Click here to watch a photo showcase of Gavins Point Dam from last year to this year.
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On Wednesday, after the flows at Gavins Point Dam by Yankton, S.D., were zeroed out, workers squeegeed water off the concrete spillway and then ran mobile radar across it.
The radar checks the gravel subsurface for voids. While the results aren't yet known, the Army Corps of Engineers expects to find damage because it has already sent cameras down drainage holes in the spillway, according to corps spokesman Kevin Wingert.
The question, he said, is how much gravel and other material have been washed out from under the spillway. Repairs will be done this summer.
VIDEO: Maintenance at Gavins Point Dam