Improving safety at the Third Street Dam
HURON – Placing large boulders below the Third Street dam would eliminate the deadly undertow while having a minimal impact on the James River water surface level, engineers with a Sioux Falls company said Thursday.
Stockwell Engineers has been retained to develop a James River Recreation Master Plan, and one of the first elements is to improve access to the river near the dam.
An “islands of the river” design theme as proposed will incorporate Crown Park, Memorial Park and Riverside Park in the plan.
About two dozen people attended an open house where engineers presented the Third Street dam proposal and answered questions.
Stockwell President Jon Brown said the dam is a small element of the master plan, but an important one.
“We had to understand what was happening on the river before we could come up with improvements up and down,” he said.
This early study phase is being funded by the city of Huron and the James River Water Development District.
Eliminating the undertow below the low-head dam – sometimes referred to as a “drowning machine” – is a major priority.
Communities around the country are working to remove similar dangerous conditions on rivers as they try to promote more water-related activities, Brown said.
“What we’re doing is a little bit different,” he said. “Some places they go in and they actually remove the dam itself and return the river back to its original state.
“We’re essentially doing the same thing by eliminating that undertow by just filling that area in with rocks, so in a sense creating a spillway through a ripple effect on the rocks,” Brown said.
He said they are trying to do it in as short a distance as possible between the dam and the bridge.
“Instead of water coming over the dam and creating an undertow, it will come over and ripple over the rocks,” he said.
The goal is to dissipate the energy with the rock while having as little impact on the water surface level as possible.
The situation is unique because the trestle, dam and bridge are so close together.
The velocity of the water will increase as it comes over the dam, however, it will return to a more normal rate at the bridge.
Brown said bridge inspections will have to be increased after construction to make sure the bridge isn’t affected.
There were audience questions about the impact of fishing and whether having the boulders in the water would entice kids to try to climb on them.
Brown said not all of the risks can be eliminated, but getting rid of the undertow will significantly reduce them. There are many studies that show that this can improve the situation with low-head dams, he said.
People could still get hurt, but someone who falls in the water near low-head dams and the undertow has no chance of pulling himself out, he said.
Stockwell plans to finalize construction plans by November. Construction will depend on available funding.