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HYDRO27041
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HYDRO27041
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Last modified
8/24/2016 8:46:27 PM
Creation date
11/20/2007 7:29:20 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980005
IBM Index Class Name
Hydrology
Doc Date
3/11/1991
Doc Name
MEMO MEETING AND SITE INVESTIGATION SEDIMENTATION CONTROL DAM 006 SENECA II HAYDEN ROUT CNTY COLO
From
US DEPT OF LABOR
To
COAL MINE SAFETY AND HEALTH
Permit Index Doc Type
CORRESPONDENCE
Media Type
D
Archive
No
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2 <br />approximately 30 acre-feet from the heel to the spillway crest and the height is about <br />20.5 feet. <br />The Company was kind enough to FAX the March 1, 1991, memorandum to their <br />Flagstaff, Arizona, technical support office for evaluation during the course of the <br />meeting. During a subsequent telephone conversation with Peabody Senior Engineer, <br />Ronald J. Gehrke, Mr. Gehrke, conceded that the original ground upstream toe <br />elevation could possibly be 7062 where the embankment crosses the stream channel. <br />Furthermore, the impounded volume probably exceeds 20 acre-feet. Under these <br />circumstances, the company has two options. They can either lower the open channel <br />crest elevation to approximately 7070 from 7072.5 or bring the facility into compliance <br />and provide the required documentation to permit the dam. This decision is pending by <br />management authority above the engineering department. <br />INVESTIGATION: <br />In addition to the meeting, the author briefly examined the dam and appurtenant <br />structures. The cursory examination of the facility found the following. <br />1. The 24-inch corrugated metal pipe (CMP) principal spillway outlet is simply a <br />culvert with an inlet elevation of 7065.2 and an outlet of 7061.6. The calculated <br />gradient is 2.4 percent which implies that the slope is steep and that inlet controls. As <br />such, pressure flow is considered unlikely. A suitably sized, cubically shaped grid type <br />trashrack was placed at the inlet. Mr. McCulloh was informed that trashracks typically <br />exhibit available area approximately five times that of the inlet barrel area and should <br />be represented on the submitted drawings. In addition, Company personnel were <br />informed that the outlet conduit appeared to be lock-seam corrugated pipe which is <br />prone to exfiltration under very low heads. <br />Normally, lock-seam CMP pipe is not suitable for dam construction where the outlet is <br />expected to operate under pressure. Welded seam corrugated metal pipe is <br />recommended for pressure applications where the designer prefers corrugated metal <br />pipe. Further, watertight bands with O-ring gaskets should be used to preclude <br />infiltration and exfiltration. <br />2. The open channel may be properly designed but it is not properly constructed. The <br />channel shape should be well defined; the riprap lining should be smooth and free of <br />voids with all interstices filled; and the material utilized should be well graded and <br />exhibit a good variety of rock sizes. The channel examined did not exhibit any of the <br />foregoing qualities. In addition, the stone should be strong, durable, blocky material <br />&ee of thin elongated pieces. <br />Should the Company desire to permit the facility under 77.216, engineering calculations <br />will be required to support the design selected. <br />
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