Workers are taking advantage of frozen ground winter 2018 to repair and reinforce the weir at Willow Pond at Matthaei Botanical Gardens. (A weir is a structure across a river or body of water that alters the flow of the water and usually results in a change in the water level.) “We first noticed a sinkhole developing on the west side of the Willow Pond bridge,” says Field Services Manager Jeff Plakke. Underground water flow around the west side of the weir was causing the trail to gradually cave in, he explains. “Initially volunteers built a sturdy ramp over the soft ground to prevent someone stepping through the softening ground. It was at this point we began the planning process that eventually lead to the work that’s happening now.”
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During the 2016 growing season thesoft spot gave way and a large hole opened up under the ramp. “In 2017 the ramp was extended and we worked to slow the erosion by building a sandbag wall to reduce the stormwater flowing around the weir,” Jeff says. This was somewhat effective, but water was still finding its way under ground and around the weir. The project underway now consists of removing the wooden bridge that sits on the weir, repairing the weir with sheet pile and concrete, then placing the original bridge back on the weir.
Despite the cold, winter is a good time to conduct a project like this. The ground is frozen so there’s less concern about disturbing the soil and plants with the heavy machinery necessary to do a job like this. Winter is also a time when most animals, birds, insects, and plants are dormant.