re: What are these (South Louisiana)

If built in the right place. It's a very passive management/restoration process that relies on sediment flow/settling.

The idea is that the terraces will capture sediment and cause it to settle. This eventually builds up the marsh bottom, and with the sediment settling out of the water column, sunlight is able to reach the marsh bottom and allow vegetation to grow. The terrace fields are built such that they are oriented with the predominant winds for that area. The straightline terraces were designed as a grid, while the newer "duck wing" terraces are staggered and "inverted" so that sediment is trapped between the rows.

The terraces I have seen personally have definitely accomplished the sediment capturing part of the plan, but only those in high sediment flow areas. If you have very little sediment in the water column, it could take decades to see measurable results. It may take decades for vegetation to start spreading in between the terraces.

Material used to build the terraces is critical to the success. I've seen some built put of marsh "soils", and the amount of organic matter in the soil allows water in, and the terraces erode away in a matter of years. The strongest ones are made of very dense clay, and will take decades to erode, even if left unvegetated. The problem is, planting these is difficult, and the plants spresd very little because of how dense the clay is.

The best ones are a clay loam...strong enough to withstand wind and wave action, but allows vegetation to spread.

Almost every terrace project includes plantings. The sides are often planted with cordgrass to stabilize them and introduce a seed source for future growth.

Terraces also provide pretty good mottled duck nesting habitat.