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, RECEIVED June 9, 1995 JUN 1 3'95 INCIDENT REPORT Lake Henry WATER RESOl'RCES STATE ENGIEER QJI.O w, Div, 2, DAMID: 170203 At approximately 2:30 P,M., I was notified by Allen Ringle, Lake Henry Reservoir superintendent, that a large piping condition had been discovered near the north end of the east embankment in which approximately 400 gpm of muddy flow was exiting beyond the toe of the downstream slope into the West Ditch. I arrived at the site at approximately 4:15 P,M, and found the condition to be as described. A piping hole of approximately 18 inches in diameter was visible in the west slope of the West Ditch, approximately 5 feet below the top of the ditch. A second smaller pipe and seep was visible approximately 20 feet to the north. This flow was not nearly as muddy and flow was estimated at 40 to 50 gpm, A captured flow sample in a one gallon bucket from the large pipe was allowed to decant and approximately 1 inch of sediment was visible in the bottom of the bucket. A large crack and saturated slide was visible along the West Ditch, adjacent to the piping location, The reservoir was at gage height 10 feet, which is full, Allen had ceased diverting into the reservoir and had begun releasing at a rate of approximately 125 cfs, the outlet channel capacity, It was determined that at this rate, it would take nearly two weeks to lower the reservoir down to the seepage level, -1-0 In an effort^ slow down the erosive flow which was occurring, a large front end loader with a full bucket of sand was used to roll over and collapse the smaller pipe to the north, A cavern was exposed in which flowing water was clearly visible, Several loader buckets of sand were placed in the cavern and the flow was completely stopped. After the successful attempt on the smaller pipe, the same procedure was used on the larger pipe and by approximately 8:30 P.M., the flow from the large pipe was reduced to less than 1 gpm and flowing clear. It is believed that a sand lens in the embankment cross section is the source of the seepage and piping and that the seepage may have followed a rodent hole into the West Ditch. The reservoir will continue to be drawn down to gage height 7 feet and the possibility of using sheet piling to cut off the seepage flow from the sand lens is currently being evaluated by the owner's engineer, Robert M, Robler. The owner will continue to monitor the condition closely. Michael L. Graber Division 2 Dam Safety Engineer xc: Alan Pearson, Allen Ringle, Don Taylor