Becoming of the Sea

The U.S. Geological Survey recently published a map showing land area change in coastal Louisiana from 1932 – 2010; a more comprehensive survey than their previous efforts.   Using integrated data from historical surveys, landsat imagery, and national wetland inventories based on aerial photographs, their findings conclude that Louisiana has undergone a net change in land area of about -1,883 square miles.  From 1985 to 2010 the rate of land becoming ocean occurred at an average rate of one football field per hour.

[Leveed delta of the Mississippi (red = land loss, green = land creation).  “The spatial and temporal patterns observed reveal a dynamic landscape changing as a result of the complex and often interactive effects of natural and human-induced processes.”]

Although the survey’s findings confirm massive loss of land (90 percent of all U.S. wetland loss), significant land gain in the Atchafalaya Delta (below) is an obvious counterpoint to the overall trend.  Although the Mississippi is only allowed to have 30% of its flow pass through the Atchafalaya (the River tried to fully exploit that course for the next thousand years or so, but we had other plans), the Atchafalaya delta has effectively created about 30 square miles of land, most of it during the last 75 years of flood events during which the Morganza floodway was utilized.  Thus the floodway gates, which most of the time thwart the chosen course of the river, may also play the role of closest incidental analogue to the Mississippi’s former land fabrication tendencies, posing interesting questions given recent flood events and forthcoming data from the last month that didn’t make it into this survey.

Related: Marsh Terracing, Wetland Glyphs

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