Marsh Terracing, Wetland Glyphs

Looking at the U.S. Gulf Coast at a distance of approximately 35,000 ft from its surface reveals a labyrinth of sinuous river deltas bifurcated by a network of short-circuiting canals and roadways.  Changes in water flow patterns caused by the canals and other engineering efforts have unintentionally created one of the world’s fastest eroding landscapes – a massive geological erasure.  Coastal Louisiana alone accounts for 80 percent of all land loss in the United States.

As all this verdant, aqueous land morphs into relatively vacuous sea, a third mediating system has appeared known as marsh terracing.  Looking like archaic glyphs or infrastructure for speculative urban development (…which in many ways they are), marsh terracing is a reclamation tactic used to restore coastal wetlands by converting shallow open pools into constructed arrays of intertidal marsh.

The terraces are built with earthen material imported from somewhere else – most likely the very same dredged sediment displaced from its former productive destination by the system of levees and canals.  Like a human do-it-yourself geo-circuit, marsh terracing uses strategic placement of accreted material to initiate more accretion.  The earth berms create a gradient of habitats encouraging further recruitment by sediment, plants, fish and other agents.  Rather than remove the system of canals (a highly improbable option), marsh terracing attempts to counter their effects by adding further anthro-constructions to the system.

Marsh terracing isn’t new technology per se.  Rather its just gotten more industrially scaled – like a contemporary adoption of the chinampa used within a much more dynamic and challenging landscape.  The forms of the terraced grids vary according to current techniques and site conditions, such as local patterns of tidal currents and wind direction.

If you look around on Google Earth you can stumble upon these operative symbols, and in some cases (like the image above) see the earthworks in the midst of being manufactured.

As the use of this technique in the gulf coast is in its infancy, we wonder how they will evolve and how they might be improved.  What else could be programmed into them?  What else might be farmed here?  One idea currently in development is a type of sacrificial (…or perhaps intentionally remedial?)  ring of wetlands to buffer future mishaps occurring within the gulf’s extensive oil extraction ecology.

[Military vehicles dump material as they build a berm across an opening in the beach just west of Grand Isle on May 10 (2010) in an effort to protect marsh lands.  Source.   “This is a second-tier defense system, where we would go somewhat inland of marshes where oil has been spotted, either a few feet or a few yards, and develop a more robust oil barrier…In some cases, we’d be establishing a sacrificial marsh area, but also blocking oil from getting even further inland into the marsh.“]

Louisiana has the highest coastal wetlands loss rate of any state in the nation comprising more than 1,500 square miles of marsh over the past seven decades. Coastal marshes have been deteriorating since man-made navigation channels changed the natural water-flow patterns on the landscape, allowing saltwater to intrude into areas of the marsh where vegetation is less tolerant of high salinity. When this happens, the stressed vegetation dies, which creates large areas of shallow open water and broken marsh. These open-water areas are characterized by relatively unproductive turbid water void of any submersed aquatic vegetation. Marshes adjacent to these large open-water areas are currently experiencing severe erosion caused by wind-generated waves. Twenty-five to thirty-five square miles of the coast’s emergent wetlands are being replaced every year by open-water habitats.

Tags: Land Loss, Marsh Terracing