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<br />,. <br /> <br />Lawn Lake, OC-39 <br />July 15, 1982 <br /> <br />Page 10 <br /> <br />Survey the emer;ency spillway control section as well as the centerline section <br />of the spillway. <br /> <br />These function,; coulu ue perrormeu I,y il t<Cilm or two inuiviuuill,; u,;iny lOO-foot <br />tape and hand-level. <br /> <br />c. Perform a close inspection of the rema ins of the outlet system. Inspect the <br />remaining upstream portion of outlet conduit for signs of damage that may have <br />indicated piping into the embankment. <br /> <br />Inspect the outlet control valve which ls currently located 200 feet downstream <br />of the dam. Confirm that the valve was closed at the time the dam failed and <br />look for signs of damage which may have indicated piping into the embankment. <br /> <br />Attempt to find the downstream section of outlet conduit either by foot or by <br />aerial reconnaissance. If found, this downstream portion of the conduit should <br />be inspected in an effort to determine its condition prior to fallure. <br /> <br />d. Excavate the downstceam slope at the two suspected seepage locations <br />60 and 120 feet to the right of the right s ide of the breach. Remove the over- <br />bucden and provide a geotechnical description, with photographs and samples, <br />of the exposed surface of the embankment. This work will require considerable <br />excavation and should be performed by a teain of two persons in conjunction with <br />an Individual from our geotechnical branch. <br /> <br />e. Excavate the crest of the dam at approximately station 1+75, and elsewhere, where <br />rodent holes are observed. Attempt to determine the depth of rodent aC'ivity and <br />map the course of the rodent passage-ways. This function will eequire considerable <br />excavation and should be done by a team of two persons in conjunction with a <br />member of our geotechnical branch. Photographs, samples, and geotechnica! <br />mapping may be required. <br /> <br />f. Carefully inspect the upstream slope of the dam and spillway channel to find <br />high water marks which may be useful to establish water surface elevation at <br />the time the dam failed. In conjunction with this, estimate the amount of water <br />flOWing currently through the breach by measuring cross-sectional area of flow <br />and estimating velocity. (Th is latter piece of information will be useful in <br />determining depth of flow through the emergency spillway at time of failure.) <br /> <br />2. Follow-up Enoineerino: <br /> <br />a. Perform soils tests on samples obtained during stage 2 data gathering. These <br />tests should include solI classification, soil dens ity, solI moisture content, <br />and permeability. (Further tests may be required to satisfy studies as outlined <br />below). <br /> <br />b. Perform a stability study of the embankment using the obtained cross-secticnal <br />