Project Name:  Poley Allen Diversion Structure Modifications

Applicant: Wallowa Soil and Water Conservation District

Participating Landowners:
· Poley Allen Ditch Company
· Bureau of Reclamation
· Natural Resources Conservation Service
· Wallowa Soil and Water Conservation District

Project Contacts:
· Cynthia Warnock, Wallowa SWCD (541) 426-4588
· Darrell Dyke, BOR Engineer, La Grande, OR. 541 963-4178

Project Location: T. 1S, R43E Section 15, on the Lostine River approximately .75 miles south of Lostine, OR.

Project Objectives:
· Improve passage conditions at the Poley Allen diversion structure for adult and juvenile fish.
· Stop the head cut which is undercutting the new diversion structure

Project Description: A concrete structure to divert water into the Poley Allen ditch was installed in 1997 to replace an annual gravel push up dam. The structure was installed utilizing funds from the landowners, Bureau of Reclamation and Bonneville Power Administration. The structure was designed by NRCS and BOR.

The diversion structure design consists of a concrete floor 12 feet in width and 30 feet long, and 3 feet in depth. On the downstream side of the structure, large boulders were placed 10 feet past the end of the structure along the entire 30-foot length. Fish passage was provided on the west side of the structure via a 4-foot wide concrete channel 1 foot in depth and 12 foot in length.

The structure improved fish passage conditions during the first year of use. During the 1998 spring runoff, flows near 2300 cfs caused erosion and movement of the large boulders placed downstream of the structure. Many of the boulders were moved downstream, resulting in up to a 4-foot drop below the concrete structure. The movement of rock and resultant drop has created a fish barrier at the Poley Allen diversion structure.

Inspection and survey at the structure, in the spring of 2000, revealed two problems with the current structure configuration. First, it was discovered the structure was designed only to pass flows of 1400 cfs.  Spring runoff in 1998 exceeded 2300 cfs, creating supercritical flow conditions. The water energy created under cut the 3 and 4 foot diameter rocks placed downstream of the structure. Second, when the Poley Allen structure was completed, a side channel used to convey water around the work site was inadvertently cut off. The original design utilized the side channel to pass flows in excess of 1400 cfs. When the side channel was inadvertently blocked, all flows were routed through the structure.

In order to correct the problems at the Poley Allen structure, and to improve fish passage the following modifications have been planned:
· Install two rock chevron weirs downstream of the structure. Each weir will consist of 200 yards of 3 to 4.5 foot rock placed across the channel as shown in the attached drawing. Small fish passage pools will be incorporated into the structure to insure juvenile passage.
· Lower and harden with rock and sheet piling the inlet to the upstream side channel enabling water to flow through the side channel during high flows, reducing flows through the structure.
· Fish passage near the headgate will be improved by removing a 6" x 4' concrete lip upstream of the headgate. An automated headgate will also be installed to regulate flows into the ditch.

Benefits: The weirs will stabilize the under cut by creating one large pool downstream of the structure. The combination of weirs and pool will dissipate the energy generated as water flows through the structure. During high flows, the pool will decrease the energy gradient or water velocity through the structure. During low flows, pools incorporated in the weirs will provide better passage conditions for all fish life stages. Reconnecting the upstream side channel will reduce flow and water velocity through the structure. This will improve passage conditions through the weirs and concrete structure.

Work Dates:  The project will be completed during the normal instream work window of July 1st thru Aug. 1st, 2005.

Maintenance: The Poley Allen Ditch Company will be responsible for all maintenance of the structure.

Permits - Consultation with NMFS and USF&W will be necessary for ESA compliance. The SWCD will apply for the fill and removal permits from DSL and COE.

Monitoring Plan - BOR and NRCS will monitor the structure for the next 5 years to assess function of the weirs and side channel. The SWCD will prepare annual reports for 5 years and provide copies to GRMW. The Poley Allen ditch will monitor the site for invasion of noxious weeds and control them as needed basis.