Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure B-37.—Erosion scarp on downstream slope of the embankment damat the location of the overtopping of the dam crest.channel widens significantly. The dam break flood would attenuate rapidly at thispoint; however, the flood would still pose a threat to the one home and anyonefishing and hiking in or along the stream channel. With the long Independence Dayweekend approaching, it was anticipated that heavy recreational use in the area couldbe expected, and the embankment dam in its present condition posed a real threat tothe safety of the general public.Several futile attempts were made to operate the outlet works. Since the outletworks was inoperable, it was decided to perform a controlled breach of theembankment dam down to a safe level. After some discussion concerning therelative difficulty in getting heavy equipment to the damsite, and the significantenvironmental damage that would ensue, it was suggested that it would not take allthat much effort to perform a controlled breach using manual labor. Prison inmateshad been used previously to perform routine maintenance on embankment dams,such as tree and brush removal. A phone call late in the afternoon to the BuenaVista Correctional Facility found them willing to provide eight young men, equippedwith picks and shovels the following morning.After the inmates and a guard were transported to near the damsite via four-wheeldrive vehicles, a plan was devised and explained to the inmates. Breach excavationwould start at the downstream toe, and slope gently upward to within 1 foot of theupstream slope. The excavated breach would be lined with rock, which had to beB-42