St. Vrain Diversion Structure Replacement

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Between 1932 and 2010 the state of Louisiana has lost about 2006 square miles of land due to a combination of subsidence, sea level rise, and management of the Mississippi River. Computer models predict a further loss of 1800 to 4200 square miles in the next 50 years, amounting to 55% of the land in Plaquemines Parish and resulting in $300 million in annual economic damage. Following hurricanes Katrina and Rita, the Coastal Protection and Restoration Authority (CPRA) was formed as a single state entity with the authority to protect and restore the lands of coastal Louisiana.

The $50 billion coastal master plan includes restoration and risk reduction projects. The restoration projects include barrier island restoration, hydrologic restoration, marsh creation, ridge restoration, sediment diversion, and shoreline protection. The Barataria and Breton Basins have experienced some of the largest land loss—almost 700 square miles. Two sediment diversions are being designed, one for each basin. The sediment diversions connect the Mississippi River to the basins, allowing for the controlled diversion of up to 75,000 cfs of water and sediment to the Barataria basin and 30,000 cfs to the Breton basin.

The design and construction of sediment diversions on the scale proposed for Barataria and Breton is unprecedented, the results of which will rely heavily on the numeric and physical modeling required to design the major diversion features, including the inlet, conveyance, and outlet structures. Alden is constructing two 1:65-scale, live-bed physical models to test performance and effectiveness of the diversions.

Discover more:

• Making Mississippi Mud In Massachusetts To Restore Wetlands | Here & Now [wbur.org]
• A Mini Mississippi In Mass. May Help Save New Orleans From Rising Seas [90.9 Boston NPR]
• Rerouting the Mississippi River could build new land—and save a retreating coast [Science Magazine]
• Find the Mississippi River in Massachusetts [Chronicle 5 WCVB]
• To Save Louisiana’s Vanishing Coast, Build a Mini Mississippi Near Boston [The New York Times nytimes.com]
• Louisiana researchers tackle a changing Mississippi Delta [PBS News Hour Weekend pbs.org]
• Mid-Barataria Sediment Diversion could create, save 47 square miles of land over 50 years [nola.com]
• CPRA Using Giant Model to Test Mid-Barataria Diversion
• Mississippi River Diversions Could Save Louisiana's Drowning Coast [enr.com]
• Louisiana Coastal Protection and Restoration Authority [Official Website]
• A Mini-Diversion in Boston is Paving the Way for Louisiana’s Boldest Coastal Project [mississippiriverdelta.org]

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The Cedar Cliff dam and hydropower project is located approximately six miles from Cullowhee, in Jackson Country, North Carolina. The dam and hydroelectric facility is owned by Duke Energy and is located downstream of three other hydroelectric projects that are operated as a system.

The primary spillway includes a Tainter gate and the existing auxiliary spillway system includes two fuse plug sections (with different crest/activation elevations).  It was determined that the combination of the primary and auxiliary spillway systems were not adequate to safely pass the regulatory-increased Inflow Design Flood (IDF). The construction of a Hydroplus Fusegate system with six semi-labyrinth Fusegates in an enlarged auxiliary spillway channel was selected to increase spillway capacity to safely pass the new IDF which is now the full Probable Maximum Flood (PMF). 

Two reduced scale physical models were constructed to determine the required size of a ventilation system for the proposed Cedar Cliff Fusegates and headpond and tailwater levels at each Fusegate for flows up to the sixth Fusegate activating. The tailwater levels were required for design of the Fusegate ballast system.  

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