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The Farnsworth Collection Ditch will easily handle the base flow from the adjudicated spring and <br />the highest flow from the pumping operation. The ditch is a minimum of 5' high, 1.SH:1 V <br />sideslopes, minimum bottom width of 2.5', with somewhat vegetated bottom and sides. The slope of <br />the channel is approximately 0.55%. Using a maximum base flow of 0.6 cfs (from Farnsworth), and <br />a Manning's n of 0.025, flow capacity to a height of 5 feet is 400 cfs, from Manning's equation. <br />Since the maximum pumping is 2000 gallons pet minute, this is equivalent to a flow of 4,45 cfs, <br />therefore, the ditch is more than adequate to hold the total flow. The Ditch crosses 4005 Lane in a <br />18" CMP with 4' of head above the culvert to the edge of the road. The total flow must pass through <br />this culvert. The headwater to depth ratio used is 3.0, which is conservative, since the actual ratio is <br />5.5/1.5 = 3.6'7. The maximum flow under these conditions is 18 cfs, which is still considerably more <br />than the design flow of 4.45 + 0.6 = 5.05 cfs. Therefore, the ditch and culvert combination is ade- <br />quate. It should be noted that the culvert is approximately 40% plugged in the pre-mine condition <br />and must be cleaned prior to startup. <br />The U.S. Army Corps of Engineers was also contacted for approval on two items related to this per- <br />mit: First, United wanted the Corps to evaluate the design in the permit regarding the river crossing. <br />Second, the wetlands which would be disturbed and mitigated were studied as part of the COE per- <br />mit. <br />North Fork Pit Mazch 04 21 <br />