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Mississippi on the move: in a battle of humans versus nature, engineers strategize to pull the plug on a flood.

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Last May in Missouri, loud explosions thundered in the night. The blasts put a hole right through Birds Point Levee--an earthen embankment that had held back a swollen Mississippi River. Water rushed through the breach, flooding farmland. But the explosions were no accident. They were part of a plan to prevent worse devastation.

With 41 percent of the waterways in the continental U.S. draining into the Mississippi, the mighty river has the third-largest watershed in the world. Last spring, huge amounts of rainfall and snowmelt force-fed the river more than it could handle. As the Mississippi overflowed and flooded towns along its banks, the U.S. Army Corps of Engineers pulled out all the stops to lessen the damage. Did their plan work?

FLOOD FIGHT

Drama is nothing new to the Mississippi, which is a tricky river that has altered its course throughout history (see A River Changes Course, left). A shape-shifting river creates big problems for local residents and for shipping. Therefore the Corps launched the Mississippi River and Tributaries Project in 1928. The plan included building levees to maintain the river's course as it winds along 3,700 kilometers (2,300 miles) from Minnesota to the Gulf of Mexico.

The levees were no match for last spring's deluge. So engineers used their next line of defense--reservoirs. Clint Wilson, a civil engineer at Louisiana State University, compares these reservoirs or human-made lakes to bathtubs that workers can drain or fill by opening or closing a dam. "When all the rainwater and snowmelt come down, you can store a lot of it behind the dam," he explains. The strategy gives the river more time to send its waters downstream.

But the Mississippi continued to rise as its tributaries poured in water from all directions. Willson says, "Think about trying to leave a ballgame when you've got only one road that's going out, and you've got 20 lanes from a parking lot that are feeding into it." Traffic backs up--and so did the river waters, threatening to overflow levees.

LAST RESORT

To save more-densely-populated areas, engineers made a tough call: Open Birds Point Levee and allow water to pour into the low-lying New Madrid Floodway (see map, below). "It's about 130,000 acres that become available almost instantaneously to the river as a place to store water," says Larry Banks, a retired Corps hydraulic engineer who returned to help handle the crisis. Floodways give the river room to expand, so it doesn't back up. This last-ditch measure-which hadn't been implemented since 1937--meant sacrificing about a hundred homes and vast amounts of precious farmland in the floodway.

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After dark on May 2, with the muddy waters rising, workers detonated the charges. They opened two more breaches in the following days. The river lowered, taking pressure off the region's levees. But as the Mississippi continued along its course, picking up more water, danger flowed south.

RISING RIVER

Far downstream, in New Orleans, Louisiana, Corps engineers monitored the rising torrent. On May 9, they began activating a second floodway--the Bonnet Carre Spillway. This time, they didn't need explosives. Cranes lifted wooden timbers that blocked openings in a long, concrete structure along the river. Water gushed through the openings, flowed nearly 9.6 km (6 miles) across the floodway--which contains a campground but no permanent homes--and then spilled into Lake Pontchartrain.

Five days later, the river was still rising. To protect the densely populated cities of Baton Rouge and New Orleans, the Corps did something they had done only once before: They activated the Morganza Floodway upstream. After warning people in the danger zone to evacuate, they gradually opened gates in the concrete structure. The Corps was also concerned for the wildlife living in the region. "We operated Morganza rather slowly at first to give a warning sign for the wildlife there to get out," says Banks.

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With 17 of Morganza's 125 gates open, the situation stabilized. The swollen river--which had prompted the Corps to take the unprecedented action of opening three floodways at the same time-passed its floodwaters along to the Gulf of Mexico. By late June, water levels were still well above normal, but workers had closed the Bonnet Carre Spillway and all but one of the Morganza gates, and work was under way to close the breaches at the Birds Point Levee. Many of the evacuees had returned to deal with the extensive damage. The next step for the Corps: Inspect the flood-control system which worked as planned during the emergency--and make needed repairs to prepare for next time, because if the past is any indicator, the Mississippi River will continue its wily ways.

A RIVER CHANGES COURSE

The mighty Mississippi River has taken many routes over the years. In 1944 a cartographer named Harold Fisk drew a map of the Mississippi as it flowed then (beige ribbon). Working backward from geological maps, he also drew the river as it had been in earlier decades (colored ribbons). The river continues to carve out new pathways, despite engineers' best efforts to tame it.

[WHAT DO YOU THINK?]

Was it right for engineers to flood some homes and farms in order to spare more-densely-populated regions? Support your opinion with facts from the text.

RELEASING THE FLOODWATERS

This spring, engineers blasted a levee and opened flood gates to try to lower the Mississippi's rising waters. This map shows each opening.

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STANDARDS

NATIONAL SCIENCE EDUCATION STANDARDS:

Grades 5-8: Structure of the Earth system

Grades 9-12: Natural and human-induced hazards

COMMON CORE STATE STANDARD:

READING INFORMATIONAL TEXT:

8. Trace arguments and evidence

OBJECTIVE

Understand reasons why the Mississippi River flooded last spring and the decision to intentionally flood certain areas.

BEFORE READING

* What is a flood? (when waters, such as rivers, rise to unusually high levels)

* How do floodwaters affect the land they cover? (They destroy crops, buildings, and homes, and can kill people.)

* What can humans do to control floods? (They can build dams, levees, put up temporary blocks, etc.)

LESSON

1. Go to www.scholastic.com/scienceworld. Open up the digital edition to pages 14-15 and have students do the same in their magazines. Point out that the article runs vertically in the magazine. (The digital version of the article, however, has been reformatted to fit the screen horizontally.).

[DIGITAL STICKY NOTES] 2. Ask your students why they think the editors chose to display the print article this way. Record their answers in a digital sticky note. (Since the Mississippi is the longest river in the U.S. and runs north to south, the best way to display the map was running down the left-hand side of the article.)

[VIDEO PLAYER] 3. Play the video about the Mississippi River to introduce students to the river and the recent flood.

4. Call on a volunteer to read the headline, the text just below it and the introductory paragraph. Ask for student reactions: Did they hear about the flooding? Did they have friends or family affected by the floods?

5. Continue to have volunteers read the article. At the end of each section, have students talk as a class about their reactions to the unfolding drama of the Mississippi River Basin flooding.

DISCUSSION

Read the text in the box labeled "What Do You Think?" on page 16: "Was it right for engineers to purposely flood some people's homes in order to spare more-densely-populated regions?" Hold a class debate, either assigning sides or allowing students to choose. You may want to have each student work with a partner or small group to help them develop solid, evidence-based arguments.

ASSESSMENT

Use the "Cause and Effect" work sheet from the online skills sheets database at www.scholastic .com/scienceworld to determine the causes and effects of the main events in the Mississippi River flooding this spring.

DON'T TEACH EARTH SCIENCE?

Go to www.scholastic.com/scienceworld to download these assessment skills sheets instead:

BIOLOGY: HARVEST TIME

The Mississippi River Basin in southeast Missouri, where the Birds Point Levee is located, produces several important grain crops. Use this graphing activity to compare the number of acres harvested in 2010 and learn more about the crops that might be affected by the flooding.

PHYSICS: RISING WATERS

Flowing water is typically measured in cubic feet per second (cfs), but this may be a difficult unit for students to picture. Try this conversion activity to help your students understand this unit of measurement by comparing it with units more familiar to them.

RESOURCES

* VIDEO EXTRA: Watch a video about the Mississippi River at: www.scholastic.com/scienceworld.

* Find more information about floods and flood-relief efforts in the United States at: www.fema.gov/hazard/flood/info.shtm.

* Learn about the history of the Mississippi River and Tributaries Project at: www.mvn.usace.army.mil/pao/bro/misstrib.htm.
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Title Annotation:earth: rivers; Mississippi River
Author:Adams, Jacqueline
Publication:Science World
Geographic Code:1USA
Date:Oct 17, 2011
Words:1473
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