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i, <br />Page 3 <br />Mike Savage <br />December 19, 1980 <br />The applicant should be aware that haul road culverts must be designed to <br />pass a 10 year 24 hour storm without a head of water at the inlet. If a head <br />is needed then the embankment must be protected from erosion and fill saturation. <br />This is usually accomplished by a rock or concrete head wall. Specifications <br />on design headwater and headwall protection methods, must be supplied for our <br />review. <br />I checked the design of Culvert C-1 making some assumptions to get an idea <br />of how well your designs are. If I assume that culvert C-1 is CMP, inlet <br />controlled, and projecting, the design Nw = 6 feet. This would mean that the <br />design headwater would br. 12 feet. D with these assumptions it appears <br />that culverts were designed with no consideration of the design headwater. <br />It appears that most if not all culverts, are underdesigned and will have to <br />be redesigned properly to get our approval. <br />Ditch Designs <br />Peak dischrage calculations for ditches 22-D1, 22-D2, 22-D3, and the Pit #l <br />collection ditch are incorrect because the equivalent area compensation factor <br />was not considered. This is the same problem that was noted in my December 5, <br />1980 memo explained in comment k7. Revised peak dischrage calculations must <br />be submitted. <br />These ditch designs should also include information on the size and type of <br />rock used to line the ditches. Also, it should be indicated whether this <br />rock will Line the entire stretch of the ditches. If rock will not Iine the <br />entire ditch then the applicant must indicate what the lining will be (type <br />of vegetation, type of soil, etc.). <br />Pond Designs <br />Peak discharge calculations are incorrect for pond sizing. Revised peak <br />discharges and pond storage designs must be submitted. (See comments b7 and <br />#8 of my December 5, 1980 memo to Mike Savage). Emergency spillways will also <br />have to be redesigned. Ponds with embankments greater than 10 feet (from the <br />toe of stream to the crest of the emergency spillway must be approved by the <br />State Engineer's office. We will need documentation that this was done. <br />IF TBM wants approval of manually operated pond dewatering devises, they <br />must explain how the 3" plastic pipe will be opened when mining is completed <br />and personnel are not present at the mine site. This type of dewatering device <br />requires continual maintenance to open the pipe after storms and is subject to <br />clogging with sediment. TBM must either submit a plan for continual maintenance <br />