Presenter/s: Erin Plue
Symposium Session: 2023 - 12 All that glitters is not Gold: Restoring Dredged Rivers
Topics covered: dredged rivers, floodplain, idaho, riparian, and sediment transport
ABSTRACT
From 1917 through 1926, a floating bucket dredge turned over five miles of the floodplain of Prichard Creek, a tributary to the North Fork Coeur d’Alene River in the Idaho Panhandle. The dredge left behind hundreds massive U-shaped piles of large cobble with small ponds scattered throughout the piles and sent the finer sediments either floating downstream or buried dozens of feet below the surface. These impacts paired with other placer mining, extensive historic logging, and infringing infrastructure have left the drainage with significant impacts.
Even with the significant challenges facing Prichard Creek there are many reasons that its restoration has been prioritized in the Coeur d’Alene Basin. Prichard Creek has some of the coldest water in the basin and most of the riparian area remains undeveloped with minimal recent impact. Ten and half miles of Prichard Creek’s 14-mile length is owned by a private lumber company, Idaho Forest Group, who is a dedicated partner in the restoration project and is in the process of putting the property into a conservation easement that will restrict future mining, development and subdivision of the land. This is a rare gem in an area with heavy recreational use and intensive streamside development.
Prichard Creek’s cold water is an appealing refuge for local Westslope Cutthroat Trout, but their access is restricted to the bottom four miles of stream during the heat of the summer due to subsurface flows. The path of the water once it drops out of the channel is complex and not readily apparent or predictable from the surface. Ground water monitoring stations were installed in 23 spots throughout the dredged reaches of the stream in fall of 2021 to help better understand where water is moving in this chaotic landscape. With a greater understanding of where and why of the route of the water within the Prichard Creek floodplain, alternatives for restoration have been developed in the past year.
As the first phase of restoration is set to start this summer on the bottom four miles of stream channel, the project partners have been in the process of ranking the alternatives for restoration on the remaining project area and committing to a path forward. Understanding the likelihood for success and the costs is paramount in helping the partners commit to a restoration alternative. What is the most desirable result for Prichard Creek? Is it really feasible to restore flows throughout the whole channel all year? Will there be impact to the water temperature? What are the risks and what is the chance of failure? What is the likelihood of finding funding for these alternatives? Are partial fixes worth the effort? These are some of the hard to answer questions that the project partners have been wresting with. Understanding the impacts that have occurred on Prichard Creek has been complex and helping the project partners navigate the most desirable path forward may be just as much of a challenge.