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<br />width of 83 feet. Approximately 6,500 cubic yards of earth were <br />eroded from the embankment section during the event. <br /> <br />The first attempts to close the gap were made about 3:30 p.m. <br />on Sunday afternoon, when the breach was approximately 75 feet <br />wide. A bulldozer, working on both sides of the breach, <br />constructed a dike into the reservoir where flow velocities were <br />minimal. However, it was not until 9:15 a.m. on the following <br />morning (Monday) that the gap was finally closed. <br /> <br />Within this approximately 24-hour period, the water level fell <br />from an initial gage rod reading of 36 feet to 27 feet, a total <br />drop of 9 feet. This represents a loss of approximately 2,880 <br />acre-feet of water, about half the reservoir's contents. <br /> <br />The relatively small channel below Prospect Valley Reservoir <br />was inundated as the flood progressed toward the confluence with <br />Lost Creek. A study of arrival time versus distance, as reported <br />by various observers in the path of the flood, shows that the velo- <br />city of the flood front in this 6-mile reach above Lord Reservoir <br />averaged 1.4 miles per hour (2.0 feet per second). The width of <br />the flood below the reservoir ranged from about 1,000 to 1,500 <br />feet. <br /> <br />Upon entering Lost Creek, the flood was confined to the <br />better defined channel until it reached State Highway 52. The <br />flood width in this reach was narrower, ranging from 200 to 400 <br />feet. State Highway 52, acting as a barrier upstream of Lord <br />Reservoir, spread the flood to a width of approximatly 3,200 feet. <br /> <br />Before the flood, Lord Reservoir, at its maximum allowable <br />capacity had a gage reading of 10.3 feet and contained approxi- <br />mately 1,280 acre-feet, about 88 percent of its unrestricted <br />capacity. The water level was 2.0 feet below the level of the <br />emergency spillway on the right abutment, and 0.7 feet below a <br />smaller concrete service spillway located near the center of the <br />dam. <br /> <br />FIG.5 <br /> <br />FLOOD HYDROGRAPHS <br /> <br />4000 <br /> <br /> , <br /> 1 , 1 <br /> I I , <br /> , , <br /> TO; <br /> 'W.ir <br /> , IL <br /> I -:; <br /> T I" <br /> 1- <br /> .. ,...1., ,; <br /> ~v <br /> ,. /0, <br /> , ! <br /> III l' <br />I i I 1 I i I I ; i I <br /> 9 12 3 6 9 12 3 6 9 12 3 6 9 12 3 6 9 <br /> SUN DAY 2- 10- 80 1 MONDAY 2-11-80 I TUESDAY <br /> <br /> 3000 <br />- <br />(f) <br />I.L <br />U <br />- <br /> 2000 <br />Q) <br />E' <br />c <br />.c <br />0 <br />CI) <br />b 1000 <br /> <br />o <br /> <br />Time in Hours <br /> <br />5 <br />