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Articles: 9. Barkau, Robert L. (2000). Impact of Levees on the Middle Mississippi River. In Frazier, Ann G. & Gary E. Freedman, Selected Studies on Natural and Human Factors Related to Flood Management in the Upper Mississippi River Basin. Reston, VA: United States Geological Society. This article compares various situations for the river settlements along the upper and middle Mississippi river basin: flood/no flood, levees/levee failure/no levees, Pick-Sloan floodway/SAST floodway. The outcome of the studeies is depended mainly on the flow rate and volume of water, rather than the geology of the channel and surround area. This may be helpful in designing a model of the river. It could help decide which tributaries and distributaries are most important to include, how much friction to create on the surface of the channel, as well as creating general elevation models for the surrounding areas. 10. Coleman, James M. & H. H. Roberts. (1990). Transactions of the 40th Annual Meeting of the Gulf Coast Association of Geological Societies. Shapes and Sizes of Reservoir Sand Bodies-A Bird’s Eye View of Modern Mississippi Delta. Volume 40, pp131-133. Lafayette, Lousisana: Gulf Coast Associaion of Geological Societies. This article describes the sand depositional features that generally become oil or gas reservoirs in the river’s delta: fluvial channel fill, bay fill, distributary channel fill, distributary mouth bar, delta front environments. Sand deposits have cross-bedding and alternating well and poorly sorted bedding. Many have several reservoir units within one formation, depending on the porosity and permeability of the sediment. Channel fill happens when a distributary channel is abandoned, often suddenly (log jam, high flood, hurricane) or more slowly (loss of channel gradient over time). These sand deposits are full of organic particles and hardly ever exhibit graded bedding. In bay fill, break from a major distributary channel is made during a flood. Over a short time, the new channel reaches its peak discharge, then eventually becomes extinct. While the river was pouring part of its volume through the channel, the bay that the channel emptied into temporarily became a marsh. After the channel becomes extinct, the area reverts to a marine bay, but with a layer of river and marsh sediment on the bottom. Bay deposits are sorted vertically, with particles becoming coarser and layers thicker as you go up to the surface. Here, then oil and gas deposits are often separated vertically. There are also many oil and gas reserves near the front of the delta. Because of the graded bedding that is common in this area, these reserves tend to have the greatest horizontal continuity. There are three types of main distributary channel patterns: single (bell delta), rejoining, and bifurcating (delta with many complex channels, like the Mississippi). 11. Dean, Cornelia. (2006, September). Time to Move the Mississippi, Experts Say. The New York Times: Science Times, pp. D1, D4. The article examines the prospect of diverting the Mississippi river below New Orleans. This would eliminate only smaller towns, such as Empire, Venice, and Pilottown, and minimize relocation of people. The Mississippi river now carries less than one-half the sediment that it used to, largely because of large reservoirs built on the Missouri and Arkansas rivers, which are major tributaries. This diversion may help eliminate the dead zone near the mouth of the river in the Gulf of Mexico, by sending the excess nutrients that come down the river into marshes and swamps, where they may encourage healthy plant growth. Louisiana authorities are calling a meeting of experts and engineers from around the world, including representatives from the Army Corps of Engineers and river specialists from Tulane University, to decide how to “fix” the river in the long-term. This article also has three helpful, color maps. 12. Kesel, Richard H. The Role of the Mississippi River in Wetland Loss in Southeastern Louisiana, USA. Environmental and Geological Water Science, 13 no. 3, 183-193. Wetlands are built up by deposition on a delta or redistribution of sediment along coast by marine waves and currents. The article also includes a brief description of the suspended (mostly fine sand, also silt and clay) and bed load (coarser materials) of the Mississippi river in particular. The suspended load of the river is decreasing drastically, mostly because of damns and reservoirs built on the Missouri and Arkansas rivers. A decrease in the average size of suspended particles has also been observed. This article also talks about crevasses or crevasse sprays (when a natural levee is breached upstream of the delta) and sub-deltas (when a natural levee is breached at the mouth or on the delta). These breaches generally develop along the concave bank of meanders, where they current is the strongest. Crevasses are often only filled with water during a flood period, whereas a sub-delta has a more continuous flow. Sub-deltas also have a lower sediment retention rate than crevasse sprays because of tides, waves, and ocean currents that act on it. Both kinds are major contributors to land build-up at the mouth and along the banks of the river. Spillways are man-made and controlled crevasses to protect people and cities form floods (the Bonnet-Carre that protects New Orleans for example). Spillways may be designed to redistribute sediment to struggling wetlands? 13. Kim, Wonsuck, Chris Paola, Vaughan R. Voller, & John B. Swenson. (2005). Experimental Measurement of the Relative Importance of Controls on Shoreline Migration. Controls on Shoreline Migration. Retrieved September 20, 2006, from http://www.geo.umn.edu/orgs/seds/Sedi_Research.htm. This group of researchers used a model of a subsiding river basin to determine which factors: eustatic sea level, subsidence, or sediment supply rates (collectively the stratigrahic trinity) is most important in shoreline migration. They tried to simulate conditions of the Mississippi delta. The experimenters set the base (sea) level as the independent variable and determined that with all the above listed measured values, they could predict shoreline migration very accurately. Loss of prediction accuracy as each variable is replaced by an average or estimate determines how important it is to measure that particular value in order to make an accurate prediction. They found that vase level is the most important factor, followed by sediment supply rates and subsidence. 14. Kolb, & Van Lopik. (1966). Depositional Environments of the Mississippi River Deltaic Plain. In Martha Lou Shirley, Deltas in their Geologic Framework. Houston, Texas: Houston Geological Society. This article is mainly useful because of the excellent maps and tables of previous deltas and courses that the river took, including the ages and duration of each period. There are maps of marsh, swamp, lacustrine (lake), and beach deposits. There is also a great explanation of each of the sediment layers in the Mississippi delta. This article does not include anything about why the river changes course or where the sediment originates. It also does not examine the engineering aspects of how humans might and have tried to control the river. 15. Rainwater. (1966). The Geologic Importance of Deltas. In Martha Lou Shirley, Deltas in their Geologic Framework. Houston, Texas: Houston Geological Society. This author mostly talks about how oil and gas reserves formed in the former deltas. Large deltas with a fast sedimentation rate and high organic content, like the Mississippi river are ideal for building oil and gas deposits. Structural movements such as anticlines, domes, and faults, all of which are found the Gulf of Mexico near the river’s mouth, help concentrate gas deposits. This article includes a useful chart of delta sediment layers. |