A stretch of Ann Arbor's Border-to-Border Trail near Gallup Park is closed with no reopening date after city crews found a sinkhole caused by deteriorating underground pipes.

The closed section runs between the Geddes Dam and the Gallup Park fishing pond along the Huron River. Ann Arbor's parks department first shut the path to pedestrians and cyclists earlier in September. In an update Tuesday, Sept. 15, the department confirmed the closure is indefinite.

The problem traces to three stormwater culverts buried beneath the trail that connect South Pond to the Huron River. City staff discovered a sinkhole above one of the culverts in July and found that deteriorating pipes were letting soil migrate inside, hollowing out the ground under the trail surface, MLive reported.

Metal extensions on two of the culverts date to the 1960s and have reached the end of their useful life, the parks department said. More sinkholes and surface instability are possible.

The affected stretch was repaved and widened in 2017 as part of a mile-long improvement between the Geddes Dam and the Universal Access Playground, according to the city's Gallup Park page. Less than a decade later, the aging infrastructure beneath that surface is failing.

The city is hiring an engineering firm to evaluate temporary fixes that could reopen the trail while a permanent repair is designed. No timeline for either step has been announced.

The closure cuts through one of the trail's busiest corridors. Gallup Park is a 69-acre site the city calls Ann Arbor's most popular recreation area. The Border-to-Border Trail stretches 55 miles across Washtenaw County, with nearly 43 miles completed, according to the trails website.

Roy Townsend, project manager for the Washtenaw County Parks and Recreation Commission, said in an August interview on WEMU that some B2B segments draw 400,000 to 600,000 users a year.

The parks department said it appreciates the community's patience as it works to restore the trail connection. No detour route for walkers or cyclists has been posted.

Residents can check the city's Gallup Park page for updates on the closure.