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  • Biological Assessment for Bridge Replacement Project

    Due to the presence of bull trout within a creek associated with a bridge replacement, a Section 7 consultation was required under the Endangered Species Act. A biological assessment to determine the effects on bull trout and their habitat was conducted by analyzing the appropriate habitat indicators, both terrestrial and aquatic, then quantifying the project impacts within the stream reach. To mitigate the effects of the project, a minimization plan was developed that included diverting the stream, designing soft bank armoring, ensuring riparian preservation, and incorporating Best Management Practices (BMP) strategies to limit impacts. By utilizing Geographic Information Systems along with incorporating U.S. Army Corps of Engineers (USACE) Hydrologic Engineering Center – River Analysis Program (HEC-RAS) modeling, the size of the stream diversion structure was calculated for the predicted flow rates. Hedge brush layering was incorporated into the minimization plan to stabilize impacted banks, increase the roughness coefficient along the stream edge and decrease near bank stress. In addition, the plan included many Montana Department of Environmental Quality (MDEQ) approved erosion and sediment control measures along with a final stabilization strategy.

    The stream corridor associated with this project is located within the U.S. Fish and Wildlife Service (USFWS) National Wetlands Inventory; therefore, wetland delineation to quantify habitat impacts was required by the USACE. Field assessments were conducted which included surveys of vegetation, soils, and hydrology. The wetland area was delineated using a Trimble GPS unit and a disturbance area was estimated. The wetland impacts did not exceed 0.10 acre of disturbance, therefore, a compensatory wetland mitigation plan was not necessary.

    The biological assessment and the minimization plan, along with the other permitting requirements, were approved by all federal, state, and local agencies involved. Engineering oversight was conducted during project implementation to ensure permit compliance and proper channel restoration techniques were utilized.