middle b) No longer applicable. <br /> manholes,the Division is concerned about the reliability and <br /> safety of the bolted lids at the manholes as well as the likely <br /> possibility of high-pressure leaks developing at pipe joints, <br /> potentially forcing unknown amounts of water into the <br /> NWRP in a similar fashion to observed failures in municipal <br /> water supply lines under city streets.This particular design <br /> is contrary to Rules 3.1.5(10)and(11),6.4.21(6)and(10), <br /> and7.3.1(3).Please address the concerns related to safety of <br /> the manhole covers and the potential for water to enter the <br /> NWRP through pressure leaks at the pipe joints. <br /> PAGE 3 OF 10 <br />