Drawing Louisiana's New Map Addressing Land Loss in Coastal Louisiana (2006) / Chapter Skim
Currently Skimming:
2 The Historic and Existing Louisiana Coastal Systems
2 The Historic and Existing Louisiana Coastal Systems
Pages 29-42
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From page 29... ...
sea level rise. Understanding these processes, and how human activity can alter them, is an important step in understanding and anticipating the evolution of a given delta.
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The Mississippi River Delta, one of the world's most extensively studied deltas, is composed of sediments from a catchment that covers much of the continental United States (3.2 million square kilometers [km2] or 1.2 million square miles [mi2]
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The alternation alongshore between areas of erosion and areas of accretion has produced a highly irregular shoreline and corresponding irregularities in the inner shelf contours. As pointed out in the programmatic environmental impact statement of the Louisiana Coastal Area (LCA)
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on coastal Louisiana land changes describes a complex mix of land losses and gains for this region, with land loss dominating. However, Roberts et al.
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External Changes to the Mississippi River Delta Beginning in the nineteenth century, dams were constructed along the Mississippi River and its tributaries to improve navigation, control floods, and provide water for irrigation and electric power generation (Meade, 1995)
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34 DRAWING LOUISIANA'S NEW MAP FIGURE 2.2 Annual discharge of suspended sediment at stations on the Missouri and Mississippi Rivers showing the effects of reservoirs on downstream sediment loads (19391982) (Meade and Parker, 1985; used with permission from the U.S.
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From page 35... ...
Relative sea level rise in much of the Louisiana coastal area is approximately one order of magnitude greater than the eustatic rate. A component of relative sea level rise is due to eustatic sea level rise.
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Instead, significant portions of sediment pass through the delta and accumulate on the outer continental shelf and in deeper waters of the Gulf of Mexico. The loss of this inorganic sediment from annual floods is a major underlying cause of land loss in coastal salt marshes experiencing rates of local, relative sea level rise up to 1 centimeter (cm)
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. NOTE: A crevasse splay is essentially a small-scale subdelta lobe; even though the time scale is shorter and the space scale is smaller, the same principles apply.
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(2000) claim that the influence of dredging on wetland loss varies spatially, and only 9 percent of the nondirect loss is due to altered hydrology and saltwater intrusion.
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Although the amount of land loss resulting directly from fluid withdrawal for oil and gas production is uncertain, there is a close spatial and temporal association between changes in petroleum field pressure reductions and land losses in nearby wetlands (Morton et al., 2002)
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Future Scenarios: Desirable Versus Attainable The ideal future condition of the Mississippi River Delta would be one that achieves the goal of Coast 2050: Toward a Sustainable Coastal Louisiana (Coast 2050) -- a sustainable "coastal ecosystem that supports and protects the environment, economy, and culture of southern Louisiana" (Louisiana Coastal Wetlands Conservation and Restoration Task Force and the Wetlands Conservation and Restoration Authority, 1998)
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Wetlands also promote flow reductions, which enhance nutrient removal and the deposition of organic and inorganic sediments. In the normal course of delta evolution, barrier islands move and eventually drown, and the marshes landward of them erode, supplementing the sediment supply for islands down-current through the alongshore drift.
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From page 42... ...
The extent of human activities and population growth in Louisiana has exacerbated land loss associated with natural processes and placed the current population and its infrastructure at risk from storms and land erosion. The natural and anthropogenic processes contributing to net land loss in coastal Louisiana are significant and pervasive and have been operating for decades.
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