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%~ <br />DATE: April 6, 1992 ~~' <br />TO: Janet Hinns ~~~~'` <br />FROM: Steve Wathen <br />RE: C-81-041, TR13 <br />Hydrologic Evaluation <br />Kent Gorham reviewed Roadside's revision for reclamation of their <br />North Decline. The following concerns were encountered: <br />1. On page WW-27, we do not agree with the Mannings Number <br />used (N = .014). Barfield, Warner and Haan lists values <br />for corrugated steel culvert of between .021 to .028 with <br />a median of .024. Please ask them to explain their use <br />of .014. <br />At this point, the operator proposes using one-half of an <br />18 inch culvert for the emergency spillway. With a <br />Mannings value of .024, we would expect a culvert of <br />plus or minus 30 inches in diameter. <br />2. The operator may not be aware that there needs to be one <br />foot of freeboard between peak water level for the 25 <br />year event and the top of the embankment. Please make <br />the operator aware of this. <br />The use of a larger rather than smaller culvert would <br />lower water level to some degree thus incrementally <br />increasing freeboard distance. At any rate, this <br />regulation needs to be taken into account in calculating <br />the secondary spillway or embankment design. <br />3. In order for us to comply with our regulations for Small <br />Area Exemptions (SAE), we must believe that effluent <br />standards will not be exceeded. We do not object to the <br />use of a silt fence in this situation but the operator <br />must be aware that this is a high maintenance item with <br />a relatively short lifespan. Replacement of the fence in <br />the future will require special care to avoid loss of <br />sediment outside the SAE; for which the operator is <br />responsible. <br />In addition, silt fences vary in their specifications. <br />It is important that the operator work with his supplier <br />to obtain the correct fence material for the given site, <br />taking into consideration: runoff area, the soil particle <br />sizes expected at the fence and expected volume of <br />runoff. In order for us to make our determination we <br />need to feel that the fences used have been properly <br />sized, installed and will be properly maintained. <br />