Technical Manual: Conduits through Embankment Dams (FEMA 484)

Appendix B—Case HistoriesFigure B-16.—Cracking at the embankment dam crest above the sinkholeon the upstream slope of the embankment dam. Note the simple staking ofthe area to monitor movement of the crack.surface level of Balman Reservoir. After five days of diverting the water, the watersurface level in Balman Reservoir was lowered only approximately 1 to 2 inches, andthe reservoir level remained just below the spillway crest. At this rate, the reservoircould not be drawn down in a reasonable period of time and be maintained at a safelevel. Therefore, it was decided to partially breach the embankment dam.On November 15, 1996, a portable 3,000 gal/min pump (figure B-17) was deliveredto the site. The pump was set up adjacent to the spillway and placed into operation.The pump was operated continuously for 3 days, and the water surface level of thereservoir was lowered to approximately 8 feet below the spillway crest. At this point,the excavation to breach the embankment dam was commenced. A Caterpillar 330track-mounted excavator was used to perform the excavation. The area of thesinkhole and the upstream slope were first excavated as far into the reservoir as theexcavator could reach, and then the embankment dam crest was benched downapproximately 4 feet on either side of the breach. The breach was excavated on bothsides at a slope of 1.5H:1V down to the water surface level. Rocks of varying sizeswere placed in the bottom of the excavation and down the downstream slope of theembankment dam to help control erosion. Then, a small amount of theembankment dam was removed from the breach entrance, and water was allowed toflow through the breached section. Some minor slope erosion occurred, but nobackcutting of the channel into the embankment dam was observed.B-19