Stormwater utility protects against 100-year storm, definition of storm differ

El Paso’s stormwater utility officials have said they build storm prevention facilities, such as pumping stations and drainage canals to withstand 100-year storms. But there are different definition of such storms.

Stormwater utility officials have said they define a 100-year storm as three inches of rain in a 24-hour period.

“Any storm that happens – there’s a 1% chance it can increase that level,” said El Paso Water Utilities President and CEO John Balliew on Wednesday.

The National Weather Service defines the 100-year storm in the El Paso region differently, however.

“If you look at government agencies, a 100-year rainfall in 24 hours would be almost four inches,” said John Faucett, a Meteorologist with the National Weather Service.

Faucett said two inches of rain in 24 hours is considered a five year storm.

“We’ve had several occurrences of two inches in 24 hours in the last few years,” said Faucett.

Faucett said a 100-year storm does not mean you only get that much rain every 100 years.

“When you look at a long term average, thousands and thousands of years and you average out,” Faucett said. “Maybe in a thousand years, you’ve had ten of those and it averages out to every hundred years but two of those could have been in the same week.”

The big storm in late September yielded about six and a half inches of rain in Northeast El Paso. Faucett said they consider that storm a 1,000 year storm.

Balliew said it’d be too costly to build facilities to withstand that much rainfall.

“I don’t think there’s any city in the southwest that would do that,” Balliew said. “The more level of design, the bigger the facilities and the more they cost. The city is already developed, so when we build facilities, we have to go areas that are already developed, buy pieces of property, occupied homes and what not so you have to balance the level of protection we’re providing and the cost and impact on the community.”

Utility officials said they define the one hundred year storm by averaging rainfall throughout the city.