Chadbourne Diversion Retrofit and Fisheries Enhancement

The Chadbourne Diversion is located on the Shields River approximately 9.2 valley miles upstream (14 river miles) of the Yellowstone River. The ~68 foot concrete diversion has supplied water to irrigators and livestock since its construction around 1930. As an additional benefit, the structure has limited invasion of non-native rainbow trout into the Shields River watershed above the diversion. Fish Wildlife and Parks contracted with AESI, in conjunction with OASIS Environmental, to design and oversee construction of the project. The work consisted of several components. The primary focus involved a diversion retrofit to increase the stability of the structure and to provide a more formal fish barrier. Additionally, to allow selective fish passage for Yellowstone cutthroat trout, a fish trap structure was designed on the bank of the river and will allow biologists to sort and selectively transport fish upstream of the diversion. The project was funded by a Montana DNRC RRGL grant and a Montana FWP Future Fisheries grant. Federal funding was provided by the Forest Service, the US Fish and Wildlife Service and the National Fish & Wildlife Foundation. Private donations were provided by the Lower Shields River Canal Company and Trout Unlimited.

Project elements included:

• An in-depth geotechnical and structural evaluation of the diversion to establish the suitability of the structure for retrofit;
• Design of a concrete ogee weir retrofit to increase the stability of the weir while providing fish barrier weir hydraulics;
• Design of a step-pool and fish trap structure on the bank of the river;
• Construction ready plans and specifications; and
• Completion of construction ready documents on schedule and within budget.