Sweetwater Bridge and Stream Design

The Nez Perce Tribe completed 100% designs for channel realignment and bridge replacement on a 0.20 mile segment of Sweetwater Creek near the confluence of Sweetwater Creek and Lapwai Creek in Idaho. The designs addressed current habitat conditions including a straightened stream segment with little to no large woody debris, is confined by Webb Road and an agricultural field, no side channels or lateral habitat, and limited floodplain access due to infrastructure and agriculture. The stream is confined by a concrete wall forcing it into an undersized and aging bridge. The current bridge has a 100-year backwater level of two feet and an overtopping flood at the 2-year interval. This leads to frequent juvenile salmonid stranding in the adjacent agricultural fields.

The completed designs for the Sweetwater Bridge and Stream Project include a new properly sized AOP bridge which meets county bridge requirements, will pass the 100-year flood event, that will allow passage for all life-stages of salmonids, other fish and aquatic organisms, large wood, and substrate, a realigned main channel with increased floodplain access, one side channel, and three more high flow channels. Designs also include 16 in-stream large wood structures, 8 floodplain large wood structures, and 1440 native trees and shrubs. Implementation for the restoration phase of this project has been funded by PCSRF project 006 25 CW and will occur in 2027.

This project was completed under budget due to bids coming in less than expected.

Designs for a properly sized bridge and more complex stream segment (including large wood, pools, and stream length) would greatly reduce juvenile salmonid stranding, directly increase Essential Fish Habitat for ESA listed Steelhead and reintroduced Spring Chinook and Coho Salmon, expand floodplain access, and increase native riparian vegetation including large woody species.