Water Resources Division Wins Morony Dam Spillway Gate Design-Build Project

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McMillen Jacobs Water Resources Division was selected by NorthWestern Energy to provide Design-Build services for the Morony Dam Spillway Gate Project near Great Falls, MT. The $29 Million project will consist of the design and installation of new vertical lift roller spillway gates. McMillen Jacobs will also be responsible for:

– Demolition of existing concrete structures, including concrete demolition and gate removal
– Development, improvement, and maintenance of temporary access roads
– Site development and site infrastructure construction
– Concrete construction and retrofit
– Environmental and permitting

Morony Dam has a 390-foot wide spillway with nine radial gates and one sluice gate to control the flow of water down the spillway. The existing tainter gates are at the end of their design life and are susceptible to ice buildup around the seals. McMillen Jacobs is designing new vertical lift roller gates with heated guide slots to replace the outdated tainter gates. The new design uses the latest design codes and ensures the gates are capable of operation throughout the year under all loading conditions. Additionally, a new hoist frame will be designed and installed to allow the gates to be hoisted to the same level as the old tainter gates.

In order to perform this work, the existing spillway bays have to be dewatered one at a time. However, there are no existing maintenance stoplogs at the Morony project. Therefore, McMillen Jacobs must construct temporary upstream stoplog slots that will be designed to accommodate new dewatering stoplogs. The stoplog slots will consist of steel W shapes anchored to the pier noses with custom stoplog bearing seats and guide pins. The construction stoplogs will be designed to span 41 feet between piers while also dewatering up to 32 feet.

Construction is projected to begin Spring 2021 with an estimated completion date later Summer 2023.

McMillen Jacobs has worked with NorthWestern Energy since 2015, providing similar Design-Build services at their Hebgen Dam facility.