73982 REL 133

1996-046-01 EXP NURSERY BRIDGE (PHASE II-III): PASSAGE & FUNCTION

4/1/2021

12/31/2023

184. Install Fish Passage Structure

Work Element Usage Report

G: 184 - [CCR-46814]: Mill Creek Intake Dam Fishway Improvement

[CCR-46814]: Implement improvements to the fishway at the Mill Creek Intake Dam. Upon completion of the project, the City of Walla Walla's Mill Creek diversion fishway will have been modified to be in compliance with all applicable state and federal fish passage requirements.

Background: The Mill Creek Intake Dam was constructed in the 1920's and supplies municipal water to the City of Walla Walla. The diversion consists of a 17-foot tall concrete dam, screened intake facility at the river right abutment, and a vertical slot fishway at the river left abutment. The fishway was originally constructed as a result of the Mitchell Act of 1938 and ownership of the fishway is unclear. The fishway was reconstructed in 1988, but a 2010 inspection by the Washington Department of Fish and Wildlife identified deficiencies with attraction flow at the fishway entrance and loss of hydraulic head at the fishway exit.

Overview: The design was completed in 2019 by the CTUIR Fish Passage Operations project; the Walla Walla Fish Habitat Enhancement Project #1996-046-01 will provide permitting and implementation support. The design includes improvements to the fish ladder entrance to increase the attraction jet and deepening the exit to improve hydraulics through the fishway, as well as providing increased access for fishway maintenance and increased occupational safety design considerations (e.g. tie-off points).

The improvements to the Mill Creek Intake Dam Fishway will improve passage conditions for all life stages of ESA-listed Middle Columbia steelhead, ESA-listed bull trout, and spring Chinook salmon. The proposed design will bring the fishway into compliance with Oregon Administrative Rule 635-412-0035 (Fish Passage Criteria) and National Marine Fisheries Service Anadromous Salmonid Passage Facility Design (NMFS 2011) criteria.

The Middle Columbia River Steelhead Recovery Plan (NMFS 2009) notes that a recovery scenario for the Middle Columbia River DPS includes a viable population in either the Touchet River or the upper Walla Walla River. This project will decrease passage burden on Middle Columbia summer steelhead returning to the Mill Creek watershed and allow unimpeded access to over 18 miles of undisturbed, protected spawning and rearing habitat in the Mill Creek Watershed. Improving fish passage in Mill Creek is identified as a specific action to achieve prioritized strategies for improving summer steelhead populations in the Snake River Salmon Recovery Plan for SE Washington (SRSRB 2011).

Improve conditions and complete modifications to the Mill Creek Diversion Dam Fishway; restore fish passage at the fishway that meets state and federal passage criteria.

$158,750

72.35%

12/03/2021

12/01/2023

08/15/2022

Concluded

[Unassigned]

[Unassigned]

Finite