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February 27, 2013

Duck River hybrid dam design work under way

Will be part earth-fill, part roller-compacted concrete

With Phase I excavation complete, city officials and engineers are now designing the proposed hybrid-style dam that will be built in the Duck River watershed.

The Cullman utilities board, with the cooperation of Cullman County and other area water systems, is creating a 640-acre lake with a 32-million-gallon-per-day capacity in northeast Cullman County. The dam will be approximately 2,000 feet wide.

The project is estimated to cost $68 million. Once complete it will be used in conjunction with the area’s sole water source Lake Catoma.

Phase I of construction and excavation is essentially complete with Birmingham-based contractor Brasfield & Gorrie. The next two phases will include dam and spillway construction and the raw water pipeline.

The project’s engineer of record CH2M Hill said geological modeling is well underway, as teams work to crunch site data acquired through excavations and drilling.

Engineers had originally planned to construct an earth-fill dam when the Army Corps. of Engineers permit was approved in the 1990s, though roller-compacted concrete became a more common and cost-effective option in the intervening years the project spent stalled due to lawsuits and political feuds.

Engineers briefly considered a fully roller-compacted concrete dam, but after studying the terrain, the decision was made for a  hybrid model featuring roller-compacted concrete at the center for the spillway with earth-fill components on the sides.

“The geology really dictates that, so it will be a part earth-fill and part-roller-compacted concrete dam,” Tom Harwell, with CH2M Hill, said. “You essentially have to fit the style of the dam to the geology of the site, and that’s what we’re doing.”

Officials say plans should be completed and the Phase 2 dam construction should be ready to bid out by the end of the year.

Owner’s representative Bill St. John has been tasked with much of the Phase III planning, which includes the approximately eight-mile pipeline from the reservoir to the water treatment plant. The proposed route will mostly run along U.S. Highway 278 east, though the city is negotiating with the Alabama Department of Transportation to determine exactly where the pipe will be laid.

“We’re showing two routes, one on the backside of the right of way and another down the ditch line, which we prefer,” St. John said. “It’s a price difference of about $800,000 (between the preferred route and second option), so if we can get them to let us put it in closer it could be a big cost savings. We’re putting an application together and we’ll be sending it soon.”

St. John’s office has also prepped a recreation plan for the restricted covenants under the permit, which outlines any recreational features the city might eventually build at the site. The plan covers walking trails, foot bridges, boat launch sites and a potential community education building. The plan only outlines potential options, none of which have actually been approved for construction.

“Some of these things may never happen, but you can never do them if you don’t put them in the plan now for down the line,” project coordinator Dale Greer said.

Trent Moore can be reached by e-mail at trentm@cullmantimes.com, or by telephone at 734-2131, ext. 220.

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