Wind blamed for interrupting natural bay flushing
Warwick’s four licensed beaches have been closed due to high bacteria levels for a combined total of 60 days this summer, leading to frustration for Michael Rooney.
“Obviously, people go down to the beaches to get relief from the heat,” said Rooney, deputy director of Warwick Parks and Recreation Department. “It is such a warm summer and people are getting frustrated. And I understand.”
The Rhode Island Department of Health (DOH) monitors the state beaches’ bacteria levels and will close a beach for swimming if the bacteria level, particularly the level of the indicator organism Enterocci, is above 104 colony forming units per 100 milliliters of water.
Oakland Beach has been closed a total of 29 days, re-opening most recently on Tuesday afternoon. Conimicut Point Beach has been closed 13 days, City Park has been closed 12 and Goddard Memorial has been closed six.
For comparison, all four beaches were closed a combined total of seven days in all of summer 2012.
So what makes summer 2013 so different?
University of Rhode Island Graduate School of Oceanography student Christelle Balt believes a combination of high runoff events and a south wind is to blame for the consistency and length of the storm.
Balt has been studying the movement of the ocean for five years at URI, particularly of Narragansett and Greenwich Bays.
With the help of her advisor, Professor Chris Kincaid, Balt has used both numerical models and direct field measurements to prove her theory that the direction of the wind will have an effect on the way the bay flushes out.
Demonstrating with a computer model that provides an idealized situation, Balt is able to visualize how both surface and bottom water and any particle in the water would flush out of the bay depending on varying types of wind.
“Now you know the effect that type of wind will have on the water system,” said Balt.
“You can kind of play God a little bit,” said Kincaid when describing the ability of the user to determine tides, winds, river flow, etc. in these models.
When the model is played out with the wind shut off, the particles (which could be bacteria) will flush out of Greenwich Bay in less than 10 days in all areas, meaning the northwestern, southwestern, northeastern and southeastern portions.
However, if Balt changes the wind to be a continuous wind blowing from south to north, it took 30 days to flush the western portions of the bay.
And that is if there is not continuous contamination.
And Balt has field data that brings her to the same conclusion.
“You can validate that the model is giving you the correct data,” said Balt.
Data she collected in 2010 from water current meters located in Greenwich Bay shows there was very little movement in bottom water when winds were blowing toward the north.
When winds blew toward the east, there was great movement and flushing.
The same can be said for Narragansett Bay.
“On the scale of Narragansett Bay, when the wind is to the north, it has this stalling tendency,” said Balt.
She explained that bottom water in Narragansett Bay tends to flow toward land and surface water south toward the ocean. However, when there is wind blowing north, it forces the surface water in and stalls the bottom water.
As for 2013, Balt has not modeled her data just yet but has been able to compare heavy storms (a large runoff event), northern blowing wind and beach closures. She found they coincide.
Using Oakland Beach as an example, that particular beach was closed for swimming on June 25 for 15 days until July 10.
According to the United States Geological Survey of water discharge from the Pawtuxet River in Cranston, there was a discharge between 600 and 700 cubic feet per second during that same period.
Also, the Physical Oceanographic Real Time System calculated wind vectors at Quonset Point to be blowing toward the north for roughly the same period of time.
Balt believes these large runoff events put the increased amount of bacteria into the bay and the northern blowing sea breeze prevents natural flushing, essentially trapping the bacteria in the bay for a longer period of time.
The same data shows that in the month of June, Pawtuxet River discharge reached nearly 2,500 cubic feet per second in early June and wind has been blowing to the north periodically this summer. Balt says this data coincides with the first beach closures seen this summer.
Dara Chadwick, the public information officer for DOH, admits flushing is an issue.
“We don’t see as much natural flushing in the upper bay,” said Chadwick.
Despite these closures, there is still no word on what is causing the increased level of bacteria at these beaches.
“We’re working with Department of Health, Department of Environmental Management, the Highway program and Warwick Sewer to find out what’s going on,” said Rooney, but there is no idea yet.
“No direct source of contamination has been determined,” said Chadwick, saying it is a combination of runoff from the streets, pet waste, storm water, sewage and even seaweed keeping the bacteria alive in the bay.
“There is nothing we can pinpoint,” said Chadwick.
Professor David Smith, who is also the associate dean of the Graduate School of Oceanography, said the frequency of testing may also lead to extended closures.
Smith has studied naturally occurring bacteria in the water, but has also done work regarding the bacteria that enters the bay from runoff or other sources.
Chadwick said the upper bay is tested two or three times each week. Smith explained that it takes time to get the results of a test, so the water levels could be acceptable before the results even come back.
However, Smith pointed out nothing can be done to change that fact because it is the nature of the testing.
Smith also said this form of bacteria will eventually decay away in the water.
“That bacteria is designed to be in your body or animals,” said Smith. “They have to be continuously introduced into the bay.”
He said the key to preventing these large spikes in bacteria levels would be to catch runoff before it makes it to the bay.
That can be done through things such as watershed catchments, which catch rainwater on the streets and deposit it in the soil, or green roofs.
Green roofs have plants keep rainfall retained on the rooftop.
“[The key is] having more of a buffer zone,” said Smith, explaining that the bacteria can be taken in by other things such as soil or plants instead of going into the beaches.
The Combined Sewage Overflow Abatement in Providence, which is a six-mile stretch of underground storage tunnels and other features that will reduce overflow of storm water and sewage during heavy storms, is helping.
“That’s come a long way with helping our overflow situation,” said Smith.
Balt explained that system could also benefit Greenwich Bay because water from the Providence River tends to want to travel to the west, toward our bay. The cleaner that water is, the better for the bay.
“You can see contaminants from [Providence] going into Greenwich Bay,” said Balt.
Smith also pointed out that this heat wave could help with the bacteria problems. With no rain events, less bacteria will travel to the bay and UV radiation from the sun will kill the bacteria currently in the surface water.
“Assuming you are not adding more,” points out Smith.
Rooney may be frustrated with the closures, but he knows monitoring the quality of water is important.
“We are looking out for the welfare of the people,” he said. “We are also mindful of the fact that it is hot, and people want to go swimming.”
Chadwick said if a beach does close, her department tries to re-open the beach as soon as the levels are acceptable.