Union County limits erosion at Lake Surprise

When Lake Surprise was dredged a decade ago, the last thing anyone wanted, was for sediment to clog the 24-acre lake again — or at least any time soon. So as part
of an effort to slow down the forces of nature in Union County’s Watchung Reservation, the county launched a major project late last year targeting the ravines where rain water rushes down to the lake.
“We spent $1.3 million taking sediment out of Lake Surprise. We didn’t want to be back doing it anytime soon,” said Alfred Faella, who heads the county’s parks department.
Most of the funding for the dredging in 2000 came from the state as part of the compensation to the county for the parkland required to complete Route 78.
Lake Surprise was created in the mid-1800s through the damming of the Blue Brook. The lake served as a reservoir to ensure sufficient water power to a mill downstream, west of the lake.
Nestled between the First and Second Watchung Mountain ranges, more than 1,000 acres of hilly terrain drain into the lake, which also marks the boundary line between Mountainside and Summit. When heavy rains roll through the region, the water run-off from some of the steeper slopes carries the well-worn soil down to the lake.
So the county brought in engineering consultants to identify the most serious locations where sediment was washing down to the lake and design measures to slow or stop those erosive forces, Faella said. There are now rock-lined channels at five different locations along the lake.
“Because of the slopes involved, you need to armor these ravines to prevent them from being torn up,” Faella said.
In some cases, rip rap rock was set in place, while in others, gabions or layers of rock wired together in a cage, were used. Unlike the gabions seen along interstate highways in falling rock zones that are shaped like hay bales, these gabions were designed more like mattresses, shallow, but very wide.

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