Canyon Lake project to replace spillway, dredge silt

2013-07-25T06:30:00Z 2013-07-25T14:28:15Z Canyon Lake project to replace spillway, dredge siltKevin Woster Journal staff Rapid City Journal
July 25, 2013 6:30 am  • 

Work will begin in September on a $3.7 million upgrade at Canyon Lake designed to rebuild the spillway, dredge portions of the lake bottom and add erosion-control structures on the shoreline.

The project was delayed in 2012 when only two bids were received and both were far over budget. The city got four bids this year and J. Scull Construction of Rapid City won the job at slightly more than $3.7 million.

Keith Johnson, the project administrator for the city, said delaying the project worked to the city's financial advantage.

"We bid it last year in July hoping to start in September. This year we opened bids in February," he said. "I think a lot of it was timing. We got the project bid this year for about a million less."

The work to begin after Labor Day is the second phase of a renovation project that began with construction of a bypass system to pipe inflows from Rapid Creek around the construction zone. The water will go into the canal-pond system in Canyon Lake Park and eventually back into the creek below.

That system was designed to prevent sediment in the lake from ending up in Rapid Creek below the dam, said Ev Hoyt, board member and past president of the Black Hills Flyfishers.

The flyfishing club contributed $20,000 to that initial work, hoping that the overall project would include extensive lake dredging. Club members might be a bit disappointed there, since only parts of the lake are scheduled to be dug out.

Johnson said the dredging will target the deeper parts of the lake near the dam, where most of the silt has accumulated since the last restoration work in 1995.

"We are going to dredge that lower portion from the spillway about to the first fishing pier around the corner," he said. "That's where most of the sediment is."

The contract calls for J. Scull to remove 12,000 cubic yards of silt, which is two or three feet deep in many areas. The lake, which covers 25 to 26 acres, is about eight feet deep at its deepest near the spillway, where dredging will improve depth.

There also will be some dredging near the lake inlet, where a cofferdam will be constructed as part of the work to divert Rapid Creek into the pipe system.

Hoyt has to admit, he wishes the sediment work were more extensive.

"I guess I don't know why you wouldn't dredge the whole lake," he said. "I hope they can do the whole thing."

The project is aimed at assuring the safety of the dam well into the future and preventing leaks from affecting water levels. A bentonite liner installed a few years ago has helped eliminate some leaks.

Rooster tails of water that alarmed visitors have been eliminated. Water still boils up in a spot below the spillway, indicating more work is needed.

"It wasn't considered a threat, but it did pretty much confirm that there was water running under the spillway, which you don't want," Johnson said.

The new spillway will be built in a configuration close to the current spillway. There might be a more decorative line and the concrete on the spillway might get some stain, Johnson said.

Erosion protection also will be added from the spillway and along the shoreline.

The first part of this phase of the restoration work will include lowering the Rapid Creek flows and the water levels in the lake. Ultimately the lake will be drained "pretty much completely," so machinery can get in to work on the structures and dig out silt, Johnson said.

"It will be pretty much dry from September to March," he said.

That means there could be another chance for area residents to see what lives in the lake. The draining of the much-smaller Memorial Pond for a project earlier this year required state Game, Fish & Parks Department fisheries crews to net and transplant a number of fish, including lunker northern pike, a big catfish and a large koi.

Even more fish are waiting in Canyon Lake. John Carreiro, a wildlife biologist for habitat and access with GF&P in Rapid City, said cooler temperatures will make fish work easier than it was at Memorial Pond.

The agency will monitor the water available to fish and act when needed, Carreiro said.

"If we need to get in there and get some of those fish out, we will," he said. "We could see some large northerns, some large trout and a variety of species. It'll be interesting." 

Contact Kevin Woster at 394-8413 or kevin.woster@rapidcityjournal.com

Copyright 2015 Rapid City Journal. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

(1) Comments

  1. Wishbone
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    Wishbone - July 31, 2013 2:08 pm
    For years I’ve considered Canyon Lake a burial ground. After the 1972 flood I saw the lake full of mud and imagined that among the paddle boats and boards, there might be bodies down there that had not been recovered. I hope J Scull Construction is sensitive to the fact that they may be dredging the same kinds of artifacts I find in Rapid Creek (all the time) – and more.
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