The Saratoga Sun -

By Mike Dunn 

Trouble over bridged water

 


Editor’s note: This is the second story in a series about the river restoration project on the Upper North Platte River. Next week’s story will discuss the financial issues.

By Mike Dunn

The Upper North Platte River physically divides the town. It divides the west part of the town from the east. It separates downtown from most of Carbon County.

People depend on the bridges in Saratoga. Not just for access to the other side of the town, but as a source for commerce and growth to the town as well.

The necessity of these bridges have several people concerned about how the Upper North Platte River Restoration Project will affect these structures and their stability.

Nathan Jean, of Stantec and project manager of the Upper North Platte River Restoration Project, said that the bridges will prove to be a difficult task for their project.

The Wyoming 130 bridge “is really at an upward skew of the river and that is going to be one of the big challenges as we go along is correcting that” Jean said. “The flow forces goes almost perpendicular to the value direction so its a skewed flow and its attacking, basically, the bridge piers which is why we are having some scour (removal of sediment) on those bridge piers. And also, that means that’s why you see that sediment bar. The bridge, because of its skew and the type of bridge that it is and the type of the piers that it has, it’s constricting some of the flow causing some backwater which is causing this sediment to build.”

In order to prevent bridge scour from occurring, the Stantec officials and Wildland Hydrology Consultants have developed several preliminary river structures and has a specific design in mind to help direct the flow of the river.

The structure that will most likely be used in order to preserve bridge stability is what is called a W-Weir Cross Frame. The goal of this structure is to decrease the stress the river flow has on the piers.

The goal of these structures are to make sure they are athletically pleasing, they look natural and they help with the long term impact of the river flow. There are several structures that may be used for the river to help impact the river flow and the bridge structure.

The flow over the structures will naturally create less stress and less scour over the bridge piers by designing what they call a “double W” design, which is essentially placing the W-Weir cross frames right next to each other. This will help guide the water safely between the piers.

Rosgen said that the challenge will be getting the absolutely correct angles to push the water between the piers.

The structure is planned to be set in accordance to the Highway 130 bridge which has seven piers. The pools are the areas of the lowest velocity and the highest depth of river flow.

The rocks used when creating these structures will most likely not create issues for boaters as they plan to be about one foot tall. Many boaters may actually enjoy the new structures.

“These (structures) are actually great for boating in the sense that you are going to have several lanes to take you down through there.” Brandon Rosgen of Wildlife Hydrology said, “A lot of people like to take their Kayaks through these areas.”

A second survey of the river will be completed this spring. The final plans for the river will be presented on June 21, 2014.

 

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