Idaho officials broke ground on Oct. 14, 2025, on a two-year, $20 million project designed to upgrade and modernize the nearly 100-year-old Ridenbaugh Diversion Dam on the Boise River, according to idahocapitalsun.com.
Nampa and Meridian Irrigation District officials are replacing and upgrading the dam, which is just east of Barber Park, a popular destination for people who float the Boise River each summer.
Gov. Brad Little called the dam "a powerhouse in the Treasure Valley," adding that the project will ensure farmers continue receiving much-needed irrigation water, idahocapitalsun.com reported.
"This project in particular will be a modernization into the 21st century, but it also has a safety and a fish aspect to it," Little said. "So, this is not just a pure irrigation project. It really checks all the boxes for what's important in Idaho."
Some of the funding for the $20 million dam project comes from $30 million that Little and the Idaho Legislature set aside during the 2025 legislative session for water infrastructure projects.
The irrigation district received approximately $10.7 million from the Idaho Water Resource Board, which was a portion of the $30 million for water infrastructure projects. The irrigation district also received an approximately $4.7 million Bureau of Reclamation Watersmart Grant, according to idahocapitalsun.com.
The dam's purpose is to raise the water level, allowing Boise River water to be diverted into the Ridenbaugh Canal. From there, it is delivered to farms and lawns across the Treasure Valley for irrigation.
Officials said the existing dam, which dates to the 1930s, is antiquated.
A crew of three must install and remove 20-ft.-long boards by hand — even in bad weather — to raise the water level, according to idahocapitalsun.com.
A new automated system that includes gates and an 80-ft. weir extending from the crest gate to the north riverbank will replace that system.
Two-stage temporary cofferdams will be constructed in the Boise River to dewater one side of the river and allow flow through the other side, according to the Idaho Water Resource Board. A curved concrete intake will be constructed on the south bank. The new intake structure will include a sediment settling basin and gate to minimize sediment going into the canal.
The intake structure will be fitted with six trash rack screens and a conveyor belt to clean the screens. On the left half of the river, two automated 40-ft. crest gates will be mounted to the river bottom, allowing floating debris to be flushed downstream in a safe manner.
"We're hopeful that our new facility will enable us to distribute irrigation water through the valley for another 100 years," Donald Barksdale, president of the Nampa and Meridian Irrigation District, said at the groundbreaking ceremony.
Crews also will install a screen designed to prevent adult fish from entering the canal, according to idahocapitalsun.com.
Greg Curtis, water superintendent of the Nampa and Meridian Irrigation District, said the project cost won't exceed $20.7 million, and crews hope to finish it by spring of 2027.
Construction work will be performed during the winter to avoid the summer river floating season at Barber Park, Curtis said. Work begins on one side of the river immediately and will continue until March or April. At that point, the old boards will be put back in the dam.
Construction work will resume on the river's other side in October 2026 and continue until completion.
(All photos courtesy of the Idaho Department of Water Resources.)
