Concerns about protecting inlets and storm drains don’t stop when construction stops.
To help meet Honolulu’s stormwater management goals, the engineering firm Oceanit—an engineering and technology firm in Hawaii—contacted Terry Flury of United Storm Water in October 2014 to ascertain how his company’s Wing-Gate Automatic Retractable Screen (ARS) might help.
The Wing-Gate ARS opens horizontally like a door, notes Flury, the system’s inventor. “It’s flow directional; that means when water comes down one side of the curb, this device opens up. It pivots from where the flow is coming from.”
The device is constructed of stainless steel with three-quarter-inch perforated holes for a 51% surface opening.
Mounted at the center of the curb drain opening, the Wing-Gate ARS is installed with a 1- to 2-inch gap at the top of the screen for overflow bypass. It remains in a closed position during the dry season or low water flow, and the retained pollutants can be removed using routine street sweeping.
“It remains closed under a stainless steel torsion spring that keeps the street sweepers from pushing debris into the curb openings, so it’s not locked to the curb,” says Flury. “It’s free to open, but the street sweepers pushing debris by it will not open it up.”
During periods of heavy water flow, the spring-activated wings open laterally to prevent flooding that may otherwise be caused by accumulated debris on the screen. The wings close automatically as a storm subsides.
The Wing-Gate ARS is set to open at about 3 inches of curb water flow. “It opens up at one end under spring pressure, which is about 2.5 pounds of pressure on the face of the screen itself,” says Flury. “It will only open up as much as the flow, so if the flow is minimal, it’s not going to open up much.”
During a significant weather event, the ARS will open up as much as needed to accommodate debris such as large palm fronds or whatever is coming down the curb opening, says Flury. “It can actually push the screen opening even further to allow everything in so it doesn’t clog up the front, and it allows the water to drain.
“The ARS device keeps the big stuff from going through, and there are other devices that keep the smaller items such as a cigarette butt from entering the storm drain,” says Flury. “In essence, ARS works like a construction barrier because it keeps out everything from flowing into the catch basin.”
Wings can be manually pinned in the open position as needed during catch basin cleaning or extreme storm conditions. Gates with double or single wings can be installed in series based on catch basin length and flows to the site. The ARS can be used in conjunction with various other storm drain filters.
The Wing-Gate ARS is designed to be “very efficient” when there is trash in front of it, adds Flury. “The whole idea is to keep debris from entering the catch basin,” says Flury. “During a big storm or rain event—especially a big first-flush event—it’s absolutely 100% necessary that the screen opens up and lets everything in. Otherwise it’s going to cause some pretty bad street flooding and lead to some liability issues like you would not believe.”
Honolulu’s storm drain system was presenting some issues that required mitigation, notes Flury.
“They wanted to keep their oceans beautiful, and because there are so many trees and leaves, they had a tremendous problem with their catch basins being impacted with a large amount of green waste,” says Flury.
“Some of the lateral pipes they have that collect from drain to drain were too small,” he adds. “They would clog up very easily, backfill with water, and initially cause a lot of flooding. They wanted to make sure they eliminated their flooding events, and they also wanted to clean up the trash and keep it from entering the ocean.”
Flury says he was at first hesitant about putting anything in the curb openings because the height of curb openings in the state of Hawaii range from 5–6 inches, “which is very small compared to what we have in California. If you put anything of this type in curb openings that small, you risk the chance of street flooding if any debris gets caught in front.”
United Storm Water developed a screen to work for Hawaii’s needs after Oceanit asked the company to pilot test seven Wing-Gate ARS in the streets of Salt Lake, a suburb of Honolulu. The city tested them by opening a fire hydrant to make sure they would open up during a big storm. The screens passed the test.
A subsequent severe weather event with torrential downpours provided a “reality check,” says Flury, with the ARS system performing as designed, opening up and not allowing the streets to be flooded.
In March, Honolulu awarded United Storm Water a contract to retrofit inlets with 400 ARS units. The work will take place in the fall.
“This design was implemented to keep trash from entering the basin; it’s primarily devised to keep the street sweepers picking up all of the trash instead of pushing it into the curb openings,” says Flury. “That’s why the screen was developed in the first place.”
Having the screens in front of the basin, rather than using devices to trap debris within the basin, reduces catch basin cleanouts by about 50% per year, says Flury. Cities typically clean out catch basins three or four times a year to prevent flooding during a significant storm, he adds.
“With the ARS devices in place, you’re looking at the very maximum of two times per year,” he says, adding that while it cuts maintenance costs, it also enables street sweepers to work more efficiently by picking up more debris as opposed to pushing it into the basin.
Flury says he was led to invent the Wing-Gate ARS because he saw that when existing devices opened vertically, “they seemed to work really well when there was no trash involved. The minute trash became a factor, these devices plugged up and liability issues came into effect; streets would flood.”
Although there are different versions of screens on the market, “nobody thought about the idea of a flow-directional type of system that would open up more like a door, which is more efficient because it can open a tremendous amount and really be able to clear large volumes of water and trash and at the same time have the ability to close up and keep debris out during the non-rain events,” he adds.
United Storm Water performs the system installation.
“They have to be put in just right and calibrated,” says Flury. “In order to have a warranty on these items, we have to do it ourselves to be able to back up that warranty.” The warranty is one year for parts and three years for a working system.
There are instances in which the ARS should not be used, points out Flury. “Usually we won’t put anything in that’s 3 inches or less,” he says. “Things can plug up quickly. If a city only does street sweeping once a month, that’s not going to do it. That’s going to cause a problem.”
