Envirocon recently completed the removal of two historic dams in the Southeastern United States, allowing a two-mile stretch of river to flow freely over native bedrock for the first time in over 100 years. The remote river posed various challenges that required Envirocon to develop and implement innovative construction and demolition methods to successfully perform the dam removal.
Faced with a challenge to quickly lower water levels behind Dam 1 for hydraulic dredging to begin, Envirocon designed and installed three siphons to lower the pool elevation behind the dam. The siphons continued to control pool elevation after the dredging was complete, allowing Envirocon to build an access road and causeway on the upstream side of the dam. The siphons proved to be an innovative and cost-effective solution performing key functions necessary to the successful removal of Dam 1. These functions included quickly lowering the pool elevation so the hydraulic dredges could reach the bedrock and matching flow rates in a river prone to flash flooding, which negated any potential disruption in the construction of access roads and causeways.
Dam 2 posed a separate set of challenges to create access for dredging behind the dam. A steep, narrow, one-lane road leading to a powerhouse on the downstream side of the dam made mobilizing the site with equipment particularly difficult. Due to these limited access issues, Envirocon implemented a solution that required demolition of the powerhouse to build a crane pad to position a 350-ton crane.
What came next required a creative approach to solve the access issue. The crane was used to lift and place necessary machinery upon floats in the upstream pool behind the dam. These floats would ultimately be pinned together and equipped with a crane mat to make room for the 80,000 lb long reach excavator. The long reach excavator was lifted above the river by the crane and set in place on top of the floats. Once in place on the floats, the long reach excavator dredged to the bedrock in front of the existing sluice gates to allow for pool elevation control.
Next, the long reach excavator was replaced with a 40,000 lb excavator equipped with a breaker in order for dam demolition to begin. The excavator was also lifted in by crane into position on top of the floats inside the river. Once the spillway elevation was lowered to a sufficient level, the floating equipment was removed. Demolition proceeded from the downstream side of the dam using the crane pad material and Dam 1 demo debris to construct access roads and ramps. The dam was removed to its native bedrock and the river was restored to match its original slopes, including removal of the access road.
With the completion of the 11-month project, Envirocon marked its third successful major dam removal this year. While each project poses unique challenges, Envirocon continues its commitment to providing cost-effective solutions to complex river restoration projects.