Wasteway No. 5 Reregulation Reservoir

CLIENT Roza Irrigation District

Location Sunnyside, WA

Shannon & Wilson was part of the design team to perform an in-depth feasibility and design study for a 1,600 acre-foot, reregulating reservoir north of Sunnyside in Washout Canyon for the Roza Irrigation District.

Shannon & Wilson performed initial feasibility geotechnical engineering services to identify cost-effective embankment and reservoir alternatives that are also feasible from an engineering standpoint.  Our initial work involved reviewing existing geotechnical information, regional geology and seismic information, and well logs.  We performed limit equilibrium embankment stability calculations to evaluate the preferred alternatives, and provided data and analysis to evaluate materials for use as dam shell, filters, drains, and liners.  The configurations included estimated embankment slope inclinations and embankment zones, including core and drains.  We assisted the design team to generate geologic profiles for use in estimating material quantities required for embankment construction and developed a detailed scope for field investigation and engineering analyses tailored to the preferred alternative.

In 2011, Shannon & Wilson conducted the Phase I field exploration which included mud-rotary borings, sonic core borings, test pits, and a downhole geophysical survey.  The subsurface information was used to further evaluate and refine the reservoir design.  The evaluation included seepage and slope stability evaluations, embankment settlement evaluation, filter design criteria, and seismic stability and deformation evaluation.  We drilled additional explorations in 2013 to further evaluate the subsurface conditions to address issues identified during the design process.  Preliminary site grading and moisture conditioning occurred in late 2013, with mass grading in 2014 and 2015.  Spillway, pump station, and liner construction started in 2016.  The reservoir was completed in the Fall of 2017.


Stan Boyle
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