CEE Faculty Member Helps DelDOT Design Safety Grate for Storm Drains

September 30, 2005

by Diane S. Kukich, Research Administrator

Storm drains have long been a public safety concern, but the issue became particularly newsworthy in Delaware in September 1999, when two girls were swept to their deaths during a flood triggered by Hurricane Floyd.

The drains are necessary in an era of rapidly expanding development where natural drainage is interrupted. But headlines in the Wilmington News Journal during the five years after the tragedies caused by Floyd pointed to continued concerns about storm drain safety: "Deadly drain is still a danger." "Delaware slow to safeguard storm drains." "7-year-old sucked into drain, survives." "Father says grate couldn't come too soon."

Finally, in August 2005, a News Journal headline signaled good news: "DelDOT says it has developed a safer storm drain grate."

The new device, called the "Personnel Safety Grate," was designed by DelDOT in collaboration with Prof. Nobu Kobayashi of the Center for Applied Coastal Research at the University of Delaware. Kobayashi's contribution to the work was supported by DelDOT through a contract with UD's Center for Innovative Bridge Engineering. Both centers are housed within the Department of Civil and Environmental Engineering.

"Our overall goal," says Kobayashi, "was to develop a set of guidelines that would assist a competent engineer in designing a personnel safety grate with minimum adverse effect on the hydraulic performance of the stormwater pipe. We had to deal with the complexities caused by competing objectives: The grate must prevent people from being carried by stormwater into the pipe, but, at the same time, the pipe must be open to carry stormwater as efficiently as possible during storm events."

"We identified several major factors to consider in designing a safety grate upstream of a stormwater pipe that is determined to be hazardous," he continues. "These include the placement of the grate in relation to the pipe inlet, the orientation and inclination of the grate, and the orientation and spacing of the bars of the grate."

The term hazardous is currently used to refer to any pipe 12 inches or larger where daylight is not clearly visible when one is looking through the pipe. That criterion was reduced from 18 inches, after a seven-year-old child was sucked into a 12-inch pipe in July 2004.

According to DelDOT engineer Joe Ellis, Kobayashi's report was instrumental in providing guidance for developing a Standard Construction Detail for Personnel Safety Grates.

In developing the standard and coordinating with pipe manufacturers and fabricators, DelDOT is providing guidance to others, such as developers, as they also need to place PSGs in their hazardous storm water pipes.

Last year, DelDOT installed new Personnel Safety Grates over open-ended stormwater pipes in the Caravel Hunt, Pine Valley, Westover Woods, and Duncan Glen developments in New Castle County. DelDOT has also been refining stormwater safety in existing systems and incorporating storm water safety mechanisms into standard construction plans.

In addition to developing technical guidelines for storm drain safety grates, Kobayashi's report recommended that a holistic approach be adopted, with the participation of various agencies, civic groups, and media.

"Accidents can be minimized if children and adults know the danger of playing in water in the vicinity of stormwater pipes," he says. "Active participation of the public through stream clean-up and elimination of household litter in backyards and roads helps reduce debris clogging on grates. Public education, such as public service announcements in local radio and television programs at the beginning of and during the hurricane season, should be part of the overall effort in promoting safety near stormwater pipes."

DelDOT's Ellis agrees with Kobayashi about the importance of an educated public with regard to storm drains. "We're very pleased with the new grate design," he says, "but I can't stress enough how important is that residents not take this problem into their own hands. DelDOT is placing grates over the upstream opening to the drains, but it is very dangerous to block the outfall end of a pipe. If a person gets into the system, they are trapped. It also creates some serious maintenance problems."

This safety grate, located in Hickory Woods in New Castle County, was one of several that were installed before fall 2004 but were evaluated by Kobayashi in light of the findings in his report.