DMAD Reservoir

Ames constructed a 294-foot-wide labyrinth weir concrete spillway, the first of its kind in Utah, at the DMAD Reservoir in Delta. The project was completed nine months ahead of schedule.

The previous spillway no longer met Utah’s Probable Maximum Flood (PMF) criteria, while the new spillway is designed to have the hydraulic capacity to pass the PMF of all upstream floodwaters that feed into the Sevier River Basin. The labyrinth walls feature 17 turns with a radius at the top of the upstream side that allows the water to slowly rise to the top before cresting the structure.

Work scope included demolishing the existing concrete spillway and over-excavating under and around the new spillway structure footprint. The old spillway was built on liquefiable sands, meaning that in a seismic event, the foundation soil underneath the spillway was susceptible to liquefying and failing the spillway. After excavation, Ames replaced the unstable material with stronger engineered structural base course and recompacted embankment material.

The spillway contains more than 6,000 cubic yards of structural concrete. Additional work included dewatering, backfilling, riprap, slope protection rock, spillway channel rock fill, grouting the new wells and sumps, all concrete footing, batter walls, baffles, end sills, chute piers, rebar, three cast-in-place weir boxes, and the bottom and slope slabs of the spillway.