Sweetwater Bridge and Stream Design

The Nez Perce Tribe will design a 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. Current habitat conditions include a straightened stream segment which contains little Large Woody Debris, is confined by Webb Road and agricultural fields, no side channels or other lateral habitat, a floodplain that has been converted to agricultural or cut off by the county road, and limited riparian vegetation. 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.



Project actions include: 100% designs for 1) A bridge that will pass flows of a 100-year event, meet county bridge requirements, allow full aquatic organism passage at all flows, and 2) a properly aligned stream channel that will increase length and complexity (including large wood, side channels, pools, and cover), increased access to floodplain and adjacent riparian habitat, and properly intersect with the county road and bridge. Completed designs will be used for projected implementation in 2026.

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.