Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure B-17.—Portable pump used to initiate draining of the reservoir.The initial flow of water through the breach (figures B-18 and B-19) was allowed tostabilize and diminish, and then the process was repeated to remove another smallportion of the embankment dam. The excavation of the embankment material waskept at a minimal amount to limit the quantity of water discharging through thebreach section. This process was repeated, and each time the water flowing throughthe breach was allowed to flow out and stabilize before removing additionalembankment material. The partial breaching of the embankment dam wascompleted over 2 days. The final dimensions of the breach obtained consisted of an8-foot wide bottom, a 65-foot top width, a depth of 20 feet, and side slopes of1.5H:1V. The bottom of the breach section was provided with rock riprap erosionprotection. The embankment dam was not completely breached to allow for a smallreservoir with a depth of 8 feet to remain for the purpose of controlling silt depositsin the reservoir and to maintain a fish habitat. With the partial breaching of theembankment dam, the dam was considered to no longer pose a safety hazard to thegeneral public.Lessons learnedThis event demonstrated that with a relatively small reservoir and small embankmentdam height, the reservoir can be released in a controlled manner by pumping andperforming a controlled breach of the embankment dam. Care should be employedwhen attempting to release the reservoir by means of a controlled breach of theembankment dam.B-20