On June 9, a stormwater pond near Port Tampa Bay in Florida began to empty itself, independent of human interaction.
The water level in the pond near Tampa's port district dropped around 10 in., emptying almost 70,000 cu ft of water into Tampa Bay. It wasn’t quite enough to catch the 2.8 in. of rain that fell in one hour on June 10, but Jeff Littlejohn, president of National Stormwater Trust (NST) considers it a success for the group’s new Smart Pond technology.
“This is an indication of an optimum scenario,” he says. “The pond’s at the right level, a rain event is coming, the pond says it’s time to open, it opens, it discharges and then the next day when that big rain event happens it almost exactly captures all of it.”
The pond is fitted with Smart Pond technology, developed by OptiRTC and installed via an agreement with the Florida Dept. of Transportation.
An internet-connected computer responds to National Weather Service forecasts, calculates how much water the pond is expected to catch, and empties that amount ahead of an expected rain event without any human interaction. When no rain is in the forecast, the ponds will hold an optimal level of water for water quality treatment purposes.
“What Smart Pond technology means is we are using real-time weather forecasting and automated controls to actively manage stormwater ponds,” Littlejohn says. “In between storms, that pond is actively managing its water levels to maximize water quality treatment.”
The state agreement with NST provides access to thousands of ponds in Florida, Littlejohn said, with plans to actively develop 12 to 20 more ponds in 2022. The DOT and company are working in the Tampa Bay area and will expand toward Orlando. The pond near Port Tampa Bay is NST’s sixth, but its first with the agency to be fully automated.
“What’s really going to be exciting to see is when we have multiple ponds converted to Smart Ponds in a given region,” he says. “We could have entire neighborhoods saved from flooding if you have enough ponds retrofitted that could be actively drained down to prevent a flood.”
Comparing modeling for the original pond designs and models for the retrofitted Smart Ponds shows 44% more water quality treatment and 84% more flood attenuation volume, Littlejohn said.
The agreement allows NST to use its technology in state DOT ponds, while the agency reaps the benefits. Beneficiaries are entities such as Port Tampa Bay, he said, which can purchase water quality treatment in a Smart Pond instead of building its own pond.
Littlejohn explains that the more residence time-how long the water spends in the pond-the more nutrients like nitrogen and phosphorous are removed through uptake in vegetative material, or by bacteria in the water and soil.
"The more residence time in the pond, the more effective those removal processes are," he says.
Water released by ponds goes into the local watershed. For the three ponds already working in the Tampa Bay area, that is either directly into the bay, or into canals and ditches that lead to the bay, he says. For other ponds at Babcock Ranch near Fort Myers, Fla. that's the Caloosahatchee River.
Patrick Blair, Port Tampa Bay, vice president of engineering, sees in Smart Ponds a middle ground between conventional ponds that take up lots of land and expensive vaults that store lots of water. He also sees an option that could have other benefits for the port, such as opening up valuable acreage.
“Ponds with automated valves and remote systems to control volume to increase capacity are substantially able to hold more water and treat more nitrogen than I would be able to on my site,” he says.
At $200,000 to $300,000 per retrofit, Smart Ponds are cheaper than the $650,000-per-acre-foot vaults but more expensive than conventional, passive stormwater ponds.
The technology is creating a better net gain for the environment with more nitrogen treatment, and is increasing the amount of usable space for Port Tampa Bay, Blair says.
The port has more than 20 stormwater ponds over its 5,000 acres in a state that sees 100 rain days a year, including roughly 48 in. in the period from May through September.
In locations where the port is expanding and land values are high, the smaller-footprint Smart Ponds free up needed space for product and materials, another strategy to help ease ongoing supply chain issues. “We get more space for less dollars in our high, heavy-load areas,” Blair says, adding that it also is designed to improve over time. In the case of the June 10 storm, the pond was being maintained at 190,000 cu ft of water, but at the peak of the storm, reached 226,000.
A tipping bucket rain gauge attached to the system measured rainfall, with all data gathered set to improve the modeling at that particular pond.
It also may have rained more than what the forecast called for, says Mark Thomasson, NST executive vice president and design engineer for the Smart Pond technology, who works with OptiRTC that manages the software.
“The model is our best guess on that runoff coefficient,” he says. “What we’re going to get after a few months or several rain events is what the actual runoff coefficient for the basin and how the pond reacts to that.”
In the case of the pond at Port Tampa Bay, missing the mark on the low side is OK, but a pond in a flood-prone neighborhood would need to be managed with a more conservative model, Littlejohn says.
The Southwest Florida Water Management District and South Florida Water Management District manage large-scale canal systems and flood controls systems that use weather forecasting, remote-controlled valves and pumps to manage flood control systems, he says. A similar program is being developed in Maryland.
But, Littlejohn says there is no equivalent program in the country where a state DOT has granted access to all of its ponds to be retrofitted by a private entity.
“Our hope is widespread water quality benefits and widespread regional resilience benefits—flood control benefits,” he says.