Caernarvon Freshwater Diversion and Delta

Introduction

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Located 15 miles downriver from New Orleans in Plaquemines Parish near the Plaquemines/St. Bernard Parish line is the Caernarvon Freshwater Diversion. Constructed in 1991, the diversion was designed to divert up to 8,000 cubic feet per second, approximately the volume of 2,353 large crawfish pots each second. It's intended purpose was to move fresh river water from the Mississippi into the local estuary, limiting the capture of sediment. Despite this, new land is building in the diversion's main catch basin, Big Mar Pond. Although the diversion was not meant to transport sediment, the subsequent growth of land as a result of its opening resembles the activity of a sediment diversion. For that reason, understanding the effects of the Caernarvon Diversion on the surrounding basin may better inform the construction and operation of future diversions; an integral part of coastal restoration plans for the Southeast Louisiana. Investigating this emerging delta also offers an opportunity to observe and analyze land building processes as the result of a diversion. It is important to remember that a thriving delta with a restored swamp enhances hurricane storm surge protection to nearby levees and communities (see Multiple Lines of Defense Strategy.)

Images

Land changes in Big Mar

Backstory and Context

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Turbid, or murky, waters containing sediment have been depositing and developing into a delta complex within Big Mar. With the hope of better understanding the effect of future sediment diversions, we track the expansion and consolidation of this delta. We are beginning to expand these investigations outside of Big Mar and into the larger receiving basin, including any influence the diversion may have on the Breton Sound Basin.

To us, new land means more barriers between coastal communities and storm surge! And we can help ensure the longevity and stability of newly formed land by restoring the healthy swamp that once thrived there. That in itself is an intricate task, but luckily for us, the forming delta provides an outdoor laboratory, perfect for identifying best practices for swamp regeneration.

We plant species native to swamp environments, and continue to keep tabs on them in the following years, monitoring closely for survival and growth rates to inform future restoration projects. Since 2010, we have planted 25,594 trees and have restored more than 130 acres within Caernarvon receiving basin.