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08/29%97 09:52 $`1 JOJ 985 2080 GOIDER-GCS ~ fm 001/001 <br />MEMORANDUM <br />TO: Christine Johnston <br />FROM: William Patterson <br />DATE: August 27, 1997 <br />RE: Regpoose To DMG Question 1-August 15, 1997 <br />The Division of Minerals and Geology (DMG) is concerned that culvert CCW-1B is undersized. <br />It was stated that the minimum size of culvert CCW-1B should be 54" rather than 48" due to the <br />additional flow from DSLY-9 entering the culvert system at Manhole iY2. They have supplied a <br />Sedcad culvert analysis to verify this claim. _ _ _ <br />The Sedcad methodology provided by DMG is not applicable to the flow regime expected <br />inculvert CCW-1B. This methodology is only applicable m pottded water at the headwall of a <br />culvert. When culverts operate under inlet control, culvert size is generally dictated by entrance <br />conditions, at the headwall, moving ponded (no velocity) water into the culvert. For the case we <br />are modeling, 127 cfs is already flowing in the 48" diameter pipe with a flow depth of 3.3 feet. <br />The calculation required far design is for a stormwater inlet conveying an additiooa129 cfs into <br />the storm sewer system. <br />At manhole fiZ inlet a flow of approximately 127 cfs is entering the manhole from a 48" diameter <br />culvert at a velocity of 11 fps. Approximately 29 cfs from ditch DSLY-9 is entering this same <br />manhole through a drop inlet. The combined flow of 157 cfs is leaving manhole rfl2 through a <br />48" diameter culvert. The appropriate methodology to calculate the water depdr in the manhole is <br />to consider the momentum of water already in the system, and presstuizadon of the inlet and and <br />outlet pipes neaz the manhole due to pontiing water in the manhole. <br />The estimated depth of the water in manhole J/2 will be approximately 6.5 feet doting the peak of <br />the 100-yeaz, 24-hour storm evem. This depth is about 3 feet below the inlet elevation. The <br />uniform flow depth in the 48" diameter culvert downstream of manhole #2, carrying 158 cfs, is <br />orily 1.6 feet. Accordwgly, a 48" diameter culvert is appropriate for this application. <br />Please contact the with any additional concerns. <br />Sincerely, <br />William Patterson <br />Water Resources Engineer <br />The dacLymem(s) with this ns"~*+%«iw are oNy for tecipiem(s) tamed above and contain privileged/confidemial information. <br />UttauthorizW disclosvrc, dissemination, copying of this transmission it sniNy prohibited. ff received in ertor, please destroy. <br />Questioaslproblems with transmission: Comae ].mda Duff az (303) 980-0540, Facsimile (303) 985-2080. <br />CALDER ASSOCIATES INC. -DENVER OFFICE <br />200 Unim Boulevartl, Suite 500 Lakewood, Colorado USA 802.28 <br />