RELATIONS AMONG HYDROGEOMORPHIC PROCESSES, SAND MOVEMENT, AND BROOK TROUT HABITAT REHABILITATION FOR LAKE SUPERIOR SOUTH-SHORE STREAMS, WISCONSIN

Streams along the south shore of Lake Superior had large brook trout populations before European settlement and logging (pre 1870s). In the 1990s, there was renewed interest by fisheries biologists to rehabilitate degraded brook trout populations. Results from studies of surface runoff, ground-water flow, and geomorphic processes indicated that brook trout spawning and survival depends on flooding severity, regional ground-water discharge zones, and amount of erosion/sedimentation. Historical logging and subsequent agriculture increased flood peaks and erosion/sedimentation rates but did not affect regional ground-water flows.

The Bark River, a forested Lake Superior south-shore stream, has a small brook trout population. Reconnaissance along the Bark River indicated that steep ephemeral gullies have episodic mass wasting and incision. Downstream of the gullies, perennial reaches have sand sedimentation, accentuated by steep topography and geologic structure, logging practices, and beaver activity. Sand accumulation upstream of beaver dams and logging structures caused wide channels and promoted growth of early successional riparian species, such as alder. Presettlement riparian vegetation was dominated by conifers.

Rehabilitation of the Bark River has focused on erosion control in ephemeral gullies and sand removal in perennial reaches. Techniques tested on gullies include grade control (mainly natural, onsite materials), addition of large woody debris for increasing roughness, slowing and infiltrating flow and trapping sediment, and native plant restoration. For perennial reaches, rehabilitation has included active strategies to move the riparian forest toward presettlement community of conifers, including alder removal. Headcutting, incision, bank erosion, and sediment deposition along ephemeral gullies are monitored through semi-annual measurements of valley cross sections, erosion pins, and clay pads. Flow and suspended sediment concentrations are monitored in perennial reaches upstream and downstream of gullies with rehabilitation as well as a control gully. Habitat and brook trout populations are surveyed annually. Results from this multi-agency study will be used to evaluate stabilization techniques and alternative forestry practices for use on other streams.