Introduction

With the cooperation of the Lostine Ditch Company, technical assistance from ODFW, and engineering services of Anderson Perry (AP) the GRMW will complete this diversion structure replacement project during the instream work window in the summer of 2012.  AP has accomplished survey and design and will acquire removal/fill permits.  The GRMW will accomplish all other environmental compliance requirements.  The GRMW is the project sponsor and responsible for all contracting and AP will supply construction engineering.  The resulting project will be a diversion structure that requires minimal annual instream maintenance, results in reduced erosion and sedimentation, and improves aquatic passage conditions.

Existing Condition

The existing diversion structure was built in the early 1960’s, is aging, has been repaired in the past and restricts passage of juvenile anadromous and resident fish at some flows.  Past repairs have included shoring the channel spanning concrete walls with rock to prevent potential failure and piling debris below the structure to improve passage conditions.  These efforts have improved structural integrity and passage conditions but were intended as temporary fixes until a new facility can be constructed.  This aging structure does not meet State and Federal fish passage criteria as currently applied.

Currently the Lostine Ditch Diversion is used during the Wallowa Valley irrigation season, which starts on May 1st and ends on September 30th.  At all times of the year this ditch delivers stock water at a much lower rate than during irrigation season.  A fish screen composed of three paddle wheel operated drums is located near the diversion.  Adjacent to the diversion is a concrete step-pool type structure composed of five steps.  The steps span the width of the river and each has two to three notches approximately 3 feet wide.  The elevation difference between each step is approximately 15 inches, which exceed fish passage criteria.  Downstream of the steps is large riprap and debris such as concrete pieces, wood, etc., that provide scour control.  

The project site will be constrained by two existing structures.  A private bridge located approximately 400 feet downstream of the diversion head gate precludes altering the river on the downstream end of the project site.  The upstream wall of the fish ladder serves as the existing irrigation diversion structure and constrains the project on the upstream end.  The irrigators served by the ditch have requested not to modify the most upstream step of the diversion structure.  The designs as presented in this proposal do not call for a modification of the most upstream step.

Fish that are native to the Lostine River include spring Chinook, summer steelhead, rainbow trout, and bull trout as well as other resident species.   Design criteria to pass spring Chinook, bull trout, and steelhead are the most stringent and have been used for design purposes.

Spring Chinook migrate through the Lostine system to their spawning areas between mid-June and mid-September.  Summer steelhead migrate to their spawning areas in late winter and spring.  Bull trout utilize the project site as a migratory corridor between upstream spawning areas and downstream rearing and foraging areas, typically migrating upstream in late spring and early summer and downstream in late fall.  Temperature and turbidity are two environmental factors that can affect migration patterns of fish.  As temperatures start to rise, fish tend to move upstream into cooler waters.  Turbidity, especially when coupled with high flows, may temporarily inhibit fish movements.

Benefits

When complete this project will have addressed a multitude of instream parameters of concern in the Lostine River at the project site.  Aquatic passage is the primary concern especially in the summer months when the Lostine can experience warm stream temperatures.  Habitat conditions upstream are variable but cool water is characteristic further upstream.  While uncommon, the current diversion does need to be fixed periodically which disturbs the channel and causes sedimentation.  The new structure will be more stable and maintenance activities will be eliminated or reduced.  Advantages of the chosen design alternative include:

1.   Provide a more natural channel than what currently exists.
2.   Improved fish passage.
3.   Low diversion structure maintenance.