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i <br />MEMORANDUM <br />TO: Job File 477EFC01 <br />FROM: Les Botham <br />DATE: June 30, 1980 <br /> SUBJECT: OSM Regulations and Sedimentation Pond Embankment <br /> _ <br />Heights. ~ <br /> In a telephone conversation with Jeff Saunders of EFC <br /> regarding the language in Section 816.46 (i), we came to <br /> wonder whether the sedimentation ponds designed by LRCWE <br /> were in fact too high. The regulation reads: "An appropriate <br /> combination of principal and emergency spillways shall be <br /> provided to safely discharge the runoff from a 25-year, <br /> 24-hour precipitation event, or larger event specified by <br />• the regulatory authority. The elevation of the crest of <br /> the emergency spillway shall be a minimum of one foot above <br /> the crest of the principal spillway. Emergency spillway <br /> grades and allowable velocity shall be approved by the <br /> regulatory authority." The question is where the crest <br /> ~ <br /> of the spillway is. In the LRCWE design, it was assumed <br /> that the crest was at the top of the riser. The attached <br /> sketch shows the riser-type spillways designed by LRCwE. <br /> One foot of elevation was added to the top of the riser <br /> elevation to get the elevation up the emergency spillway. <br /> In the telephone discussion with Jeff Saunders, I <br /> envisioned_a different kind of a riser, which would consist <br /> of a small pine in diameter similar to the holes designed in <br /> our risers. The top of the riser would be at the sedimenta- <br /> tion elevation. In this case, the pounding head for the <br /> ten-year, 24-hour storm inflow would generally be greater than <br /> one foot so the elevation of the emergency spillway could be <br />. at or just above the elevation of the routed ten-year flow. <br />Leonard Rice Consulting Waler Engineers.lnc. <br />