West Reservoir No. 1

Challenges

West Reservoir No. 1 dam is a 35-foot-tall homogenous earthen embankment dam located in Delta County, Colorado.  A zero-storage restriction had been imposed by the Colorado Office of the State Engineer (SEO) because of severe deterioration of the outlet works pipe.  A previous investigation by the SEO found rust holes, missing portions of the pipe invert, and voids along the outside of the pipe.  Collectively, these issues created unsafe circumstances for normal reservoir drawdown.

Solution

Rehabilitation included the full removal of the existing outlet works conduit and intake and outlet structures, which involved excavating the existing embankment.  Once removed, new facilities were constructed that included a reinforced concrete-encased HDPE outlet works conduit, a new intake structure and slide gate, and an end wall and energy dissipation structure.  The embankment was then replaced with fill and reinforced with upstream slope protection.

RJH oversaw the rehabilitation from analyses and design through the construction phase.  Various analyses included hydraulic studies to size the new outlet works conduit, vent pipe, and rating curve; filter compatibility design to manage the seepage along the new outlet works conduit; geotechnical and structural evaluations to design the intake structure and stilling basin; and wave run-up analyses to design riprap and riprap bedding slope protection.