Abstract: Session A 11:45 am (Back to Session A)
Restoration of Mining Impacted River and Floodplain Ecosystems in Montana: A Case Example from Ninemile Creek in the Middle Clark Fork River Watershed
River Design Group, Inc.
Contributing Authors: Paul Parson, P.E., Trout Unlimited
Traci Sylte, P.E., Soil, USDA Forest Service, Lolo National Forest
Montana has a rich history of placer (gravel) mining dating back to the early to mid-1800’s. Although many of Montana’s larger placer mining operations have ceased in recent decades, the legacy of these operations still persists on the landscape in many of Montana’s most treasured watersheds, including Ninemile Creek located in the Middle Clark Fork River watershed approximately 20 miles west of Missoula, Montana.
With a contributing area of approximately 186 mi2, the Ninemile Creek watershed originates in the Ninemile and Reservation Divides of the Lolo National Forest and flows 26 miles to the confluence with the Clark Fork River near Huson, Montana. Placer mining with draglines, dredges, hydraulics hoses and sluicing began in 1874 and continued until the late 1940’s on both the mainstem Ninemile Creek and primary tributaries. Alluvial gravels were worked into numerous tailings piles ranging from 10 feet to over 40 feet in elevation above the stream channel. The mining process reworked the glacial and fluvial sediments leaving behind a highly altered river and floodplain ecosystem.
In 2003, Trout Unlimited and the Lolo National Forest in cooperation with federal, state, and local agencies initiated a comprehensive restoration program to rehabilitate a seven-mile reach of Ninemile Creek within the Housum Placer, a private 250-acre patented mining claim. An interdisciplinary team of restoration professionals developed designs for reconstructing the likely pre-mining conditions of the valley including stream channels, floodplains, and terraces. To address the lack of historical information, an extensive data collection and analysis effort was undertaken to understand pre-mining processes and valley characteristics. Data collection included acquisition of LiDAR and channel bathymetry, soil investigations, field calibration of project hydrology and regional regression analyses, as well as sediment transport, hydraulic, and geomorphic investigations, and vegetation community mapping.
This presentation provides an overview of the Ninemile Creek restoration program, which has spanned four construction phases, three miles of channel restoration, 32 acres of riparian floodplain restoration, and four tributary reconnections. Presentation content will include examples of restoration techniques, challenges faced, and how those challenges were overcome.