Lapwai Creek Reach 14 Floodplain Restoration

This project was successful in treating and or protecting 0.64 miles of stream. Per Alta Science and Engineering Final Design Plans 14 instream structures were built with excavated pool and run/riffle sequences associated with them. The levees that were present in the reach were removed allowing the stream to access 5.5 additional acres of floodplain. Over a 5.5 acre area noxious weeds were treated both with herbicide and mechanical removal. New meanders were introduced into the reach with the construction of new stream channel.

The Lapwai Creek Reach 14 Floodplain Restoration Project was slated for implementation during the in-stream work window of August 1 2018 through October 31, 2018. Due to the selected contractor getting a late start on the project because of a conflicting schedule, an extension on the in-stream work window was sought and granted allowing work to occur until November 30, 2018. The material on site was much larger and angular in form than was anticipated and the cut/fill volumes estimated by the Design Engineer were off by a large factor (4000 cubic yards of excess material instead of the estimated 750 cubic yards). Due to the reasons above not all aspects of the project were able to be completed by the planned date. The project area experienced an unusual cold snap in late November that froze the ground solid to a depth of 18 inches making revegetation of the site as well as construction of the side channel impossible until the following year. An amendment was received from OSC to extend the contract for one year, to 12/31/2019.
During the spring high water event of 2019 the project area experienced some very extensive head cutting and incision along roughly a 400 foot section of newly constructed stream channel. A side channel also formed during the spring high water event, the side channel also experienced head cutting and deep incision. Due to the amount of material that was redistributed in the project reach revegetation was put on hold until a short term solution could be identified and a long term plan put into place to address current conditions at the project site. Bonneville Power Administration (BPA) Engineers visited the project site in September 2019 and worked with NPT staff in identifying a short term fix to ensure passage at all flow levels for all aquatic organisms at the headcut location. Then, the spring high water event of 2020 changed the project area drastically again. The stream moved laterally and completely abandoned the newly constructed channel at the location of the passage barrier.

NPT is now at a point where BPA engineers are looking at the project and are working on putting together an appropriate design to address the current issues facing the project area. BPA and Nez Perce Tribe SRBA funds will be used to design and potentially implement a future project at this location.

Lapwai Creek is a tributary to the Clearwater River and is a restoration priority watershed for the Lower Mainstem Clearwater River steelhead population of the Clearwater River steelhead MPG of the Snake River steelhead DPS. Work to be implemented include priority actions identified in the NMFS 2016 proposed recovery plan for this MPG and include the following: 1. Restore hydrologic processes. 2. Restore channel-forming processes by reestablishing floodplains in incised channels, removing or setting back flood control structures, and rehabilitating stream channels that have been straightened. 3. Reestablish riparian vegetation to improve LWD recruitment and create shade for streams. 4. Reduce fine sediment delivery to streams where it is caused by road drainage systems.