The Naches-Selah Irrigation District is an 11,000-acre irrigation district located in northern Yakima County, Wash., and serves over 1,700 landowners. This project involved replacing the existing wood flume and concrete facilities, which were built between 1920 and 1956.
The project began with the demolition of 4,600 feet of existing wood canal flume, which extended over eight massive wood flume trestles as high as 50 feet above the County road and canyon, and the demolition of 2,260 feet of existing concrete canal. These structures were replaced with 3,894 feet of concrete canal and 3,626 feet of 96-inch centrifugally cast, fiberglass-reinforced, polymer mortar (CCFRPM) pipe. The concrete canal sections include a welded polyethylene lining installed under the reinforced concrete canal. The first section of constructed concrete canal required supply trucks to back up 1,200 feet on a 12-foot-wide access road with a steep embankment on one side and the new canal on the other side. Large concrete transition and inlet/outlet structures were built to extend from the 96-inch pipe to the concrete canal sections.
The 96-inch pipe was installed on steep grades, sometimes more than 50%, and the existing access roads had to be widened in order to get the pipe to where it would be installed. Sections of pipe trench excavation were slowed by existing sandstone. Handling the large pipe was a challenge in itself and this was made more difficult given the steep terrain and narrow access roads. Because of the limited access, simply delivering each piece of pipe to an installation point could take as much as 30 minutes. All 185 of the 96-inch pipe joints were hydrostatically tested.
Tapani crews began construction in November and finished the canal and pipework before the water started flowing April 1, when the growing season begins. This project had a very tight schedule in order to get the supply water flowing to local farms. Tapani Inc. crews faced the challenges of a limited number of days, tough excavation, limited site access, and winter construction. During the watering season, any disruption could be damaging to the crops. The overall project had a final construction cost of $6,125,830.