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BESC 320- River Sills

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Kaitlin Akard

on 26 April 2013

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Transcript of BESC 320- River Sills

Kaitlin Akard, Enoch Chan, Tim Erickson, Mark Middlebrooks River Sills Sill: "a submerged ridge at a relatively shallow depth separating the basins of two bodies of water."
Used to prevent
mixing of fresh water flows
entry of salt water into fresh water channels
Construction materials
dredged sediment
imported rock/stone
concrete River Sills Canals on riverbed bottoms allow for salt water to creep upstream
Salt water is more dense than fresh water
For the Mississippi River, channel deepening is the main cause of salt water intrusion
Can progress by 3-4 miles per day Salt Water Intrusion Built to halt/ divert intruding salt water through the Mississippi River to protect habitats and drinking water
Sill Design
45 feet long, 45 feet tall
47 feet under water
Designed to create a reservoir to hold salt water Case Study:
Mississippi River Results
Successful in slowing salt water intrusion rate
Feasible mitigation technique on a short timeline (4-6 weeks total)
Will remain stable during drought-induced low river flow levels
Can be used as a model to apply to other estuarine zones in the same circumstance Case Study:
Mississippi River Farthest south Parish in Louisiana
2 sills installed in 1988 and 1999
Can be used to predict larger economic changes
Issues faced
Loss of production in fisheries, cattle ranches, and citrus groves are projected
Loss of $1 billion in shipping
Must import 5.5 million gallons of fresh water to meet human needs per year Sill Economics:
Plaquemines Parish, LA Sills are a viable way to slow down salt water intrusion rates
However, negative economic impact is high
Pros
Slows down intrusion rate
Under water infrastructure, no high impact on ecosystem
Cons
Expensive to build and maintain
May cause economic strain on the community around it
Not a true solution Conclusion Depiction of sill specifications References Dr. Jeff Masters' WunderBlog : America's Achilles' heel: the Mississippi River's Old River Control Structure | Weather Underground [Web log post]. (n.d.).

Elliott, D. (2013, January 29). Drought Causes Ripple Effect Along Mighty Mississippi River [Web log post].

Fagerburg, Timothy L., and Michael P. Alexander. "Underwater Sill Production for Mitigating Salt Wedge Migration on the Lower Mississippi River." Underwater Sill Production for Mitigating Salt Wedge Migration on the Lower Mississippi River (1994): 1-11. US Army Corp of Engineers. US Army Corp of Engineers. Web. 18 Apr. 2013.

Grunfield, David. "Greater New Orleans." The Times-Picayune. The Times-Picayune, 16 Aug. 2012. Web. 21 Apr. 2013.

Loftin, C. S., Aicher, S. B., & Kitchens, W. M. (2000). Effects of the Suwannee River Sill on the Hydrology of the Okefenokee Swamp: Application of Research Results in the Environmental Assessment Process. USDA Forest Service Proceedings RMRS-P, 3, 102-110.

McWhirter, Jan. Saltwater in Mississippi Taints Drinking Supply. 2013. The Wall Street Journal.

Morgan, Jan. Plaquemines Parish Profile, (2013). LSU AgCenter. Article
River closed as crews start work on sill | New Orleans CityBusiness [Web log post]. (n.d.).

Sanburn, Josh. The Not So Mighty Mississippi. (2013). Time.

US Army Corps of Engineers (2009). Old River Control. Case Study:
Mississippi River River flow and salt water intrusion Sill Economics:
Plaquemines Parish, LA River Sills River Sills Above River Sill
Full transcript