Moving toward sustainable irrigation in a southern Idaho irrigation project

Private and public irrigation development projects were a fundamental part of bringing irrigation arid regions of the western U.S. The Twin Falls Canal Company in southern Idaho provides a case study of private and public irrigation development because the project was developed by private investors under the Carey Act and receives a portion of its irrigation water from Bureau of Reclamation reservoirs. The project survived initial financial struggles and waterlogged soil to focus on sustaining the production by reducing chronic furrow irrigation erosion and nutrient losses in irrigation return flow. Average sediment loss from the project was 460 kg/ha in 1970. A cooperative effort by the canal company, state and federal agencies, and farmers improved water quality by installing sediment ponds on fields, applying polyacrylamide with furrow irrigation, converting from furrow to sprinkler irrigation, and constructing water quality ponds on irrigation return flow streams. From 2006-2018, the project retained on average 165 kg/ha of sediment and 0.4 kg/ha of total phosphorus annually, which removed 13,000 Mg of sediment and 33 Mg of total phosphorus from the Snake River each year. Nitrate-N from subsurface drainage, however, was lost at 10 kg/ha each year, which is equivalent to 380 Mg of urea fertilizer from the entire project. While sediment and phosphorus concentrations in irrigation return flow have decreased, they were still greater than the irrigation water concentrations, indicating that more can be done to reduce the project’s influence on water quality in the Snake River