Changing Nature’s Course Tracy Morris David Trombley

A War of Two Rivers 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

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.

How It All Began 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

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

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

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”

Flood Control 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

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

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

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

Old River Control Structure Low 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

Old River Control Structure Overbank Structure Contains 73 bays –Each 44 ft wide –Total length 3,356 ft

Old River Control Structure Auxiliary Control Structure Completed in 1986 Total of 6 gates –62 ft wide –Total length 442 ft

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

Other Control Structures Bonnet Carre Spillway –Built 1937 –Diverted water to Lake Pontchartrain

References 1927 Flood Pictures: F8CB394C2B9F.shtmlhttp:// F8CB394C2B9F.shtml Pictures of control structure: Spring2002/Cathrine_Duex/OldRiverControl.html Spring2002/Cathrine_Duex/OldRiverControl.html crawfish.ssihttp:// crawfish.ssi

Questions?