Shawmut Hydro Dam

Bancroft Contracting Corporation in conjunction with Kleinschmidt USA, designed and constructed a rubber bladder flashboard system for NextEra Energy on the Shawmut Dam at Shawmut Village on the Kennebec River.  The finished design called for three separate 240-foot long rubber bladders, spanning the entire length of the dam crest.

The project required removal of an existing steel-pin and plywood flashboard system as well as approximately 155 cubic yards of existing concrete on the 750-foot long spillway of the Shawmut Dam.  Bancroft Contracting crews installed approximately 1,500 cubic yards of replacement crest concrete, embedding bladder-system anchoring hardware as required.  The project required construction of two 40-cubic-yard, 10-foot high concrete piers, separating the crest into three 240-foot sections to allow installation of the three bladders.  Bancroft erected a pre-engineered steel control house, air pumps, associated controls and extensive stainless steel air-piping to allow operation of the new bladder system. Finally, Bancroft installed the three 250-foot long 4.3-foot high air-inflatable rubber bladders on the dam crest.

Project Manager for NextEra was Paul Plante, Bancroft Contracting Corporation was general contractor, represented by Project Manager Allan Howe, and on site by Superintendent Mario DeMillo.  Engineering was by Kleinschmidt USA, represented by Steve Ruell.

Contribution to the Community

The Shawmut Dam crest renovations project makes its most important contribution to the community by increasing the efficiency of the NextEra Energy Shawmut Station as a source of clean hydroelectric power.  Maine’s electric power needs are currently met in largest part  by power generated from burning natural gas and imported oil.  This project permits NextEra operators to control the crest height remotely and under any water conditions.  This ability assures maximal utilization of available water flow even during and immediately following seasonal and other high-water events.  Because of this project, the Shawmut Dam is a more efficient source of clean, locally produced electric power that lessens the community’s reliance on imported fossil fuels with their attendant carbon outputs, increasing cost, and potential availability issues.

The crest renovations also contribute significantly to safety of the site operators by allowing them to control dam crest height by the operation of remote controls, rather than by direct access to the crest itself.

Job Challenges & Innovation

Water control for the duration of the project presented one of the most difficult challenges.   Frequent high water events on the Kennebec River prevented access to various work locations on the dam crest at unpredictable times. In order to maintain progress on the project, it was necessary to change work locations on the dam frequently, and to maintain a flexible approach to the construction plan.

Installation of crest concrete proved another challenge.  Distance and site topography made it impossible to pump concrete to most locations along the 750-foot crest.  Bancroft responded to this challenge by ordering seven-yard loads of concrete and transporting them to the dam crest by barge in 1-yard concrete hoppers.  Bancroft crews then used a barge-mounted crane to place the concrete one yard at a time.  The use of seven-yard loads of concrete allowed Bancroft crews to complete placements within the 1 ½ hour window allowed by the project specifications.

Environmental

The Shawmut Dam crest renovations project was carried to completion without adverse environmental impact.  The project waste stream was contained and appropriately disposed.  Impacts to water and air were minimal or non-existent.

The project has positive environmental impact in that it will permit this important Maine hydro site to produce clean, renewable electric energy at peak efficiency.

Response to Client Needs

Bancroft Contracting Corporation together with Kleinschmidt USA provided NextEra with a complete design-build crest renovation package.  During the progress of the project, Bancroft engineered and installed a crest-mounted bulkhead that allowed Bancroft crews to work efficiently despite high-water levels.  This bulkhead was a critical factor in allowing Bancroft to complete the project within the intended schedule.

Bancroft’s flexible approach to the construction schedule kept the crew productive during periods of high water and allowed Bancroft to complete the project on schedule.

Safety

Relying on workplace safety practices and the “zero accidents” culture developed and practiced over years at both NextEra Energy and Bancroft Contracting allowed Bancroft crews to complete this high-risk, two-year project with zero incidents and zero injuries. The Shawmut Dam Crest Renovation project began and ended with no daylight between owner and contractor with respect to the priority placed on worker safety.

Credit for this accomplishment belongs in several places:  NextEra has always made it clear that production never takes precedence over safety on their projects.    Project Manager Allan Howe and Superintendent  Mario DeMillo provided effective safety leadership for the duration of the project.  However, the lion’s share of the credit for this outstanding safety accomplishment goes to the Bancroft crew.  These trained and seasoned construction professionals worked under demanding conditions without compromise to safe work practices, producing safety results for the Shawmut Dam project second to none in the industry.