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Websites: 18. Angert, Joe & Isaac Angert. Old River. Retrieved September 19, 2006, at http://users.stlcc.edu/jangert/oldriver/oldriver.html. These two authors have devoted their entire site to the Mississippi river, but the only helpful part was the description of Old River, the site of the locks that prevent the Mississippi river from completely converging with the Atchafalaya. If the change of course were allowed to occur, the existing MI channel in the lower basin would become a salt water estuary. Bayou Lafourche was the most recent MI river channel, before it switched to its present day configuration. The MI river would have switched channels when Henry Shreve dredged a shortened channel at Old River except for a large log jam blocking the head of the Atchafalaya. Today, there is about a 15 foot difference in the elevations of the MI and the Atchafalya rivers. In 1963, Congress mandated the construction of the Low Sill and Overbank structures to maintain the flow of the MI river into the Atchafalaya at about 30%. There is a good map of the valve structures at and around Old River. 19. Salley, Shawn W. Mississippi Embayment: The Quaternary Canvas. Retrieved September 19, 2006, from http://www.emporia.edu/earthsci/student/salley3/. This website explores the tectonic origin of the Mississippi river. When the super-continent Rodinia broke up, it formed smaller rift zones adjacent to the major rift that split off all of North America. The old rift zone was a down-warped basin and a natural course for a river, especially after the breakup of Pangaea induced sea level rise because of more glacial meltwater. Tectonic activity still occurs along these ancient faults, the New Madrid earthquakes of the early 1800s for example. Smaller, less notable quakes still happen today. The New Madrid fault is a remnant of the older Reelfoot Rift. Buried valleys show that the Teays river was once a major tributary of the Mississippi river. The present river valley is an example of a syncline, a fold structure where two sides slope together, concave upward and usually with younger rocks on the inside of the fold. There are great maps on this site: geologic, topographic, changing Gulf and Atlantic shorelines, hydrogeologic cross section of reiver bed, surface map of New Madrid fault zone, ancient Teays river, 3D view of river basin. 20. Wiener, James G., Calvin R. Fremling, Carl E. Korschegen, Kevin P. Kecow, Eileen M. Kirsch, Sara J. Rogers, Yao Yin, & Jennifer S. Saver. Mississippi River. Retrieved September 19, 2006, from http://biology.usgsg.gov/s+t/SNT/noframe/ms137.htm/. This website describes the geography of the river in great detail, highlighting the important tributaries and, in somewhat less detail, distributaries. It divides the river into and upper and lower basin, using the point where the Ohio enters the Mississippi as the dividing point. Levees prevent the continued buildup of the barrier islands which serve two functions: providing resistance/friction to incoming storms, preventing too much saltwater from entering brackish and freshwater marshes. This site includes a few political maps of the river and its tributaries. It emphasizes the importance of glaciers in digging the river channel, especially in the upper basin, where the channel includes some extinct glacial lakes. Construction of large dams in the 1950s and 60s along the Missouri created deep, cold water reservoirs that trap sediment, reducing the load of the Missouri, the principle sediment supplier to the Mississippi, by about 70%. The other main tributaries of the Mississippi include the Black, Texas, Yazoo, Big Sunflower, and St. Francis rivers. The load of fine silt ad clay picked up just above New Orleans prevents the river meandering too much further down and deepens and narrows the channel. The current diversion of the Mississippi through the Atchafalaya river and Lake Ponchartrain decrease up to 2/3 of floods around Baton Rouge and New Orleans. 21. (several). Times Picayune:Katrina Report. Retrieved September 20, 2006, at http://www.nola.com/katrina/graphics. This is part of the Katrina site the local New Orleans newspaper, the Times Picayune. I used the URL for the graphics page because the drawings and maps of the city, river, delta, levee systems, and lakes are very clear and easy to understand. Each picture is also put into context of the first page of the article that it originally accompanied. The newspaper has not edited the graphics at all; rather, they have included every graphic somehow related to the hurricane since it hit last August. This provides a timeline of events in new Orleans: from the initial devastation, to tentative explanations of the protection system failure, to the most immediate rebuilding efforts, to more detailed investigations and reviews of the original plans and planners (mostly the Corps), to the current political situation in New Orleans and how it will choose to organize the “new” city. Besides graphics and articles, this site also provides a meticulous documentation of the correspondences (emails, calls, letters, notes) submitted by Governor Blanco to the congressional hearing concerning Katrina. |