Preliminary work is continuing on a spillway modification project at the emergency spillway at Pipestem Dam after an announcement that planning and design work had been funded by the U.S. Army Corps of Engineers, according to Chris Fassero, project manager for the corps.
Fassero said the project received $1.2 million in funding for the current fiscal year to continue the design work. Additional funding may be sought for 2020 with the intention of completing planning and design by the end of the 2020 calendar year.
For the rest of this fall, planning and design work will include two drill crews taking soil samples from the area behind the dam. The crews will continue drilling test holes until Nov. 9 or when winter weather closes down construction.
"They are taking core samples to bedrock and in some cases into the bedrock," Fassero said. "In some cases, they will install equipment to measure water within the holes."
The Corps of Engineers announced the plan to bolster the spillway at Pipestem in January. While water levels at Pipestem Dam have never reached the emergency spillway or caused safety concerns, a dam with a similar design at LaMoure, North Dakota, was damaged by high water in the spring of 2009.
The emergency spillway is located west of the paved road across the top of Pipestem Dam. Immediately south of the spillway is a broad relatively level area that had previously been used as a shooting range. From that area, there is a steeper slope with nearly a 90-foot vertical drop to Pipestem Creek below.
It is the area of the steeper drop that is at risk of eroding away because of layers of sand under the topsoil, Fassero said at the January meeting where corps officials announced the plans to local leaders. Erosion at that point could weaken the structure of the dam and pose a safety concern for downstream areas including Jamestown.
Fassero said 37th Street Southeast, a Midway Township road south of the back of the dam, may have to be rerouted, depending on how extensive the new spillway structure is. This fall's work includes survey and soil sample work south of the road.
The Corps of Engineers has approved but not funded the construction of the project at this time. Work could start in the spring of 2021 with actual construction taking four or five summers. Preliminary engineer's estimates are now about $200 million, Fassero said. That amount has increased from $175 million announced at the January meeting.
Fassero said the spillway modification project will not change the operations of the Pipestem Dam although lake levels may be temporarily lowered during some phases of construction.