Engineering for Dam Repairs | Design, Permitting and Construction Observation
Due to corrosion of an 11-foot diameter riveted steel penstock that extended through the earthen berm portion of the dam, the integrity of the earthen berm was jeopardized. This was evident from sink holes that had developed within the berm near the penstock. Verdantas' experience in geotechnical engineering and permitting and our ability to look at the “big picture” enabled us to perform simultaneous engineering evaluations, seepage mitigation design and permitting, as well as construction oversight and support during implementation of the work.
Achievements
IDENTIFIED SEEPAGE THROUGH THE EMBANKMENT AS THE CAUSE OF OBSERVED SINK HOLES – Verdantas performed a subsurface investigation through the dam embankment, and our observations of the embankment materials confirmed seepage as the primary cause of sink holes.
DESIGNED SEEPAGE MITIGATION – consisting of improving the dam embankment by installing a low permeability geosynthetic clay liner along with new rip rap armoring to prevent erosion and scour. Prepared design plans identifying the extent of improvements, required materials, construction methods, etc.
SUCCESSFULLY PERMITTED THE PROJECT THROUGH STATE AND FEDERAL AGENCIES – The project included obtaining the necessary permits (Massachusetts Chapter 253 Dam Safety Permit, Wetlands Protection Act permit and Notice of Intent, and Remediation General Permit for construction dewatering). In addition, Verdantas prepared an Emergency Action Plan for Construction Activities as required by the Chapter 253 permit.
OVERSAW CONSTRUCTION ACTIVITIES AND ADDRESSED PROJECT CHANGES AS ENCOUNTERED – Verdantas performed regular inspections of the construction activities to verify compliance with the design plans and permits. Construction efforts resulted in the need to modify the design as unexpected conditions were encountered, and Verdantascommunicated these changes to the owner and permitting agencies to maintain compliance and successfully complete the project.
Scope of Services
- Geotechnical Engineering
- Site Investigation
- Dam Embankment Seepage Analysis and Remedial Design
- State and Federal Permitting
- Construction Oversight
Client
IndustrialLocation
MACapability
Civil InfrastructureServices
Site EngineeringRelated Projects
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]

Civil Infrastructure
Mid-Barataria Sediment Diversion
Alden constructed two 1:65-scale, live-bed physical models to test performance and effectiveness of the proposed land rebuilding diversions on the Mississippi River.
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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Civil Infrastructure
Cedar Cliff Spillway
Physical model study to determine hydraulic performance of a proposed auxiliary spillway system during flooding events