Goal for the Bitterroot River Floodplain and Associated Wildlife

Overview

The Bitterroot Valley is bisected by the Bitterroot River, which originates in the Anaconda-Pintler Wilderness and the Bitterroot Mountains and flows north to empty into the Clark Fork River near Missoula. Alongside the river are riparian habitats consisting of woodlands (riverfront and gallery forest), scattered grasslands, and wetlands. The riparian woodlands of the refuge consist of 483 acres of riverfront and gallery forest. The tree community of the 160 acre WVA has been sampled; analysis/report here. The wetland component of the refuge’s riparian habitat community is 20 acres of oxbows, sloughs, remnants of former gravel pits and creeks—specifically, Barn Slough, Oxbow, North Island Slough, Francois Slough, North Burnt Fork Creek, and Three Mile Creek. Each community has different vegetation and succession requirements.

The Service has identified the habitat needs of a diverse group of target floodplain species, including waterbirds, neotropical migrants, and mammals (table 8 of the Refuge CCP). Providing for the life history needs of these species will provide the natural floodplain habitat diversity and conditions needed not only for these targeted species, but also for a broad suite of other floodplain associated wildlife. Monitoring will focus on these target species to determine their response to floodplain management actions.

The diversity and productivity of the Bitterroot River Valley at and near Lee Metcalf Refuge was created and sustained by a diverse floodplain surface that was seasonally inundated each spring from both flooding of the Bitterroot River and drainage or seepage from surrounding mountain slopes. Occasional overbank and more regular backwater flooding from the river into its floodplain at the refuge historically helped create and sustain communities and basic ecological functions and values of the site. These flooding processes on the refuge are now restricted by levees along the river, levees and dams on constructed wetland impoundments, roads, the railroad bed, and dams or other obstructions on tributary channels (go to "Past Actions" webpage for historical management overview).

To restore the floodplain system at the Lee Metcalf Refuge, restoring the capability of the Bitterroot River to overflow its banks and to back water up tributaries and into other floodplain channels is desirable. The seasonal “pulsed” flooding regime provided uninhibited movement of water, nutrients, sediments, and animal between the river and the floodplain and supported life cycle events and needs of both plant and animal communities. Periodic long-term floods are also important floodplain processes that help maintain community dynamics and productivity. For example, overbank flooding deposits silts and nutrients in floodplains that enhance soil development and productivity. Overbank flooding also creates scouring and deposition surfaces critical for germination and regeneration of riparian woodland species, especially cottonwood (Heitmeyer et al. 2010). Backwater flooding provides foraging habitat for pre-spawning native fish and rearing habitat for larval and juvenile fishes. Annual backwater flooding recharges water regimes in depressions and shallow floodplain wetlands that serve as productive breeding habitat for amphibians, reptiles, waterbirds, and certain mammals. Subsequent drying of floodplains concentrates aquatic prey for fledgling waterbirds. Collectively, the body of scientific evidence suggests that restoring the hydrologic connectivity between the Bitterroot River and its floodplain at Lee Metcalf Refuge is desirable (Heitmeyer et al. 2010).

The Service will work with engineers and hydrologists to determine the location, design, and steps needed to effectively restore natural waterflow without damaging other refuge resources or neighboring lands. Some of the options include completely removing levees, breaching them, or constructing a spillway to allow water to pass through a specific area.