Changing Nature’s Course

1. Changing Nature’s Course Tracy Morris David Trombley

2. Atchafalaya Controls Louisiana’s crawfish crop Basin encompasses over 370,000 acres of fresh marsh, bottomland hardwoods, cypress swamps, and open water (the largest wetland in the US) Mississippi Drains 41% of the contiguous US Basin covers more than 1,245,000 square miles Lower alluvial valley is a flat plain of 35,000 square miles A War of Two Rivers

3. Map of Southern Louisiana Today The Old River connects the Mississippi to the Atchafalaya. The Atchafalaya runs a much shorter course to the Gulf of Mexico. Commerce has depended on the Mississippi for 200 years.

4. How It All Began • 1831- Old River created by steamboat captain to shorten his upriver trip • Old River flow slowed as the upper portion filled with silt • 1839 – State of Louisiana began to clear 30 mile logjam on Atchafalaya River • Flow in Atchafalaya began increasing

5. If It Did Switch Course? • New Orleans ranks number 1 in the United States in tonnage of goods shipped through its port • The Mississippi River is associated with 40% of the tidal wetlands in the contiguous United States • Riverside development along Atchafalaya would be inundated

6. Change Isn’t Always Good • Businessmen quickly realized that they needed the Mississippi to remain a navigable river • In 1927, a 100-year flood gave us a second reason to control the flow

7. The Flood of 1927 • Inundated 16.5 million acres in 7 States • Destroyed: $102 million of crops 160,000 homes 40,000 buildings • Killed 500 people • Prompted Congress to pass “Flood Control Act of 1928”

9. Corps accepted over 300 proposals Winning proposal had three facets: Incorporate floodways to divert peak flow Create backwater areas Design all works on basis of a great hypothetical flood Flood Control

10. Slowly but Surely • 1953- Mississippi River Commission recommended an Old River Control Structure • 1954- Corps engineers designed a lock, a dam over the Lower Old River and two control structures: Overbank and Low Sill • 1955- Construction began

11. Old River Control Structure • Completed in 1962 • Kept Acadiana from flooding • Keep enough water in Mississippi so big ships can navigate to New Orleans • Composed of dams, weirs, and levees • Designed to allow 30% of the Mississippi to flow down Atchafalaya under normal times

12. Old River Control Structure • Without control structure, the straighter shorter Atchafalaya would capture the mainstream of the Mississippi

14. Old River Control StructureLow Sill Structure • Made of eleven gates • 44 ft wide • Total length 566 ft • Maximum water height allowed in forebay • 69.8 ft above sea level • Designed to withstand a 37 foot difference in water levels between Mississippi an Atchafalaya • Can only maintain 22 ft

15. Old River Control StructureOverbank Structure • Contains 73 bays • Each 44 ft wide • Total length 3,356 ft

16. Old River Control StructureAuxiliary Control Structure • Completed in 1986 • Total of 6 gates • 62 ft wide • Total length 442 ft

19. Old River Control StructureNavigation Lock • Allows travel between Mississippi, Red and Atchafalaya rivers • 75 ft wide • 1,185 ft long • Floor 11 ft below sea level

20. Other Control Structures • Bonnet Carre Spillway • Built 1937 • Diverted water to Lake Pontchartrain

21. References • 1927 Flood Pictures: http://www.riddlelawoffice.org/1927Flood.shtml • http://www.mvd.usace.army.mil/offices/pa/brochures/mrtbrochure.pdf • http://www.biology.lsu.edu/webfac/cramcharan/Louisiana.html • http://www.theadvertiser.com/news/html/BF4039D3-B1D9-497C-AB63-F8CB394C2B9F.shtml • http://www.tulane.edu/~bfleury/envirobio/enviroweb/FloodControl.htm • Pictures of control structure: http://www.msstate.edu/dept/geosciences/CT/TIG/WEBSITES/LOCAL/Spring2002/Cathrine_Duex/OldRiverControl.html • http://www.dnr.state.la.us/sec/execdiv/pubinfo/newsr/archive/ crawfish.ssi • http://www.lacoast.gov/cwppra/projects/atchafalaya/

22. Questions? Questions?