- Forensic evaluation
- Alternatives evaluation
- Spillway design
- Construction documents
- Resident engineering
- Construction administration services
East Sprat Platte Reservoir is a lined, below-ground water storage reservoir located along the South Platte River in Adams County, Colorado. A spillway is located along the northwest corner of the site to provide controlled filling of the reservoir during flood events in the river. The original spillway (designed by others) consisted of a 300-foot-long, 3-foot-deep, loose placed, riprap lined channel with a concrete cutoff wall near the river. The spillway was engaged twice in consecutive years from flood events in the river and was severely damaged during both events.
RJH conducted a forensic investigation to identify causes for the spillway damage. We identified that the broad spillway crest was not uniformly distributing flow through the spillway but was concentrating flow along the north end of the spillway, which resulted in increased flow velocities and erosion. Also, the spillway chute could not hydraulically contain spillway flows, which resulted in flows spreading from the riprap to the unprotected reservoir slopes.
Following the forensic evaluation, RJH evaluated spillway rehabilitation alternatives for technical and economic feasibility, and developed a final design concept based on these evaluations. RJH evaluated various spillway lining alternatives including conventional concrete, articulated concrete blocks, and grouted riprap using on-site materials. This evaluation showed that the grouted riprap alternative resulted in significant cost savings over other alternatives because the existing riprap could be reused, and Thornton ultimately selected this concept for final design.
RJH performed conceptual through final designs, and provided construction phase services for the project. A year after construction, the spillway was engaged during the 2013 historic flooding in Colorado. RJH and Thornton inspected the spillway following the flood and concluded the spillway performed as expected with no damage.