HARLINGEN — A south-bound front out of nowhere was the culprit in late June, handing anguished Harlingen homeowners their second disastrous flooding event in 12 months.
Rainfall totals for the June 24 storm which sat and swirled this past summer varied wildly, but the heaviest precipitation fell in a line roughly to the west of I-69E from western Willacy County in the north, western Harlingen to the east, south of La Feria in that direction and the Hidalgo County line to the west.
Estimates put the rainfall totals in the hardest-hit areas at anywhere from 12 inches to 15 inches which occurred in around four hours as a mini- frontal boundary layer coming from the north stalled and belched rainfall measurable in feet.
An estimated 4,000 homes in the city were impacted by flooding.
Here’s what the city is doing to try to ensure the next heavy rainfall does far less damage.
Four scenarios
The International Boundary and Water Commission has floated four possible plans to address the flow of floodwater through the Arroyo Colorado, the main avenue to removing excess water from not only the City of Harlingen but much of the Rio Grande Valley.
City officials have lobbied for improvements to the Arroyo Colorado flow rate for at least 15 years, and if any good has come out of the major floods in back-to-back years, it is that federal officials are really listening now.
The city wants IBWC, which is responsible for maintaining the arroyo, to ensure Harlingen doesn’t become the retention pond for cities upstream.
The first option IBWC put forth is to basically stand pat, which understandably is not the preferred choice among City of Harlingen officials.
“A do-nothing type of alternative, which obviously is not something that we would like to see,” said Carlos Sanchez, an assistant city manager in Harlingen who also is an engineer. “Then the second alternative is to create a detention pond or offline storage which would benefit somewhat but it doesn’t provide for the restoration of the capacity of the Arroyo Colorado, so that’s not the ideal solution.
“Another option is to clear some vegetation which would improve some of the conveyance in the arroyo but again not restoring the full capacity,” he added. “The fourth one is to do vegetation clearance and sediment removal, which I see as the one providing the most benefit toward restoring the capacity of the Arroyo Colorado.”
Option No. 4
City officials have long disputed claims by IBWC engineers that the Arroyo Colorado maximum attainable flow rate at Harlingen is 21,000 cubic feet per second, or cfs.
At present, the Arroyo Colorado can only push water at 45 percent of the design discharge capacity, or about 10,000 cfs. But IBWC officials insist dredging the shallow arroyo and clearing vegetation should be enough to restore a 21,000 cfs flow rate.
Clearing vegetation and dredging — at an estimated cost to IBWC of between $8 million and $10 million — would occur on a six-mile stretch of the arroyo beginning where it flows under U.S. 77 Sunshine Strip near McKelvey Park downstream to near the Port of Harlingen.
“Alternative number four would be dredging of up to 3 feet of sediment that’s built up over the years in what I consider to be the pilot channel, the center where the water is typically conveyed,” Sanchez said. “Part of that is to clear up to 100 feet of vegetation, 50 feet on each side of the pilot channel. In areas where they cannot clear on one side, then they’ll go 100 feet on the other side. That all has to do with accessibility.”
The reason for four scenarios is that it is a requirement of the environmental assessment, which is being performed now by a consultant hired by IBWC.
“Our position is that the dredging and the removal of the vegetation will improve the capacity, the conveyance, but we disagree with IBWC because IBWC, in their statements, they’re saying it will restore at least that segment of the arroyo to 100 percent of capacity,” Sanchez said. “We disagree with that because, again, the arroyo is about 200 to 250, maybe 300 feet wide, in some sections, so they’re not cleaning the entire arroyo.
“Back when they started with 21,000 cfs capacity, at the time the arroyo was clear,” he added. “We have pictures where there’s nothing in there, and so if we’re not cleaning 100 percent (from top bank to top bank) how can we state that the capacity is being restored to 100 percent like it was 50 years ago?”
Dumping ground
The city has been proactive in finding ways to minimize the IBWC’s cost to dredge and clear vegetation along the arroyo, securing a dumping ground for the silt and mud from the dredging, called spoils.
“Part of the reason (the total cost) might be low is that we have worked, the City of Harlingen, has worked with IBWC to find a piece of property off of the Arroyo Colorado in close proximity to where they can transport and deposit the dredgings, the spoils,” Sanchez said. “That’s a big thing in itself because otherwise the transportation costs would probably add at least another 30 to 40 percent.”
The time-frame between the completion of the environmental assessment and actual work on the arroyo is unclear. But Sanchez said the assessment will be complete probably by February and will be submitted to the IBWC and then the U.S. Army Corps of Engineers.
Assuming the assessment finds no complications, “that will give us the green light to move forward or IBWC to move forward,” Sanchez said.
“It would be probably more like June, right at the start of hurricane season,” he added. “But to us, we see that as progress. The conversations that we’ve had with IBWC, and with our congressmen and senators in Washington, D.C., all that is generating fruit and the process is moving forward.”
Yet Sanchez and Harlingen officials are wary of a one-and-done mentality if the dredging and vegetation option is approved. They want IBWC to perform another flow rate test of the arroyo afterward to make sure 21,000 cfs really is attainable.
“We communicated to IBWC that once this clearing and dredging is complete, they need to come back in and do actual on-the-ground surveys of the cross-section of the arroyo, and then remodel or generate a new hydraulic model based on the existing conditions at that point,” he said. “And then we take it from there to prove what the actual capacity of the Arroyo Colorado really is.”
Ditches and drains
Almost all flowing water around here goes down into the Arroyo Colorado. City officials also are working on projects to improve how quickly it gets there.
They have been working with experts from Cameron County Drainage District No. 5 and the Harlingen Irrigation District to improve the flow of floodwaters headed to the arroyo.
“We have an inter-local agreement on two improvements to drainage ditch canals that convey water,” Sanchez said. “One is the 13th Street Drain Ditch located off 13th Street north and south of Loop 499, and the other one is the Dixieland Drain Ditch that starts off of Lincoln just west of Dixieland and heads south to the arroyo.
“Those are two major projects that we have submitted grant applications for FEMA (Federal Emergency Management Agency) to help us with excavation and widening and upgrading the road crossings,” he added. “We took it upon ourselves that we can’t wait for FEMA to come around and help us with those, so we’ve been asking for the funds for at least five to six years or so.”
Sanchez said the three entities are collaborating to fund the irrigation district to excavate and widen these huge ditches to increase their flow rates. Irrigation districts are self-governing agencies formed to provide irrigation and improve drainage from agricultural fields. In this case, the irrigation district already has the equipment to perform the work on the two ditches.
“We’re also increasing the pipe sizes and the boxes under the roadways to allow that water to move a lot more efficiently,” he said. “Between the county drainage district and the city, we’re paying about a half a million dollars collectively between those two drain ditches.”
Sanchez and other city officials are openly urgent about the need to address these systemic drainage infrastructure issues which contributed to the extent of damages from the past two summer floods.
Maybe these near-catastrophic flood events were just what the city needed after 15 years of making little or no progress with pleas for drainage help.
“Now is the time to capitalize on that because of the heightened level of awareness both from the public and elected officials and the different agencies … that brought a lot of those people to the table asking, ‘What can we do?,’” Sanchez said.
“We’ve gained headway.”
