MODELING OF LAND BUILDING IN THE MISSISSIPPI DELTA: A TEMPLATE FOR RECONSTRUCTION

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MODELING OF LAND BUILDING IN THE MISSISSIPPI DELTA:A TEMPLATE FOR RECONSTRUCTION

Wonsuck Kim & Gary Parker, University of IllinoisAs part of a much larger team led by C. Paola (NCED) and R. Twilley (CLEAR)

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THE ORIGINS OF OUR LAND-BUILDING TECHNOLOGY:CAN HUMANS JUMP-START THE NATURAL DELTA-

BUILDING PROCESSES OF RIVERS?

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THE NATURAL PROCESS OF DELTA LOBE CONSTRUCTION AND SWITCHING

Lobe gif from M. Wolinsky

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DELTA MADE BY HUMANS:TAILINGS BASIN OF AN IRON MINE, LABRADOR, CANADA

Sediment disposal rate: ~ 24 Mt/yr

~ 2.4 km

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DELTA MADE BY HUMANS:TAILINGS BASIN OF AN IRON MINE, MINNESOTA

Sediment disposal rate: 21 Mt/yr

~ 3 km

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WE HAVE DEVELOPED AND VERIFIED NUMERICAL MODELS THAT DESCRIBE THE OVERALL EVOLUTION OF THESE

DELTAS DECADES INTO THE FUTURE

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HOW MUCH SEDIMENT IS CURRENTLY AVAILABLE FOR DELTA BUILDING IN THE MISSISSIPPI DELTA?

Input: ~ 208 Mt/yr

Wax Lake Delta:~ 34 Mt/yr

Atchafalaya River:~ 84 Mt/yr

Lower Mississippi River:~ 124 Mt/yr

Atchafalaya Delta:~ 50 Mt/yr

Suspended sediment loads

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Atchafalaya River

Mississippi River

Wax Lake Delta

The delta started to formed in 1973, when it received increased flow from the Atchafalaya River. Its growth has been monitored ever since.

TEST OF CONCEPT: NUMERICAL MODEL OF EVOLUTION OF THE WAX LAKE DELTA

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OUR MODEL CAN REPRODUCE THE WAX LAKE DELTA’S PAST

Before start of delta growth

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THE MODEL CAN REPRODUCE THE WAX LAKE DELTA’S PAST

Yellow: 38 Mt/yrWhite: 25 Mt/yr(suspended load)

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PREDICTIONS INTO THE FUTURE OF THE WAX LAKE DELTA

HIGH: Solid line, 38 Mt/yr; LOW dotted line: 25 Mt/yr (suspended load)

LOW

HIGHHIGH

LOW

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MIGRATION OF THE MODEL FROM WAX LAKE TO THE MISSISSIPPI RIVER BELOW NEW ORLEANS:

Two diversions: Barataria Bay and Breton Sound (CLEAR plan)

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POTENTIAL SEDIMENT FOR DELTA BUILDING:45% OF 124 Mt/yr, OR 56 Mt/yr (~ 3 iron mines)

Barataria Bay:28 Mt/yr delivered11 Mt/yr captured

Breton Sound:28 Mt/yr delivered11 Mt/yr captured

45% of floodwater and sediment diverted.

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SCENARIOS MODELED

100 year simulations from 2010Base case:

Subsidence: 5 mm/yr; sea level rise: 2 mm/yr

Variant parametersSubsidence: 1 mm/yr, 10 mm/yrSea level rise: 0 mm/yr, 4 mm/yr

Image from M. Wolinsky

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PRELIMINARY RESULTS FOR LAND-BUILDING: BASE CASE

Takes only about 0.1 years to build these initial deltas

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Base case:

918 km2 of new land

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VARIATION: SEA-LEVEL RISE RATE = 0 mm/yr, SUBSIDENCE = 5 mm/yrSolid line: variant caseDotted line: base case

1002 km2 of new land

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VARIATION: SEA-LEVEL RISE RATE = 4 mm/yr, SUBSIDENCE = 5 mm/yr

Solid line: variant caseDotted line: base case

845 km2 of new land

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VARIATION: SEA-LEVEL RISE = 0 mm/yr, SUBSIDENCE = 1 mm/yr

Solid line: variant caseDotted line: base case


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VARIATION: SEA LEVEL RISE = 2 mm/yr, SUBSIDENCE = 1 mm/yrSolid line: variant caseDotted line: base case


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VARIATION: SEA LEVEL RISE = 2 mm/yr, SUBSIDENCE = 10 mm/yrSolid line: variant caseDotted line: base case

753 km2 of new land

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VARIATION: SEA-LEVEL RISE = 4 mm/yr, SUBSIDENCE = 10 mm/yrSolid line: variant caseDotted line: base case

“Worst case”:

still 701 km2 of new land

And extra land-building due to organics is not yet included

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IN ORDER FOR THE DIVERSIONS TO BE SUCCESSFUL,

CONTROL STRUCTURES AND SHORT GUIDE CHANNELS, NOT OVERFLOW POINTS, ARE NEEDED

• We need to get as much sand as possible into the new deltas.• The present Caernarvon diversion, while helpful, delivers mostly mud.• We know how to build the control structures that divert sand as well as mud, because we built the Old River Control Structure to regulate flow into the Atchafalaya River.

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SLURRY PIPELINES CAN BE HELPFUL TO START LAND-BUILDING

IF SUSTAINED FOR MORE THAN A FEW YEARS, HOWEVER, THEY CAN BUILD DELTA SLOPES THAT ARE TOO STEEP.

http://www.lacpra.org/index.cfm?catid=0&elid=0&fmid=0&md=pagebuilder&nid=31&pid=20&pnid=24&tmp=home

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NEXT STEP: BUILD IN THE FINE STRUCTURE

Our field effort on the Wax Lake Delta is our main template.

(m)

-0.3 - 00.30.60.91.21.5

• The land-building model predicts overall topography.• We are using field measurements to build in the statistical structure of

bars/channels/edge effects/ etc. necessary for ecosystem modeling.

Many species of fish like this edge zone near bars.

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BUILD IN THE ECOLOGICAL COMPONENTS OF THE NEW DELTA

Most of these components are already in place at Louisiana State University and within the CLEAR group in Louisiana.

NEXT STEP:

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NEXT STEPS:CONSIDERATIONS OF SUCH FACTORS AS

• Effect of diversions on Mississippi River upstream• Coastal sediment supply• Storm surge• Navigation• Socioeconomic implications: e.g. oyster farms, shrimp• POLITICAL WILL

AMBITIOUS PROJECTS ARE POSSIBLE!Parker’s great-grandfather and great uncle were construction workers on this

first bridge to span the Mississippi River in New Orleans

Levee strengthening will be

needed in the short term

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Most of the Mississippi Delta, some 10,000 square miles, lies less than three feet above sea level. Beset by land subsidence and rising sea levels, much of this vast area will inexorably sink beneath the waters by the end of this century.

BRUCE BABBITT

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BRUCE BABBITT

Before major human intervention, the Mississippi Delta historically maintained itself with river slopes on the order of 3 ft of drop per 30 miles without sinking beneath the waters!

How? The surface is NOT a static “board” that will sink because of its low slope – it is a DYNAMIC, self-maintaining surface that keeps itself from drowning by adding sediment to balance subsidence.

Think about your bank account.

If you withdraw $1,000 a month every month, you will go broke before long.

How can you fix the problem?

OUR REPLY

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BRUCE BABBITT

START DEPOSITING $1000 A MONTH!

OUR REPLY

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WE THINK THAT THE SCIENCE AND TECHNOLOGY EXISTS TODAY TO REBUILD A NEW, LIVING MISSISSIPPI DELTA

Wax Lake gif from M. Wolinsky

Documents

MODELING OF LAND BUILDING IN THE MISSISSIPPI DELTA: A TEMPLATE FOR RECONSTRUCTION