The mechanics behind the daily rainbow in downtown Omaha
In October, the Bemis Center conducted a test run of The Rainbow project currently on exhibition.
Beginning Friday, the Bemis Center for Contemporary Arts will display natural rainbows above its building twice a day throughout the summer. Using information from a rooftop weather station, the temporary, self-contained rainwater-collection system will project 130 to 250 gallons per minute to produce a rainbow for 20 minutes.
Artist Michael Jones McKean tweaked the concept of The Rainbow: Certain Principles of Light and Shapes Between Forms over the course of a decade while he produced more than 30 other solo exhibitions. The large-scale installation now in place at the Bemis Center thanks to the Lindsay Corporation and other sponsors, can collect as much as 8,000 gallons from an inch of rain. "If we can collect this much from our little roof," said exhibition assistant Alex Priest, "you kind of ask why isn’t this more common?"
Twice daily, tanks will pump water to the roof of the Bemis Center, located at 12th and Leavenworth Street, to create The Rainbow.
The building's gutters pass rainwater through a basic filter before funneling into six daisy-chained 10,500-gallon plastic tanks. "You wouldn't believe what falls on a city roof," Priest said. "Dead birds, cotton that clogs the filters." Once in the tanks (which can balloon out as much as 4 percent as they fill), the water is stored until it's needed for one of the twice-daily rainbow events.
When it's time to produce a rainbow, water is pumped from the tanks to a UV filter that makes the water "nearly potable," according to Priest. "Nearly." He explained that the Bemis Center wanted the water that they spray back into the air to be as clean as possible.
A 60-horsepower pump shoots the water 130 feet in the air through three of nine nozzles on the roof. The commercial-grade irrigation nozzles can rotate up, down and side to side to spray water in configurations best suited to create a rainbow. "About 50 percent should land back on the roof," Priest said. "The goal is to reuse as much water as possible. Also, people in the parking lots probably don't necessarily want their cars wet."
Atmospheric scientist Dr. Joseph Zehnder of Creighton University used data on solar angle at different times of day to calculate a latitude and longitude values of a view footprint. These were input into Google Earth to determine the best vantage points each day. "For the rainbows in the morning, you'll have to be closer," said Bemis Center chief curator Hesse McGraw, "like at the base of the building. In the evening, you may have to be as much as a block away to see it properly."
The rainbows will be scheduled the day before they are displayed in order to get accurate information on the weather forecast, the position of the sun, and the expected cloud cover. Specific times will be posted on therainbow.org and on The Rainbow app, available for iPhone and Android.
Credits: Images of The Rainbow courtesy of the Bemis Center. First photo by Hesse McGraw, and second by Larry Gawel.