HARLINGEN — One of the biggest storms in decades is teaching engineers lessons.
City and county officials are planning some of their future drainage projects based in part on what they’re learning about the unforeseen storm that dumped more than 12 inches of rain in a four-hour period Monday night and early Tuesday morning.
“The information we’re gathering helps us identify points we can prioritize for drainage improvements,” Assistant City Manager Carlos Sanchez, a hydraulics engineer, said Friday as he set up pump sites in the Secluded Acres subdivision on the city’s hard-hit north side.
“We’re doing a lot of documenting to record water levels to help us create a design for capital infrastructure improvements,” he said. “All of this is helpful in better preparing us for a storm this size.”
Meanwhile, Alan Moore, general manager of Cameron County Drainage District No. 5, was inspecting the drainage system that draws floodwaters from areas stretching from Palm Valley to Harlingen’s northeastern side.
“We’re always trying to improve,” Moore said from his office. “We have a five- to six-year-plan. We’re re-examining those. Some will be popular and some won’t — some aren’t so pretty and kind of expensive.”
Along the city’s northern edge, floodwaters rushed into low-lying areas such as Secluded Acres and nearby Spanish Acres, Sanchez said.
He said flooded areas included the low-lying Parkwood subdivision and some neighborhoods near the Arroyo Colorado.
Those low-lying areas, he said, tend to flood because they lie at lower elevation that the canals built to drain floodwaters.
“We’re looking at localized flooding in different areas,” Sanchez said. “That can help identify weaknesses in a storm sewer system.”
As part of an emergency response plan, he is plotting sites at which to operate pumps to help more quickly drain floodwaters.
“We’re identifying locations to place portable pumps to expedite the flow of water,” he said.
City Manager Dan Serna has described the storm as having a frequency of a 100- to 500-year rain event.
However, the city’s drainage system was designed to handle 100-year storms, he said.
“We realize our system does not have the capacity to handle the intensity” of storms having more than 100-year frequencies, Sanchez said. “We’re going to have localized flooding. These projects are intended to minimize flooding.”
Sanchez said the construction of a drainage system designed to handle a major storm event would be costly to undertake.
“It’s not economically feasible to design for a storm of this magnitude,” he said. “It’s low-probability and you’re talking about pulling out the existing system and replacing it with larger pipes. The lay of the land is pretty much flat so you’d have to put a lot of bigger pipes, drainage boxes and bridges.”
In 2008, the same year Hurricane Dolly flooded parts of town, officials drafted the city’s drainage master plan.
As part of the plan, the city launched $13.4 million worth of projects after landing $6.49 million in grant money while dipping into the general fund budget or borrowing to come up with $6.9 million.
From 2012 to 2014, the city worked to complete drainage projects in the Buchanan, Hays and M Street area, the Jefferson Avenue area and the Third Street area.
Last October, officials launched a study aimed at designing a $1.5 million project to curb flooding in an area along Ninth and 13th Streets.
Now, officials are planning about $10 million in upgrades to its winding network of pipelines, ditches and canals.
“We have identified projects and we continue to seek funding,” Sanchez said. “The information we’re gathering is going to be very useful.”