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PacifiCorp, Yale Dam Bull Trout Reduction Entrainment Project

Design-Build Project — 2009 ACEC of Idaho Engineering Excellence Award, First Place

McMillen was retained to design and install a net system in Yale Lake to reduce entrainment of bull trout at the intake. A study to evaluate entrainment reduction methods has been completed and resulted in a decision to construct a net across the reservoir in front of the intake with location dependent upon velocity flows and netting size. The proposed net will be fabricated from Dyneema, which provides a higher strength net and a lower net profile than many comparable net materials. Dyneema nets can withstand higher velocities and for the same strength are 1/10 the size of a comparable nylon product. Though Dyneema is a more expensive product than nylon net material, the higher strength and durability will provide PacifiCorp with the best value and lowest life cycle costs.

McMillen worked closely with PacifiCorp throughout the permitting phases starting with the permitting strategy memorandum. This memorandum outlined the regulatory entities which must approve the project, identify and obtain the permit forms, and outline a step-by-step process and schedule for obtaining the required permits. McMillen prepared the permit applications and assisted PacifiCorp with responding to questions from the regulatory agencies. The design drawings and preliminary engineering reports provided the required data and illustrations for support preparation of the permitting documents. McMillen’s in-house environmental and permitting staff were responsible for the permitting work activities. All permitting activities were conducted concurrently in order to ensure full project approval prior to mobilization to the project site.

McMillen’s Construction Division installed the dam face anchor and embankment anchor prior to delivery of the entrainment net. PacifiCorp had a scheduled outage of the powerplant for routine maintenance which would allow for no flows through the intake. This set the schedule for the installation of the net into the reservoir providing PacifiCorp no loss power generation during construction. McMillen installed a wooded ramp off the face of the dam which would enable net installation from the upper dam road. The net was bound upon delivery which would keep the netting coiled during attachment of all anchor points. Once the net was anchored the binding was released allowing the netting to curtain fall to the bottom of the reservoir. Guide lines had been stitched into the net to allow the dive team to install the additional concrete anchors. A floating modular barge was used to drop 4000lb concrete anchors to the bottom of the net attaching to the bottom anchor chain. Due to the organization of all field crews McMillen was able to decrease the secluded install of the net system from ten days to three, saving the client money and loss power generation. Once the net was installed McMillen added 2-12” HDPE floats for additional flotation through the main center section of the net system.