Officials race against time to replace Boise canal pipe’s ‘catastrophic failure’
Ada County Highway District commissioners declared an emergency over a “catastrophic failure of a critical canal segment” that serves thousands of Boise residents. The agency is now in a race against time to repair a long-forgotten water pipe before irrigation water returns this spring.
A 48-inch corrugated metal pipe in the canal, located south of Hill Road and just west of North 32nd Street near the Hillside to Hollow Reserve, has “deteriorated far beyond its serviceable life,” an Ada County Highway District staff report stated.
“Critically, ACHD has over 50 direct storm drain connections upstream of the failure that rely on the canal to convey stormwater,” the report said. “Without a functioning canal, stormwater has nowhere to go.”
The district became aware of the issue on Sept. 15, when a representative of the Boise City Canal Co., which controls the canal, alerted the agency that the area was experiencing reduced water flow.
An inspection revealed that large portions of the pipe have rusted away, and tree root growth in that area caused blockages and parts of the pipe to cave inward, according to Matt Degen, Ada County Highway District safety engineer.
Degen told the Idaho Statesman that the agency had not previously been aware of a pipe’s existence. As employees have come and gone from the highway district over the years, this pipe “fell off the radar,” Degen said. A 1981 construction plan is the oldest documentation that staff was able to find that included the pipe, but they suspect it dates back even further.
“We don’t even really know how old it is,” Degen said by phone. “It’s at least four decades old. It’s even older than that. We don’t have the plans for it. It’s well beyond its useful life.”
The canal is a “vital conduit for irrigation” for thousands of Boise East End and North End residents, according to an ACHD report. As a precaution, Boise City Canal reduced irrigation water to residents, who mainly use it to water yards, Degen said.
Emergency declared to speed up replacement project
Officials are concerned that the degradation of the pipe could lead to potential flooding.
“Each day of delay increases the likelihood of storm events overwhelming the compromised system, resulting in property damage, public safety hazards, and costly emergency response,” the ACHD staff report stated.
Rain on Sept. 29 caused flooding upstream of the pipe failure, as well as on the nearest homeowner’s property, according to Rachel Bjornestad, highway district spokesperson. Maintenance crews had to use a vacuum truck to remove water from the area.
ACHD commissioners approved an emergency declaration on Oct. 1. The declaration will enable a faster funding and procurement process, allowing those overseeing the project to obtain the necessary materials as soon as possible, Degen said.
And time is ticking. Irrigation season will end around Oct. 15 in Boise, cutting off irrigation water until the spring. Degen said it’s vital that the pipe be replaced between then and March 15, the date that irrigation districts require canal work be completed before the irrigation season begins.
Under ideal circumstances, the project could be completed in 10 weeks, but weather delays are expected, according to an ACHD staff report.
Asked whether flooding in the area could threaten homes or roadways, Degen said it could potentially threaten both, but he is waiting for more information to know for certain. The engineer is not worried about damage in the short term, but he is concerned about future flood risks if the pipe isn’t replaced quickly.
“We’ve got to get this project going, because it’s not an easy project to build,” Degen said. “...We’re actually still in the design phase, because we just found out about this two weeks ago. But what (the emergency declaration) allows us to do is get a contractor on board and start ordering the necessary materials to get this thing fixed.”
Because of the pipe’s unique location at the base of a sandy slope, construction workers will need to install temporary supports to protect the hillside’s integrity as they make a 5-foot cut to remove and replace the pipe, according to Degen.
Ada County Highway District staff estimated the replacement project would cost more than $300,000, which would come out of the district’s 2026 Drainage Rehabilitation and Improvement Plan funds.
Traffic on adjacent roads could be minimally affected by the pipe repair, according to Degen.
The Boise City Canal Co. did not respond to the Statesman’s request for information.
This story was originally published October 8, 2025 at 9:57 AM.
