LAGOON

Ian deluge sure to 'shock' Indian River Lagoon; heavy rain and runoff bad news for estuary

Jim Waymer
Florida Today
A group on vacation from Arkansas in early July of 2022 was heading out into the Banana River in search of manatees and dolphins. The group was taking a tour through the Thousand Islands with Cocoa Beach kayaking. Biologists say Hurricane Ian could further harm wildlife in the lagoon.

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No matter what degree of havoc Hurricane Ian leaves in its wake in Brevard County, what is certain is that the huge amount of rain heading our way will be enough to deliver more bad news for the Indian River Lagoon.

The heavy runoff from the storm will come as a blunt shock to an already overwhelmed estuary, with vastly shrunken seagrass beds and a weakened and dying manatee population

Forecasters expect only about three feet or a few more of storm surge, so beaches are likely to be mostly in the clear. But Ian's deluge — projected at six to 10 inches or more — could put already stressed manatees, dolphins and other lagoon life in peril, in the wake of a record sea cow die off.

"Intense storms like hurricanes are shocks to coastal ecosystems," Duane DeFreese, executive director of the Indian River Lagoon National Estuary Program, wrote in an email. "They can produce a whole range of stressors that may continue to have impacts for weeks, months and sometimes years after the storm passes."

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Tropical Storm Fay and heavy rain events in the years that followed helped set the stage for an algae "superbloom" that ultimately killed off more than half the Indian River Lagoon's seagrass, and 90% of its coverage area in some regions of the estuary.

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Those rains carried mass influxes of nitrogen and phosphorus from fertilizers, septic tanks and other sources. And heavy rains already have wrought multiple large-volumes spills of raw sewage along the Indian River Lagoon this year, even though the region has been under a moderate drought conditions.

Improvements offset by growth

In the five years after Fay hit the Space Coast in 2008 and lingered here for days dumping vast amounts of rain, the county spent $30 million on 13 stormwater project areas from north of Titusville to Grant-Valkaria.

During the same period, Brevard added almost 43,000 residents, resulting in more rooftops, driveways and roads for water to run off. So the net effect on flood risk, to some extent, remains a wash, some experts have warned.

Stormwater, sewage and agricultural runoff are the lagoon's worst enemies, biologists say. By the mid 1990s, a state law phased out most sewer plant discharges into the lagoon, solving one of the estuaries biggest problems, or so scientists thought. But the lagoon failed to improve as much as they’d expected, and runoff was the reason. 

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Storms send thousands of gallons per second of cloudy, contaminated water careening down Canal 1, south of Port Malabar Road, toward the fragile Indian River Lagoon.

This eight-mile, 100-foot-wide canal was cut in the 1920s, draining more than 100 square miles of historic St. Johns River floodplain so its fertile soils could be farmed.

But the canal — also called C-1 — linking the St. Johns to the Indian River Lagoon, often pushes too much fresh water, too quickly into the lagoon. That lowers the lagoon's salt content and kills marine life. The cloudy water then blocks sunlight that seagrass needs to grow.

Canals like C-1 act as artificial arteries that drain freshwater lakes and rivers to coastal waters. So water managers say the so-called C-1 re-diversion project — which aims to mimic the St. Johns River's historical flow to the north rather than to the lagoon — and decades of other improvements to the Melbourne-Tillman Water Control District now better protect the lagoon from stormwater onslaughts.

But what flows from our yards and streets to our canals also determines the lagoon's fate, biologists have warned.

Long-term impacts from such heavy rain events as Ian threatens are hard to predict, DeFreese said.

As of Sept. 16, at least 694 manatees already have died this year, most presumed from starvation after long-term seagrass loss. That compares to 946 during the same period last year, in which a record 1,101 manatees died.

"Healthy ecosystems will have more resilience to these shock events than systems already under significant chronic stress like the IRL (Indian River Lagoon)," DeFreese said. "It’s like “adding insult to injury.”

La Niña is partially to blame

La Niña has helped keep the Space Coast drier than usual this year. La Niña is a cooler-than-usual pulse of water near the equator in the Pacific Ocean — the flip side of El Niño, which is warmer-than-usual water in the same region. Both patterns, which happen every several years, alter global climate patterns and have implications for hurricanes.

What if Brevard got hit with 50 inches of rain: Imagine the unimaginable

La Niña typically results in warm, dry conditions in Florida and lacks the shearing winds, so tends to coincide with more active hurricane seasons.

So far, La Niña has lived up to its tendencies, keeping the Space Coast drier than usual. Melbourne saw 30.36 inches of rain over the past six months, or 5.7 inches below normal for that period, based on 73 years of data, according to the Southeast Regional Climate Center, based in Chapel Hill, North Carolina. But in the past two months, the city has almost caught up to normal, with 12.4 inches of rain, the 11th wettest two months on record.

In part, the seasonal slowing of the Gulf Stream and the moon's cycle are to blame for the higher waters on which Ian will ride in on near Brevard.

When the Gulf Stream slows, its warmer water bunches up closer to the coast, raising sea levels. Sea level rises up higher than the lagoon's inlets, so lagoon water can't escape out to the ocean.

Mean sea level is at a minimum in June, when the Gulf Stream is at maximum flow. As the Gulf Stream slows to its minimum flow in October, mean sea level reaches a maximum.

Prevailing winds drive currents that cause water either to build up in certain areas of the lagoon or flow elsewhere. Daily tides only influence the immediate areas near openings to the ocean, such as Sebastian Inlet.

Then there's the pull of the moon, which keeps the seasonal tides and the lagoon high.

Less from Tropical Storm Fay

In 2008, Tropical Storm Fay dumped more than two feet of rain on the lagoon in about a day.

Boating and fishing advocates for years had tried to get the U.S. Army Corps of Engineers to keep Canaveral Lock open to cleanse pollution from the lagoon. That’s been tried before, with costly consequences. 

To reduce flooding during Tropical Storm Fay in 2008, the Corps left open the locks, which connect the Banana River to the Atlantic Ocean via Port Canaveral. The port’s main shipping channel filled with sand and had to be dredged.

Then after heavy rains in March 2011, scientists began to notice a widespread algae blanketing the Banana River. The plankton soon enveloped Merritt Island and spread beyond what biologists had ever seen, stretching 70 miles south to Melbourne.

They dubbed it the “superbloom.” It was unprecedented. The bloom would nearly wipe out the lagoon’s seagrass, ultimately killing a combined 73 square miles of the vital bottom plant — the linchpin of the marine food web. Other casualties included hundreds of manatees, pelicans and dolphins.

"For harmful algal blooms, blooms in progress can be disrupted by wind, waves, changes in salinity, and changes in water temperature," DeFreese noted.

Ian's heavy wind and rains, runoff will bring increased nutrient and pollutant loading to feed existing lagoon algae blooms from failing sewage treatment plants and other land sources.

"It very hard to predict algal bloom outcomes after a storm," DeFreese added. "But an intense hurricane like Ian is not good news for the IRL."

Water levels in the lagoon are already seasonally high, he noted, adding that Ian's winds and waves will increase the lagoon's cloudiness and shoreline erosion. 

The combination of changing salt levels, temperature and high nutrients make the lagoon more vulnerable to blooms of algae species that could thrive in the new conditions, he added.

What might Ian do in Brevard?

Surge: Potential for storm surge flooding greater than 1 foot above ground

Flooding: Six to 10 inches of rain with locally higher amounts. Localized inundation with storm-surge flooding mainly along immediate shorelines and in low-lying spots, or in areas farther inland near where higher surge waters move ashore. Sections of near-shore roads and parking lots become overspread with surge water. Driving conditions dangerous in places where surge water covers the road.

The beaches: Moderate beach erosion. Heavy surf also breaching dunes, mainly in usually vulnerable locations. Strong rip currents.

Boats: Minor to locally moderate damage to marinas, docks, boardwalks, and piers. A few small craft broken away from moorings. 

Source: National Weather Service, Melbourne

Jim Waymer is an environment reporter at FLORIDA TODAY. Contact Waymer at 321-261-5903 or jwaymer@floridatoday.com. Or find him on Twitter: @JWayEnviro or on Facebook: www.facebook.com/jim.waymer

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