Lake Tecumseh Weir
BackgroundLake Tecumseh is a shallow 261 acre lake located next to the Atlantic Ocean in Virginia Beach, Virginia. It is connected to Back Bay estuary, which feeds into the ocean via the Asheville Bridge Canal. The US Fish and Wildlife Service chose to focus its resources on improving these bodies of water to ensure local species would thrive. For decades, wave action within the shallow lake stirred bottom sediments, eroding shorelines and causing water level fluctuation. Sediments traveled from the lake into the neighboring estuary compromising aquatic vegetation, local fish species and bird habitats.
Project ScopeEngineers set out to design two separate structures. First, a weir constructed of two walls anchored together was designed to control water level fluctuations and sediment transfer. The 40 foot long weir would anchor an additional 15 feet into the bank on each side to protect against seepage and erosion. The second structure would help to rehabilitate the earthen berm that had suffered from severe erosion over the years. US Fish and Wildlife needed a product with superior UV protection as well as a product that was impervious to severe rodent damage. Steel and treated wood were not an option as these traditional materials would rust and/or leech chemicals into the waterway. Concrete was also dismissed as the saltwater would breakdown the structure before the desired design life was reached. ShoreGuard vinyl sheet piling was chosen as the ideal material to address the design requirements for both structures. Vinyl’s lightweight nature requires less equipment, increases installation speed and reduces the environmental impact of construction. ShoreGuard’s proven performance in hundreds of past projects involving the US Fish and Wildlife Service and the US Army Corps of Engineers helped streamline the plan approval process. ShoreGuard’s advanced manufacturing process, XCR Technology, offered many additional benefits over other materials.
PerformanceThe Lake Tecumseh weir extends 1.0 foot above sea level exposing the structure fall through spring but submerging it during summer months when high tide reaches 1.5 feet. Prior to the project, studies indicated that over 2,000 tons of sediment were discharged annually from the lake. US Fish and Wildlife studies show that the spillway reduces 90% of the sediment from reaching Back Bay estuary. The stable water levels have helped to repopulate fish and aquatic vegetation species as well as attract wading birds and waterfowl. An added advantage of the ShoreGuard weir and stable water level is that boating activities are now possible on Lake Tecumseh an additional 190 days each year.
ConstructionTo protect the area’s natural habitat, a preparation area for equipment and materials was set up a half a mile from the installation site. The contractor’s steel barge transported supplies, crew and machinery back and forth as needed. The two 40 foot walls, anchored to each other were constructed using 24 foot long ShoreGuard 625 sheet piling installed by an excavator using vibratory plate compactor. The weir wall transitioned into the berm support, also constructed with ShoreGuard sheet piling. For this section of the project, 8 foot long ShoreGuard 325 panels were driven 6 feet into the earthen dam and help prevent further erosion.
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