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/
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