The Challenge

Allendale Canal and Fish Screen is part of the Flint Creek Water Project, owned by the Montana Department of Resources and Conservation (DNRC) and operated by the Flint Creek Water Users Association. The Montana Department of Justice’s Natural Resource Damage Program (NRDP) funded the project to improve irrigation efficiency and benefit fisheries in Flint Creek.

The Allendale Canal is the largest and furthest downstream in the Flint Creek Water Project. It often takes a significant percentage of Flint Creek, especially later in the season when irrigation demand peaks from farms around the Drummond area. Allendale diverts Flint Creek water and water stored and delivered from East Fork Rock Creek Reservoir. Many of these ditches were built in the 1930s and 40s and had outlived their service life.

Montana DNRC and NRDP
Philipsburg, Montana
44,000 sf, 250 MGD


  • Alternatives analysis

  • Civil

  • Hydraulics

  • Structural

  • Mechanical

  • Electrical Engineering

  • Permitting

  • Construction inspection

  • Steel

Flint Creek serves agricultural water users around the Drummond area and supports populations of fish including brown and bull trout.

When water levels are low in Flint Creek, whatever water doesn’t go to Allendale Canal, goes into one of the three ditches located about 1,000 feet downstream. A 2016 report from NRDP and Montana Department of Fish, Wildlife & Parks (FWP), showed that in the fall, when the brown and bull trout are migrating upstream to spawn, the existing rock and tarp diversion block upstream movement and fish are unable to reach their destination. The study also determined that a significant amount fish were being diverted into the irrigation ditches and over 450 were found in the first 2,000 feet the Allendale Canal. This project was complex due to the concentration of earthwork, concrete, in-stream diversion, rock placement, and structural, mechanical and electrical design requirements. Adding to the difficulty were some tight tolerances on some of the mechanical pieces, and there was nowhere to divert the creek away from the project site during construction. Contractors were constantly battling flowing water through the site during the construction. In addition, two significant flood events also passed through the site during construction.

The Solution

The completed project prevents fish entrainment, allows upstream fish passage on Flint Creek, and improves the surrounding water delivery infrastructure.

Morrison-Maierle, in partnership with OneFish Engineering and Quadrant Consulting, designed a vertical flat-plate fish screen that now safely excludes fish from Allendale Canal and returns them to Flint Creek through a bypass return pipe.

A Holistic Design

In addition to encouraging fish to stay out of the irrigation ditches and in Flint Creek, Morrison-Maierle and its partners created a holistic design that improved the infrastructure itself by reorienting gates, realigning the diversions and solutions to remove debris (metal grates), and improving bedload sediment (sluice gates).

Morrison-Maierle and its partners were awarded the project in 2016. Consideration was given to consolidating Allendale and the privately-owned ditches, but in the end, they remained in their original locations.

The new irrigation infrastructure includes:

  • Stable roughened riffle diversions.
  • Modern intake structures with gates, debris racks, and sediment flushing gates.
  • Measures to guard against ice, debris, and logs coming down Flint Creek during high flow.
  • New lining and Parshall flumes.
  • Four new fish screens: one large vertical flat plate in Allendale, and three smaller, corrugated water screens in the privately-owned ditches.
  • Designs to help make maintenance and operational duties easier and safer to access.

The Benefit

Morrison-Maierle’s team adopted a holistic design approach during the contracting process to provide necessary infrastructure and help meet the tight construction schedule. The project construction started at the end of October 2020 and was substantially complete by May 2021. Morrison-Maierle, DNRC, NRDP, and Mungas Company were all able to work together to complete the project while simultaneously providing stable irrigation water delivery during construction completion.

During the 2021 season, fish entrainment was effectively eliminated and upstream passage was verified by FWP study. Additional monitoring will continue to verify benefits and provide adaptive management within the irrigators’ operations and maintenance. The irrigators also have new infrastructure that is easier and safer to operate and will provide a more reliable water supply.

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