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<br />Lawn Lake, OC-39 <br />July 15, 1982 <br /> <br />Page 7 <br /> <br />a. The downstream portion of the outlet pipe had I:ccn wil~hcd aWilY filr downsLream <br />from the dam ~it'-'. (The down~trcuJ~ort,on of Lhe outlet conduit wa,; not seen <br />from the air or during the site inspection.) <br /> <br />b. The outlet control valve has been washed free from the upstream end of the pipe <br />and deposited in the eroded channel approximately 200 feet downstream. <br /> <br />c. The upstream portion of the outlet conduit remained embedded in the foundation. <br />(See photo 2" photo sequence 14 through 17, and photo 94,). This pipe was <br />partially sumerged during inspection and could not be closely observed. Cursory <br />inspection indicated the pipe was in good condition. <br /> <br />8. Rodent Damaqe. <br /> <br />Two large rodent holes were found In the crest of the dam at approximately station <br />1+75. (See photo 100.) These rodent holes had a diameter of about six inches and <br />appeared to have been caused by bager or marmot activity. <br /> <br />Remarks -- The follOWing photographs were taken by John VanSciver: <br /> <br />#'59,10,11. and 12 -- Emergency spillway. <br /># 13 -- Forked pine tree at right abutment at station 5+18. <br /># 14 through 17 -- Panorama of the breach as viewed from the upstream side. <br />#18 -- Right side of breach showing location of organic and sand seams. <br />#19 -- Ocganic seam running through dam 5 feN below crest. <br />#20 -- Clean, coacse sand lense 10 feet below crest of dam. <br />#21 -- Organic peat layer with tree roots, approximately 12 feet below crest of dam. <br /># 22 -- Left side of breach showing continuation of organlc layer. <br />#23 and 24 -- Sand plume deposited on bench downstream of breach to the right of the <br />channel. <br />if 1 Suspected seepage area on downsrream slope 60 feet to the right of the breach <br />and 5 feet 7 inches below crest of dam, <br /># 2 Close-up of the left side of the creach showing organic layer. <br /># 3 Right side of eroded channel showing breach and foundation exposure. <br />#'54,5, & 6 -- Panorama of breach as viewed from downstream. <br />#' 5 7 & 8 -- Sand plume on left 5 ide of eroded channel approximately 50 feet <br />downstream from the dam. Note: Outlet villve in channel. <br />if 9a -- Rema ins of outlet conduit. <br /># lOa -- Rodent holes in dam at approximate ly station 1 + 75. <br /> <br />Discussion -- The follOWing discussion is relevant to the failure of Lawn Lake and to <br />Cascade Dam. <br /> <br />1. At 1:00 P. M., we met with Roger Patterson of the 13ureau of Reclamation. Roger <br />had ceen photogcaphing the drainage area i:elow Lawn Lake as well as the dam <br />site itself. He said he had good photographic coverage and offered his assistance <br />In this way. <br />