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<br />, 'Oct-31-Z00Z 11 :33am From- <br /> <br />T-599 P.007/00B F-97Z <br /> <br />Mr. Jim Norfleet, P.E. <br />Mr, Jack Byers, P.E. <br />Page 6 <br /> <br />July 11, 2002 <br /> <br />outflow is estimated at 20 cfs! The service spillway conveys 35 cfs before the lake <br />level reaches the overflow spillway, , <br /> <br />Service Spillway. The existing 36 inch CMP service spillway Is approximately 40 years <br />old and has leakage around the pipe. The spillway pipe will be removed and replaced <br />with a new 36 inch smooth interior wall pipe. It Is proposed to use ADS N.12 HDPE <br />pipe with neoprene gasketed water tight Joints. This pipe requires a minimum 1 foot <br />of cover for H-20 loading. ,More than 2 foot of cover will be provided under driving <br />surfaces. A pre cast concrete head wall with inclined trash grate will be installed at'the <br />spillway Inlet. The spillway pipeline extends beyond the new embankment and outfalls <br />on the channel side slope in a rock rip rap lined channel, The channel rip rap has a Qo <br />=- 24 Inches and is laid on a bedding consisting of 6 inches of graded granular filter <br />material and a geotextile fabric. <br /> <br />The service spillway has a capacity of approximately 70 cfs at the dam crest. The <br />balance of flood flows would be conveyed through the existing swale ("overflow <br />spillway") in the east abutment. <br /> <br />Overflow Spillway <br /> <br />The existing overflow spillway capacity will not be altered by this project. The capacity <br />of the overflow spillway was estimated using a critical cross section at the "crest" of <br />the spillway. The spillway crest was located by surveying elevations along the <br />overflow path. A rating table was developed based on critical depth through the cross <br />section for various flows. The calculated capacity of the overflow spillway is <br />approximately 926 ef8. <br /> <br />The current configuration of the dam and overflow spillway can convey the 0.76 PMP <br />flood flow around the dam with essentially no freeboard. The flood flow may result in <br />shallow flooding around a cabin on the Alexander Lak~ Lodge property. New criteria <br />for estimating the PMP for high elevations is currently being developed. Although there <br />may be cost savings associated with spillway improvements at this time, it would not <br />be prudent to spend additional money until the new PMP criteria Is Implemented. <br /> <br />PROJECT COST u ~o.\~ '''/~II"z. <br /> <br />The englneer~ opinion of probable cost is approximately $~ The cost will be <br />shared between Surface Creek Ditch and Reservoir Company, Delta County and the US <br />Forest Service. <br /> <br />11==1 C l= C n I I C r 1= <br />