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<br />Page 3 of letter to <br />Colorado Geological Survey <br />December 8, 1972 <br /> <br />Below the existing county road a much wider channel will be required to carry <br />the flow since the natural gradient changes abruptly to about 2~%. Here the <br />average velocity will drop appreciably. In turn, the flood water will begin to <br />deaos it its load of sediment. If the reach of channel from the road to the ri ver <br />is' relatively short, then the material that remains suspended will, of course, <br />be fed into the Crystal River. Sediment ponds will, therefore, be provided to <br />handle the debris flowage as well as reduce the quantity of suspended material, <br />thus eliminating the possibility of debris flow into the river. <br /> <br />Although other alternates appear feasible, safe development of the lower mud <br />flow area of Slate Creek will require considerable engineering study; more than <br />has been part of the present report. As recommended by Dr. Robinson, in all <br />cases the channel should at least carry the annual flows in the lower reach of <br />Slate Creek. It does not appear economically feasible that a channel can be de- <br />signed to carry the total debris flowage in the lower area if it is assumed that <br />the volume of transported material cannot be reduced up stream. We feel that by <br />stabilizing the upper reaches of Slate Creek, the total volume of transported <br />debris will be appreciably reduced for this lower area. We would suggest staged <br />construction, whereby improvements in the upper reaches could be completed before <br />ruling out any alternate design for the lower area. <br /> <br />Regarding maintenance, it is believed that little maintenance will be required <br />in the upper reaches of Slate Creek. Based on one weeks work for a crawler <br />tractor, or backhoe, per year, this would amount to only $2,000 per annum. How- <br />e;e-, more mai ntenance wi 11 be requi red in the lower reaches of 51 ate Creek to <br />remove materi a 1 from the sediment ponds. Assumi ng that the mud flow 1 ast year <br />was representative, then at one dollar per cubic yard, this would have cost the <br />District an additional $2,500. Summarizing, we feel that once the gradient of <br />Slate Creek has been stabilized, the amount of sediment transported will be re- <br />duced, and so will the cost of maintenance. <br /> <br />C}'~C~': p~u~~' <br /> <br />Jares R. Davi s <br /> <br />JRD: et <br />Att.: Exhibit No. 1 - Storm Hydrograph <br />Exhibit No.2 - Flood Plain Channel <br />Exhibit No.3 - Channeling <br />Copy of Nov. 2nd Letter from Dr. Charles S. Robinson <br />Appendix I - Bibliography <br /> <br />KETCHUM . KONKEL . BARRETT' NICKEL . AUSTIN <br /> <br />