The Island Creek Project will restore habitat for salmonid spawning and rearing tributary to the Boise River for the purposes of restoring designated beneficial uses that are not fully supported in the Boise River. The channel will be about 3,300 feet (slightly over 1/2 mile) in length.
Island Creek is located near Eagle, Idaho, west of Linder Road, on Eagle Island and serves as a drain and flood overflow channel to the South Channel of the Boise River. Island Creek drains the interior of Eagle Island through the Three Rivers Ranch. Reasonably stable flows in Island Creek derive from being downstream of the Eagle Island research fish hatchery and water table influence. There are no direct connections providing water from the Boise River to Island Creek, other than through overbank flooding (around 7,200 cfs). Normal flows on Island Creek appear to be around two to eight cfs, with an estimated average of about six cfs.
The Boise River is one of the few rivers within a rapidly urbanizing area with a naturally spawning rainbow and brown trout population. Numerous dams and diversions in the Boise River system prevent the natural processes of streambed movement of larger and smaller gravels, channel formation, and other ecological processes of a riverine environment. Habitat studies of the Boise River (e.g., Asbridge and Bjornn 1988) found the river lacks suitable spawning and rearing habitat. Restoring side channels to the river is recommended because few remain (Blew et al 2001).
The Island Creek channel on Eagle Island represents the greatest potential for significant side channel development in this area of the lower Boise River. A new side channel would benefit the Boise River by providing quality trout spawning, rearing, and winter holding water. The project would involve a partnership of Trout Unlimited, the landowner, the Natural Resource Conservation Service, and other parties in the design and construction of the side channel. Vegetation and fish population growth will be monitored with the assistance of Idaho Fish and Game and Trout Unlimited.
The exact undisturbed condition of Island Creek is unknown. However, the geomorphic and vegetative characteristics of a relatively undisturbed condition can be inferred by examining the hydrology, adjacent soil types, and similar waters in the Boise River floodplain. Design goals aside, significant problems exist at Island Creek that can be identified, and we can concentrate on fixing the existing problems while aiming at functions and values that would be provided by a creek with minimal disturbance. Island Creek currently is in a severely deteriorated condition as evidenced by channel geomorphology, lack of a diverse overstory of wetland and riparian species, and a significant aquatic weed problem.
Island Creek could become a significant value to the Boise River. The creek has an ideal discharge for a small, productive trout stream. The creek has sufficient grade to produce velocities capable of providing ideal spawning habitat. The creek has an overall low sediment production that is attractive to producing quality pools. The low sediment production is due to a lack available upstream sources of sediment and streamflow energies sufficient to move the sediment. Unfortunately, the creek is in such a degraded condition and has such low sediment production that reasonably fast recovery is not possible. Therefore, the project intends to construct a basic channel that will provide many of the features that are currently limiting factors.
The purpose and goal is to restore a 1/2 mile side channel to the Boise River to provide optimal spawning, rearing, and winter holding habitat for aquatic species, with the capability to increase the restoration activities to 2 miles along the Boise River.
Based on the limiting factors and potential of Island Creek, the following design goals are proposed:
The result is a sinuous stream with a low width-depth ratio, quality pools, capable of moving fine sediments through potential spawning areas.
Near-term Resource Objectives:
Long-term Resource Objectives:
Construction Technique:
We expect the side channel restoration of spawning and rearing habitat will enhance the naturally spawning populations of brown trout and rainbow (redband) trout and white fish in the Boise River. The results and lessons learned will be transferred to additional areas where habitat restoration and connectivity can occur along the Boise River. Other likely candidates include Harris Ranch (currently funded in part by National Fish and Wildlife Foundation) the "daylighting" of Cottonwood Creek through Julie Davis Park in downtown Boise, improving habitat in the Loggers Creek side channel in southeast Boise, and side channels adjacent to the city-owned Warm Springs Golf Course.
Questions or comments send to: tutedtrue@aol.com
Ted Trueblood Chapter Idaho Trout Umlimited
