Historic spillway opening sparks debate over potential environmental impacts
By Chaffin Mitchell, AccuWeather staff writer
May 15, 2019, 3:32:50 PM EDT
The historic second opening in a year of the Bonnet Carré Spillway last week has sparked concern about the effects it will have on Lake Pontchartrain, after marine wildlife washed ashore following the first opening.
The first opening of the spillway this year occurred on Feb. 27 and led to controversy regarding the impact on wildlife, because the spillway is known to have effects on the water quality in Lake Pontchartrain. Officials in Mississippi and Louisiana have been debating whether that contributed to the deaths of 45 dolphins and 25 turtles that washed ashore earlier this year, The Advocate reports.
Now the debate is getting more attention because the Army Corps of Engineers reopened the Bonnet Carré Spillway again on May 10. This is the 14th operation of the structure since 1937.
When the spillway is opened, materials are deposited in Lake Pontchartrain and Lake Borgne. Since the lake is an estuary with a mix of fresh and salt water, releasing fresh water into these brackish and saline lakes has an immediate, short-term, adverse environmental effect.
The Army Corps of Engineers also try to limit spillway openings to minimize the impact of invasive freshwater species entering the Lake Pontchartrain basin.
However, according to the Army Corps of Engineers, the long-range effect is favorable because it simulates the natural flooding cycle of the river and provides a replenishment of valuable nutrients to the ecosystem. Spillway openings are strongly associated with increased oyster, crab and other fisheries production in both lakes for several years after the flood events.
“Trillions of gallons have come down from the Bonne Carré Spillway. That has changed the habitat, the food source and all sorts of changes for these animals,” Moby Solangi with the Institute of Marine Mammal Studies in Mississippi told WAFB.
Too much fresh water can stunt shrimp growth, which could lead to a later or less impressive season, a Louisiana Wildlife and Fisheries assistant secretary, Patrick Banks, told The Advocate. The rapid changes in temperature and salinity can push already stressed animals over the edge, such as dolphins and their calves. Some people are also concerned about the impact of fresh river water on oyster fisheries.
With each opening, the river deposits an average of 9 million cubic yards of sediment, mostly silts and sand, within the floodway. According to the Corps, these deposits are removed by private contractors and local government agencies for use as fill material in residential and industrial developments. This sediment is a valuable local resource since most of the surrounding region is near or below sea level.
While water levels on the Mississippi remain high, the flood control system in place is capable of handling more water.
"We have a system in place and that system is able to pass high water events far greater than what we have today," Ricky Boyett, an Army Corps of Engineers spokesman, told the AccuWeather Network. "We've never actually maximized what the system can do. So when we talk about the flood, that is a term for the high water; however, fortunately we're able to keep the water between the levees and prevent it from getting into homes and property."
The Lake Pontchartrain Basin Foundation (LPBF) and environmental groups monitor the lake during and after an opening to determine the effects the opening has on salinity and nutrient levels.
"The Lake's water quality is directly related to rainfall runoff. If it has rained in your area in the past three days, the runoff could pollute the lake," the LPBF website states.
Rising Mississippi River prompts historic opening of Bonnet Carré Spillway near New Orleans
Wettest 12-month period on record leaves US nearly drought-free amid rampant flooding
Flooding forces Bonnet Carré Spillway to open
Any negative effects and imbalances could lead to toxic algae blooms that are harmful to humans and animal health.
"It's really important to get metrics and try to understand with each opening [of the spillway] what the level of environmental impact is," Dr. Brady Skaggs, the foundation's water quality program director, told the AccuWeather Network.
In the past, the lake has experienced blooms including blue-green algae. Large algae blooms also can cause low-oxygen dead zones at some locations on the lake bottom. When the algae dies, it sinks to the bottom and decomposes, which uses up oxygen.
The LPBF has been planning on gathering information about the effects of opening the spillway two years in a row.
Comments that don't add to the conversation may be automatically or manually removed by Facebook or AccuWeather. Profanity, personal attacks, and spam will not be tolerated.
More Weather News
Weather News - May 23, 2019, 3:12:06 AM EDT
Three fatalities have been reported near Golden City, Missouri, as a severe thunderstorm outbreak hit Oklahoma to Illinois on Wednesday. A tornado also struck the capital city of Jefferson City, Missouri, producing extensive damage.
Weather News - May 22, 2019, 10:53:58 PM EDT
This Memorial Day weekend is set to have the second-highest travel volume on record since AAA began tracking holiday travel volumes in 2000; INRIX predicts drive times could be more than three times longer than normal.
Weather News - May 22, 2019, 3:29:09 PM EDT
Isolated tornadoes are among the dangers as a surge of heat and humidity helps to fuel severe thunderstorms in the northeastern United States on Thursday.
Weather News - May 22, 2019, 7:14:01 PM EDT
After a severe weather outbreak hammered areas from Texas to Kansas and Missouri early this week, more severe weather will threaten these same areas in the days leading up to the Memorial Day holiday weekend.
Weather News - May 22, 2019, 3:46:01 PM EDT
Temperatures approaching the century mark amid the hottest weather yet this year will challenge records in many places that date back to the late 1800s and early 1900s.
Weather News - May 22, 2019, 1:43:10 PM EDT
There is concern that the Gulf of Mexico may be the breeding ground for a second tropical storm to form before the Atlantic hurricane season officially starts on June 1.
Weather News - May 22, 2019, 11:32:34 AM EDT
Heading into the second week of the 2019 hurricane season in the East Pacific basin, there is the potential for a system to develop near the Central American coast.
Weather News - May 22, 2019, 11:30:54 AM EDT
In a circumstance similar to the iconic film Jaws, a great white shark -- one of the most predatory types in the world -- has been detected for the first time in an estuary on the Northeast U.S. coast.