City officials say changes to drainage system helped tame Hanna

By Maricela Rodriguez, Valley Morning Star

HARLINGEN — At least Hurricane Hanna was polite.

The Category One storm that rolled across the Rio Grande Valley on Saturday night and Sunday morning, as is usual with hurricanes, dropped its rainfall in lurching bands which allowed the city’s drainage system to keep up with runoff.

It was a distinct contrast to the major storm 13 months ago that dumped tons of rain on parts of the city in a short amount of time, leading to vast areas of damaging flooding.

“The one thing I will say is the rain was spread out over several hours, unlike June when we had 15 inches in three hours,” Harlingen City Manager Dan Serna said Sunday afternoon. “This time I think it was spread out over seven hours, which allowed our system to drain the water. Right now, the arroyo is running at 16.2 when back in June it was almost at 24 feet.”

By Maricela Rodriguez, Valley Morning Star

Serna said the city isn’t clear of any woods just yet and can expect some stress on the Arroyo Colorado as rainfall farther up the Valley enters the system on its way to the Gulf of Mexico.

“We continue to monitor that as well, because not only have we sent runoff from Harlingen, but also in the next couple of days, the runoff will come from the rest of the Valley, the McAllen, Mission area,” Serna said. “And some of that runoff will make it to the arroyo. Our expectation is that the arroyo will drain enough to allow for some of this additional capacity.”

City officials and engineers described the one-night rainfall in June 2019 as a 500-year event or even a 1,000-year rain.

Serna said it was satisfying to see that some of the changes the city made in the wake of the June flood — amid vocal criticism from some residents with flooded homes and businesses — seemed to be effective, despite more than 10 inches of rain falling on Harlingen courtesy of Hurricane Hanna.

By Maricela Rodriguez, Valley Morning Star

“I want to say a big shout-out to our drainage district (Drainage District No. 1) for constructing the two drainage retention ponds off of Montezuma just north of Route 499,” Serna said. “Those retention ponds provided a huge relief to a large section of the city.”

Courtesy Photo: Rachel Mann

“Unfortunately, there are areas in the Valley where the runoff wasn’t exactly what people were hoping for, but when you have the amount of rain that fell last night, a lot of rain, it’s a challenge trying to get it to run off,” he added. “In that respect, we were fortunate that our system worked well. The improvements to the 13th Street drainage ditch, the improvements to the 3rd Street drainage ditch and the retention ponds, and all the other improvements we’ve made over the past several months obviously provided us with a lot of relief.”

rkelley@valleystar.com