At Oaks/Avery, rock dikes held while the bay shore retreated

Along the Gulf Intracoastal Waterway, rock dikes helped hold the bank and catch sediment. Along nearby Vermilion Bay, marsh-grass plantings failed to stop the shoreline from retreating. Those contrasting results appear in Louisiana’s 2020 monitoring report for the Oaks/Avery Canals Hydrologic Restoration project, a coastal repair effort spanning parts of Vermilion and Iberia parishes. (CPRA, page 19)

The project covered 2,876 acres north of Vermilion Bay. Its waterways included Oaks Canal, Avery Canal and the Intracoastal Waterway, with Union Oil Canal marking part of the project’s eastern boundary. Rather than applying one treatment everywhere, the project paired grass planting on the bay shore with rock protection on waterway banks and structures intended to reduce rapid water-level changes within a marsh unit. (CPRA’s 2020 report, page 1)

According to the state report, roughly 34,000 smooth-cordgrass plants were planted along 5.1 miles of bay shoreline in summer 2000. Structural construction followed, and the $2.8 million project was completed in October 2002. The report described protecting 160 wetland acres over the project’s 20-year life as a projection, not a measured final result. (CPRA, page 2)

Monitoring showed where the investment worked. CPRA reported that the rock dikes captured sediment and helped the protected Intracoastal bank expand. The bay shoreline, however, continued to erode. Across the 2000–2018 monitoring period, the report recorded average retreat there of 3.1 meters a year. It concluded that the planted cordgrass had not spread enough to protect that shore. (CPRA, pages 19–20)

The work also required adjustments after construction. In 2012, crews repaired a breach and low sections along Oaks Canal and built an earthen plug across Union Canal. Part of that plug settled below its intended height after problems with the foundation and fill material. The same maintenance account says workers opened a gap in an existing rock plug to allow fish movement and installed a navigation aid at the new earthen plug. (CPRA’s 2020 report, page 6)

More rock was placed in 2019 to extend protection at the mouth of Oaks Canal and repair a subsided section of the Intracoastal dike, according to the report. The repair history shows that completing construction did not end the project’s maintenance needs. (CPRA, page 7)

The state’s account is a history of this project, not an inspection of its condition today. Its results also resist a simple verdict that restoration either worked or failed: rock protection met an erosion-control goal along the waterway, while the planted bay shore kept retreating. The contrast remains central to understanding what this particular investment accomplished. (CPRA’s 2020 report, page 19)