Five Feet High and Rising

Historical and

Ecological

Perspectives of the

Bonnet Carré

Spillway Adam D. Boyette

School of Ocean Science and Engineering The University of Southern Mississippi

August 27, 2019

Disclaimer

This presentation was prepared by the presenter, Adam Boyette, in his personal capacity. The opinions

and information expressed in this presentation are the author’s own and do not reflect the view of

The University of Southern Mississippi, the Mississippi Department of Marine Resources, the Mississippi

Department of Environmental Quality, the U.S. Army Corps of Engineers, or any other state or federal

government entity.

Presentation Overview

• Current news (prologue)

• Ecology

• A brief history

• Ecological impacts

• Concluding remarks

• Questions?

“The current oyster mortality rate is estimated at 70%...crab landings are currently estimated at a 35%

loss…[and] the impact on marine finfish is currently being assessed and that the impact of freshwater on ‘larval

growth and juvenile recruitment’ could impact the fishery for many years to come.” -Gov. Phil Bryant

Though the Bonnet Carré Spillway was closed on July 27, Mississippi coastal communities are still seeing effects resulting from vast amounts of freshwater that impacted the region.

On May 31, 2019 Gov. Phil Bryant issued a disaster declaration for Mississippi in response to adverse ecological impacts resulting from freshwater surging into Mississippi coastal waters from the Bonnet Carré Spillway opening.

Gulf of Mexico

Gulf of Mexico

Mississippi Bight

The northern Gulf of Mexico is one of the most biologically productive regions in North America, making it one of the

most productive water bodies in the world.

Marine Ecology

• The mighty phytoplankton!

• River-borne nutrients are essential for stimulating phytoplankton, the base of the marine food web.

• Important for sequestering carbon (PHOTOSYNTHESIS) Accounts for ~ 40% of Earth’s total photosynthesis!!!

Ecological Impacts • Overabundance of nutrients also can stimulate too much

phytoplankton growth, causing severe ecological problems (eutrophication)

– Harmful algal blooms • Fish kills

• Toxic waters

– Low oxygen “dead zones”

Karenia brevis

Hypoxia

“Dead Zone”

• Largest hypoxic zone in the United States and 2nd largest in the world

• Hypoxic zones are areas in

the ocean with such low oxygen that the region is devoid of life

Courtesy of NOAA

Less dense fresh water “lens”

pycnocline

More dense saltwater

Courtesy of NOAA

Justic et al. 2019

0% reduction in nitrogen

25% reduction in nitrogen

50% reduction in nitrogen

Hypoxia in the Mississippi Bight

Dzwonkowski et al. 2017

Gulf of Mexico

Mississippi Bight

“The Big Muddy”

• Largest river in North America and 3rd largest drainage basin in the world

• Drains 41% of the 48

contiguous U.S. comprising 15,000 mile inland river system

• Basin covers 1.25 million

square miles

NASA Visible Earth: Lake Pontchartrain and the Bonnet Carré Spillway, Louisiana (April 29, 2008)

spillway control structure

spillway

New Orleans

Lake Pontchartrain

15 Photo courtesy USACE

A Brief History

Bonnet Carré Spillway • Constructed at the site of a naturally-occurring crevasse • 7,000 foot long flood control structure ~30 miles above New

Orleans. • Floodway extends 5.7 miles from the Mississippi River to Lake

Pontchartrain. • Design capacity of 250,000 cfs to reduce flow in the Mississippi River

downstream of the floodway in order to protect New Orleans

US Army Corps of Engineers New Orleans District operates the Bonnet Carré Spillway

Spillway opens when local MS river discharge gauges read above 1.25 million cubic feet per second (cfs)

13 Photo courtesy USACE

Early European Settlements • Levee construction began with the first settlers

along the Mississippi River

– Early 18th century French settlements constructed levees along the banks of New Orleans modeling those in France

– 5,400 feet long x 18 feet wide x 4 feet high

Early Levee Construction • Not reliable and floods frequently devastated these

“primitive” levee systems

– Dread and anxiety every year throughout the lower Mississippi River valley.

– People who lived along the river were responsible for constructing & maintaining the levees themselves

• Haul methods would

yield ~10-12 cubic yards per day with a haul limit of 75 feet

Early Legislation • 1820 the first Federal involvement

along the Mississippi River focused on navigation, not flood control. – Consisted of creating cuts and

shortening the main channel.

• 1850 Congress appropriated $50k to conduct two hydrographic surveys of the Mississippi River: The Humphreys-Abbot report – Considered (3) methods of flood

protection: 1. Cutting off river bends 2. Diversion of tributaries and creating

artificial reservoirs and outlets 3. Confining the river to its channel via

an extensive levee system

Early Legislation • Cutting off river bends and creating

tributary diversions was deemed too costly.

• Recommended confining the river channel via levees

• Between 1850-1927 levees along the lower Mississippi had to be continuously raised because the river bed had elevated due to increased confinement caused by levee construction;

• The Civil War left the levees in disrepair, which was only exacerbated by severe floods in the late 1860’s and 1870’s.

• 1879-Mississippi River Commssion

Mississippi River Commission • Flood control viewed as

integral to river navigation

• Greatest detriment to levees was river instability and bank caving.

• Construction of a levee system that would contain frequent floods resulting in a “self-cleansing” of the river.

• Flooding continued and many of the levees were unable to contain the river

U.S. Army Corps of Engineers

• 1917 – the U.S. Government ordered the USACE to address this flooding at the behest of the community officials (Federal Flood Control Act, 1917)

• “Levees Only” philosophy to control the great floods of the Mississippi River. – Increase amount of water in river to scour out and deepen

river bed

• 10 years to complete the “Levees Only Project” – 40 feet tall x 100 feet wide

– 1000 miles on both sides of the river (Cairo, Illinois to the Gulf of Mexico).

The river was in effect “shackled” Courtesy USACE

“…ten thousand River Commissions cannot tame that lawless

stream…cannot say to it, ‘Go here,’ or ‘Go there,’ and make it

obey.”

-Mark Twain

• August 1926, rains began & lasted for 8 months, bringing the river to record gauges.

• Record rainfall in spring 1927 led to catastrophic failure of levees

– April 21st was the first crevasse

– estimated 120 breaks before the flooding ended

Great Flood of 1927 “The roar of the crevasse drowned all sound. It carried up

and down the river for miles, carried inland for miles. It

roared like some great wild beast proclaiming its

dominance…quickly the crevasse widened, until a wall of

water three quarters of a mile across and more than a

hundred feet high raged into the Delta.”

- J. M. Barry from Rising Tide

A tale of two stories: man vs. nature and man vs. man

• A week after the first break the full force of the flood was headed to New Orleans

• Never, under any circumstance, allow the river to threaten the city

– Levee dynamited at Caernarvon to save New Orleans

– Over 4,000 people were homeless in the rural parish

• More than 500 dead

• 16.6 million acres flooded

• 162,000 homes lost

• 325,000 refugees

• Over $400 million in damages (= $5.7 billion today)

• Threatened New Orleans, the financial center of the South.

• Blast breach at Caenarveron in St. Bernard Parish 13 miles downriver from New Orleans

• Catalyst for 1928 Flood Control Act – Promotion of improved levees and introduction of

spillways to control flooding along the Mississippi River and to protect New Orleans (Jadwin Plan)

Great Flood of 1927

1928 Federal Flood Control Act

• Included the Mississippi River and its tributaries and adopted new levee standards

• Concept of floodways implemented: passage of excess flows through diverted zones

• Floodways along the MSR: – Birds Point-New Madrid* – Morganza Floodway – West Atchafalaya Floodway – Bonnet Carré Floodway

(Spillway)

Courtesy USACE

Bonnet Carré Spillway • Studies determined the best

location for spillway was at Bonnet Carré Crevasse, the site of naturally-occurring crevasses

• 1849-1882 had four major crevasses, one that lasted more than 6 months

• USACE concerned with two problems: 1. Possibility that the river might

cut a channel through the spillway and divert its course;

2. Whether the soft sediment could support the massive concrete structure

Courtesy USACE

Bonnet Carré Spillway • 1929 – 1931 construction

• 350 bays each with 20 creosote timbers (needles) removed by rail-mounted gantry cranes

Courtesy USACE

Year Open and Close Dates

(duration) % Bays

Opened Estimated

Total

Discharge

(km3)

Lake

Pontchartrain

Volume

Percentage

Data Source

1937 Jan 28 - Mar 16 (48 days) 81% 15.2 238% War Department (1937)

1945 Mar 23 - May 18 (57 days) 100% 30.1 470% Dept. of Army (1945)

1950 Feb 10 - Mar 19 (38 days) 100% 13.4 209% Corps of Engineers (1950)

1973 Apr 8 - Jun 21 (75 days) 100% 23.5 367% USACE (1974)

1975 Apr 14 - Apr 26 (13 days) 64% 2.11 33% USACE (1975)

1979 Apr 17 - May 31 (45 days) 100% 13.9 217% USACE (1980)

1983 May 20 - Jun 23 (35 days) 100% 15.2 238% USACE (1984)

1997 Mar 17 - Apr 17 (32 days) 85% 11.7 183% Perret et al. (1997)

2008 Apr 11 - May 8 (28 days) 46% 7.5 117% USACE (2019)

2011 May 9 - Jun 20 (43 days) 94% 21.9 342% USACE (2019)

2016 Jan 10 - Feb 1 (23 days) 60% 6.9 107% USACE (2019)

2018 Mar 8 - Mar 30 (23 days) 52% 5.8 91% USACE (2019)

2019 Feb 27 - Apr 11 (44 days) 59% 15.1 236% USACE (2019)

2019 May 10 - Jul 27 (79 days) 48% 23.0 360% USACE (2019)

Courtesy Parra et al. (in review)

Gulf of Mexico

Mississippi Bight

2018 harmful algal bloom in Lake Pontchartrain following the opening of the Bonnet Carré Spillway

Ecological Impacts

A History of Ecological Impacts • 1937 – “…diversion of flood waters

introduced organic material into Lake Pontchartrain and beyond the Mississippi Sound.“

• 1950 – “In years of heavy spillway

discharge, about 100% of the oysters in Mississippi Sound west of Bay St. Louis are killed.”

• 1997 – the combined factors of

reduced salinity, cyanobacteria blooms, and hypoxia appear to have had a deleterious impact on benthic macrofauna.

• 2008 – effects of discharging fresh

nutrient-rich river water into Lake Pontchartrain had cascading impacts to water quality and phytoplankton communities, with cyanobacterial blooms negatively impacting aquatic communities.

Characterize a large plume of Mississippi River freshwater entering Mississippi coastal waters via Lake Pontchartrain due to first-ever

wintertime opening of the Bonnet Carré Spillway

• (3)-day cruise in the Mississippi Bight to describe physical, chemical, and biological properties of river dominated waters

2016 wintertime Bonnet Carré Spillway opening

12-Jan 2016 Day 2

Spillway began opening on Jan. 10 (Day 0)

13-Jan 2016 Day 3

16-Jan 2016 Day 7

17-Jan 2016 Day 8

18-Jan 2016 Day 9

19-Jan 2016 Day 10

23-Jan 2016 Day 14

24-Jan 2016 Day 15

26-Jan 2016 Day 17

Spillway began closure on Jan. 25 (Day 16)

29-Jan 2016 Day 20

04-Feb 2016 Day 26

Spillway closed on Jan. 31 (Day 22) + 4 days

05-Feb 2016 Day 27

+ 5 days

07-Feb 2016 Day 29

+ 7 days

08-Feb 2016 Day 30

+ 8 days

09-Feb Day 31

+ 9 days

10-Feb

BCS01 Cruise: Day 1

Day 32

+ 10 days

11-Feb

BCS01 Cruise: Day 1

BCS01 Cruise: Day 2

Day 33

+ 11 days

12-Feb

BCS01 Cruise: Day 1

BCS01 Cruise: Day 2

BCS01 Cruise: Day 3

Day 34

+ 12 days

13-Feb Day 35

+ 13 days

• Bonnet Carré Spillway waters remained within the estuarine lakes and sounds due to the short opening duration and local winds

• Bio-optical and chemical data showed differences between local rivers and Mississippi River influenced waters

• Local rivers were the primary source of freshwater within the Mississippi Bight

• Regional circulation primarily driven by winds during spillway opening

• The largest February monthly chl-a anomalies in the Bight in 2016 relative to the previous 15 years

• Phytoplankton and zooplankton communities were mainly diatoms and copepods

2016 wintertime Bonnet Carré Spillway opening

Parra et al. (submitted)

• Bonnet Carré Spillway waters remained within the estuarine lakes and sounds due to the short opening duration and local winds

• Bio-optical and chemical data showed differences between local rivers and Mississippi River influenced waters

• Local rivers were the primary source of freshwater within the Mississippi Bight • Regional circulation primarily driven by winds during spillway opening • The largest February monthly chlorophyll-a anomalies in the Bight in 2016 relative to

the previous 15 years • Phytoplankton and zooplankton communities were dominated by diatoms and

copepods, respectively

2016 wintertime Bonnet Carré Spillway opening

Parra et al. (submitted)

2016 study provided us the opportunity to develop better circulation models, which may be used to forecast river diversion plume waters for environmental managers

2016 wintertime Bonnet Carré Spillway opening

Parra et al (submitted)

2019: A Year of 1sts

• First time the Bonnet Carré Spillway was opened twice in the same year;

• First time the Bonnet Carré Spillway was opened in back-to-back years.

• Combined openings equivalent to largest estimated discharge into Lake Pontchartrain

• Opened an unprecedented 4 times in 5 years.

1ST Opening Feb. 27-Apr.11

44 days

2nd Opening May 10-Jul. 27

79 days

Hurricane Barry

USGS site

Figure courtesy of DMR Commission of Marine Resources

August 20, 2019

>90% loss of oysters

~40% of the 5 year average

~25% of the 5 year average

• Mid-June algal bloom reported to DMR in western MS Sound. – Dolichospermum spp. & Microcystis spp. freshwater

cyanobacteria species that produces toxins;

• June 22, MDEQ closed beaches in Hancock County, but by

early July, entire Mississippi shoreline closed

• August 12: HAB and additional water contact warnings issued by the MSDEQ, govenor may request an Economic Injury Declaration from the Small Business Administration

Photo: Mark Wright/Special to Clarion Ledger Photo: Mark Wright/Special to Clarion Ledger

Photo: MSDMR

HARMFUL ALGAE BLOOMS (HABs)

Dolphin and sea turtles • According to Institute for Marine Mammal Studies (IMMS) in

Gulfport, 130 dolphins and 154 sea turtles have been found dead in Mississippi coastal waters as result of the freshwater impact.

• Most have lesions, which are caused by low salinity conditions.

• Although exact cause of deaths are unclear, it is related to the “freshwater environment.”

(Photo: Institute for Marine Mammal Studies/Special to Clarion Ledger)

August summary of ecological impact the 2019 Bonnet Carré Spillway Opening

• Oyster mortality extensive (>90 % mortality)

• Significant decrease in shrimp (▼50% ) & crab (▼30% ) landings compared to the 5 year average

• 130 dolphins and 154 sea turtles found dead from prolonged exposure to low salinity water

• Widespread harmful algae bloom prompting closure of ALL beaches

• Significant impact to tourism

2019 Bonnet Carré Monitoring Update • Full closure achieved on July 27, 2019 • Salinity ‘normal’ in central & western Mississippi Sound • Water contact warnings remain in effect for coastal

waters immediately adjacent to Mississippi Gulf Coast beaches due to presence of cyanobacteria capable of producing toxins. MDEQ and MDMR continue to sample waters from those areas daily.

• MDMR continues to test water and fish samples to ensure seafood safety. – Avoid catching seafood where algae is present – Offshore fishing in Mississippi waters remains unaffected by

the algal bloom and those catches are safe for consumption.

Closing Remarks

• The Bonnet Carré Spillway remains one of the primary flood control systems on the Mississippi River.

• Despite ecological impacts to Mississippi coastal waters, the spillway will continue to be used.

• Research from 2016 suggests that the time of year in which openings occur may reduce the impact of Mississippi River freshwater on coastal ecosystems. – Open the spillway earlier?

• Changing weather patterns due to climate change will impact precipitation throughout the Mississippi River valley.

• Underscores the need for long-term ecosystem monitoring to address coastal eutrophication

Acknowledgements

• Joyce Shaw (Gulf Coast Research Lab)

• Kemal Cambazoglu (Division of Marine Science)

References 1. Barnett, J. F. 2017. Beyond Control: the Mississippi River’s new channel to the Gulf of

Mexico. University of Mississippi Press.

2. Barry, J. M. 1997. Rising Tide: the Great Mississippi Flood of 1927 and how it changed America. Touchtone.

3. Brammer, A. J. et al. 1997. Effects of the 1997 Bonnet Carré Spillway opening on infaunal macroinvertebrates in Lake Pontchartrain, Louisiana. Journal of Coastal Research, 23(5).

4. Dzwonkowski, B. 2017. Estuarine influence on biogeochemical properties of the Alabama shelf during the fall season. Continental Shelf Research 140:96–109.

5. Gunter, G. 1953. The relationship of the Bonnet Carré Spillway to oyster beds in Mississippi Sound and the “Louisiana Marsh,” a report on the 1950 opening. Publications of the Institute of Marine Science 3(1).

6. Howard, J.A. & W. T. Penfound. 1942. Vegetational studies in areas of sedimentation in the Bonnet Carré floodway. Bulletin of the Torrey Botanical Club, 69(4).

7. Mize, S. & D. K. Demcheck. 2009. Water quality and phytoplankton communities in Lake Pontchartrain during and after the Bonnet Carré Spillway opening, April to October 2008, in Louisiana, USA. Geo-Mar Letters.

8. Parra, S. et al. (manuscript submitted to Continental Shelf Research)

9. US Army Corps of Engineers https://www.mvn.usace.army.mil/Missions/Mississippi-River-Flood-Control/Bonnet-Carre-Spillway-Overview/Spillway-Operation-Information/

Questions?

Thank You!

Contact information: adam.boyette@usm.edu