HARRISBURG, S.D. — The spillway at Lake Alvin is inching closer to a much-needed replacement after back-to-back years of unusual rainfall and flooding caused damage to the structure.
During Friday’s meeting of the South Dakota Game, Fish and Parks (GFP) Commission, department staff provided commissioners with an update on dam replacement projects years in the making on opposite ends of the state.
While a structure replacement project at Newell Lake in northwestern South Dakota is well underway, work at Lake Alvin — more than 400 miles away to the east of Harrisburg — remains in the planning stages.
Formed by damming Nine Mile Creek in 1954, Lake Alvin sits elevated above the Big Sioux River. After 40 years of use, the spillway was replaced in 1994. More than two decades later, heavy rainfalls in 2018 and 2019 saw the lake rise by multiple feet, which led to serious flooding of the 105-acre lake that damaged the already-aging structure.
Very heavy rain fell along Interstate 90 in Minnesota into southeast SD. The rainfall that occurred at the Sioux Falls airport was the 5th highest two day total on record for any month! pic.twitter.com/7OC0hfHYom
— NWS Sioux Falls (@NWSSiouxFalls) June 21, 2018
According to GFP planning and development administrator Adam Kulesa, the sheer amount of water in Lake Alvin those years led to the failure of embankments on both sides of the dam, paired with the failure or partial-failure of cement walls on the edge of the spillway. The damages undermined the integrity of the structure, he said.
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“Back in 2019 we had some damage, and that started the process with FEMA,” Kulesa said, “and the ultimate decision — instead of taking that money for repair — that we’d take that money and put it toward a replacement project.”
The GFP estimates that a full replacement would cost anywhere between $4.4 million to $5.6 million, with an additional $400,000 budgeted for design and oversight.
Because of a disaster declaration, FEMA funds will cover 75% of the cost to restore the dam to pre-damage condition. Additional costs associated with replacement instead of repair will fall on the state.
Kulesa said that, fortunately for the project, a 2022 legislative appropriation for replacements at Lake Alvin and Newell Lake will help fund costs beyond FEMA assistance.
“Senate Bill 67 provided a really needed shot in the arm for us at $5.6 million to put toward these two projects so we can see them to completion and have facilities that can be enjoyed for decades to come,” he said.
The spillway, which has previously been a flatter, concrete chute, is expected to be replaced with a stepped-spillway, which Kulesa explained will help reduce the force of the thousands of gallons of water spilling over the dam.
“The style comes down to water pressure dissipation and the dissipation of all that energy,” Kulesa said. “With these design methods are engineered to slow that amount of pressure coming off the lake and alleviate the pressure on more of those downstream types of things by dissipating that energy.”
Kulesa told the GFP Commission that work on Lake Alvin’s spillway is expected to begin in the fall of 2023, with completion anticipated before the spring runoff in 2024.
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After his briefing, Commission Chair Stephanie Rissler asked Kulesa about what impact the construction may have on any of the 27,000 visitors that GFP says visit Lake Alvin each year. Kulesa told Rissler that the lake will have to be drawn down somewhat, but that impacts to visitors should be minimal.
In a phone call with Sioux Falls Live, Kulesa said that the GFP will likely hold public meetings in Lincoln County to answer questions from residents and guests about what to expect with the project.
“Sometimes with projects like these we get a lot of local concerns … and rumors flowing around,” Kulesa said, citing past interactions he’s had. “We want to be transparent and up-front about what we’re doing [at Lake Alvin].”
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