Introduction:  With the cooperation of the Buhler Family, 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 and fall of 2011.  Design has been completed by AP and topographic survey was done by the ODFW survey crew.  Removal/fill permits will be acquired by AP and 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.

Project Location:  The project area is located on Big Sheep Creek at river mile 6.4 approximately 3 miles above the confluence with Little Sheep Creek, in the Imnaha Subbasin.  It is on private land owned by the Buehler Ranch, and is near Imnaha, Oregon.

*   Legal – T1S R48E Section 8 SE ¼
*   Lat/Lon – 45.4841 116.8409

Existing condition:  It is apparent that sometime in the past a large log, approximately 2 feet in diameter, was placed just downstream of the diversion intake in an effort to increase the water depth in the forebay area.  Over time the forebay area has been filled in with sediment and the streambed in the forebay is now level with the top of the log.  On the downstream side of the log there is a vertical drop in the streambed of approximately 5 feet and then the creek continues at a relatively constant grade.  The drop on the downstream side of the log creates a fish passage barrier, particularly when the creek is experiencing low flows.  Occasionally, a hole is developed upstream of the log and water begins to flow underneath the log.  When this occurs irrigators enter the stream and place material in the hole to repair the check structure.  This causes disturbance in the streambed and turbidity in the creek.

Project Objectives:  

1.   Provide year round passage for all life stages of aquatic organisms.

2.   Reduce sedimentation from periodic structure maintenance activities.

3.   Promote natural bedload transport through this stream channel.

Construction: The project will be constructed during the in-stream work window for this reach of the Imnaha River during the summer of 2011.  Anticipated work includes mobilization, material delivery, project construction, site clean-up and final grading, and demobilization.  The instream work window is between July 1st and October 15th with instream extensions possible.  The construction phase of this project is expected to last no longer than the instream work window.  Construction will be complete by October 15, 2011 and planting will continue into the fall of 2011.    

Benefits:  When complete this project will have addressed a multitude of instream parameters of concern in Big Sheep Creek at the project site.  Aquatic passage is the primary concern especially in the summer months when Big Sheep can experience warm stream temperatures.  More than 30 miles of habitat exists above this diversion on Big Sheep alone and tributary streams offer many miles more.  Habitat conditions upstream are variable but cool water is characteristic.  While not common the current diversion does need to be fixed periodically.  This activity disturbs the channel and causes sedimentation.  The new structure will be more stable and maintenance activities will be eliminated or reduced.