FYRA Engineering was contracted to address the principal spillway rehabilitation needs of ten aging dams in the Upper Salt Creek Watershed. The Lower Platte South Natural Resources District (LPSNRD) in Lincoln, Nebraska, owns and operates numerous grade control dams, and had identified ten sites where the condition of the principal spillway pipe and riser needed immediate attention. A preliminary design report was completed to determine the most favorable solution at each site. This report assessed alternative materials and construction methods that could be used outside the traditional approach, as well as the environmental impacts and improvement options. It was determined that HDPE pipe would be used instead of the conventional corrugated metal piping for the principal spillway pipe and riser. The LPSNRD was also interested in testing the sliplining method of installation. Three dams were identified as test sites for sliplining, with the remaining seven sites utilizing the conventional cut and cover construction method to replace the spillway pipe and riser entirely.

The design and permitting of all ten sites was led by FYRA Engineering. This included performing hydraulic analyses of the structures with HDPE piping, and coordinating with the Nebraska Department of Natural Resources and the Natural Resources Conservation Service to ensure all necessary guidance and design requirements were met. Typical design concepts for each construction method and site specific design layouts were developed and included in two sets of construction plans and specifications (one set for each construction method). The cut and cover sites required quantification of material to be excavated and placed, as well as the materials required for placement of HDPE pipe and riser installation. The sliplining sites required extra attention in the specifications regarding acceptable installation procedures and technology. All quantities were tabulated for construction bidding and cost estimating, and bid documents were assembled. USACE 404 Nationwide Permit and National Pollutant Discharge Elimination System Permits were applied for and obtained for all the sites. Construction management was performed by FYRA Engineering, which included on-site observation, construction reporting and documentation, processing pay requests and change orders, and coordinating with the contractor and client to ensure the project was implemented as designed.