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Failed culvert, repairs cause weeklong detour on Idaho 55 near Marsing

Despite temperatures hovering near triple digits, Sunday began as a normal day for off-duty District 3 maintenance staff. Until mid-afternoon.

The afternoon tranquility was interrupted with a report that an irrigation culvert had failed, bringing failure to Idaho 55 that crossed over the culvert just west of Marsing. When crew members arrived, they discovered a portion of the highway had given way. By late afternoon, about two-thirds of the width of the road surface over the aged culvert had been compromised said Caldwell Maintenance Foreman Ken Crouch.

ITD closed the road to traffic at about 4:30 p.m.

Getting to the root of the problem required removal of the highway surface and all of the material between it and the 36-inch culvert (to a depth of about 20 feet) and removal of the corrugated pipe. In human years, the pipe was past retirement age.

The canal carries surplus irrigation water to the Snake River. For some reason, flow through the culvert was blocked, so the swollen canal, fed by an abnormally abundant water supply, made its own path around the culvert and under the highway.

Saturated soil had been creating soft spots for several weeks, Crouch said. Crews monitored it regularly, hoping the road and canal would make it through the irrigation season, thus avoiding an impact on water users. They fell a couple months short of reaching that goal, though.

It’s not clear whether the culvert had partially collapsed, causing the restriction, or whether accumulated debris might have been the culprit.

What initially was projected to be a two or three-day closure has extended to more than a week.

ITD maintenance crews created a diversion channel Tuesday and began preparing the trench for a new reinforced concrete culvert secured from a supplier in Nampa.

During the closure, Idaho 55 traffic destined for or coming from U.S. 95 was routed onto county roads, resulting in a detour of about two miles. An average of about 3,300 vehicles use the route daily.

Repair costs are estimated to be about $22,000.