L-63/Big Timber Creek Siphon

Project Narrative

This project installed a siphon to separate Lemhi River irrigation water from Big Timber Creek, improving fish passage conditions by removing an impassable barrier for ESA-listed juvenile and adult Chinook salmon, steelhead and bull trout attempting to migrate through the lower reaches of Big Timber Creek. Completion of this project also provides a hydraulic benefit by creating a stream channel that will accommodate high spring flows that are proposed in the Lemhi Agreement as a conservation measure to improve stream habitat conditions in the Lemhi River. This project was a first step to removing a total of three identified fish barriers for the purpose of reconnecting Big Timber Creek with the Lemhi River. Prior to project completion, the canal from the L-63 irrigation diversion off of the Lemhi River crossed the Big Timber Creek channel, co-mingling water from the creek and irrigation canal. During irrigation season – March 15-November 15, the entire creek channel was blocked off with boards, blocking passage for water and fish. The newly installed siphon now carries Lemhi River water in the L-63 ditch underneath of the Big Timber Creek channel, thereby removing the previously existing barrier and establishing a natural stream channel in its place. The siphon design includes a controllable by-pass channel to allow overflow from the ditch into the Big Timber Creek if necessary during a high water event, or to prevent ice build up under Highway 28. This by-pass channel will also serve as a fish barrier to prevent passage of fish between lower Big Timber Creek and the L-63 canal.There were no deviations, with the exception of the original cost of the project, as originally proposed.The actual performance of this project is yet to be determined, and will not be fully observed and evaluated until high water flows occur in spring 2007. It is, however, expected to meet or exceed this performance measure. Completion of this project is a first step to reconnection Big Timber Creek with the Lemhi River. Upon completion of all three Big Timber Reconnect projects in 2007, approximately 60 miles of stream will be made accessible.This project will be included in the Upper Salmon Basin Watershed project (USBWP) monitoring schedule and will be monitored by the USBWP or its representatives. Monitoring points will be set up before project implementation. The project will be inspected and certified when completed if it meets the standards and specifications stated in the contract with the Lemhi Soil and Water Conservation District. Additional photo-point monitoring will occur at 5 year intervals for the life of the landowner contract. Monitoring information is collected according to the USBWP monitoring plan recorded and stored at the USBWP office in Salmon,Idaho.Installing a siphon to separate Lemhi River irrigation water from Big Timber Creek will improve fish passage conditions by removing an impassable barrier for ESA listed juvenile and adult Chinook salmon, steelhead, and bull trout attempting to migrate through the lower reaches of Big Timber Creek. This project also provides a hydraulic benefit by creating a stream channel that will accommodate high spring flows that are proposed in the Lemhi Agreement as a conservation measure to improve stream habitat conditions in the Lemhi River.