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Martindale pushes back on plan to bypass Blanco

Flood Mitigation
Friday, September 14, 2018

It’s meant to protect a neighborhood in San Marcos, but a project to reduce flooding from the Blanco River has created a multitude of concerns for people who live downstream in Martindale. 

The city of San Marcos held a public meeting Wednesday night at the San Marcos Activity Center to provide updates on options for federally-funded, short-term measures to protect Blanco Gardens from future flooding.

San Marcos received $25 million from the U.S. Department of Housing and Urban Development for infrastructure projects to mitigate flood damage in areas such as Uhland Road and Midtown. The Blanco Riverine project will use part of that funding, but there is a catch.

“We have to come up with a near-term solution to utilize those federal dollars by 2022,” said Eric Ratzman with Halff and Associates, an engineering firm working with the city on the project. 

Otherwise, the funding will be lost. 

 

The considerations

Ratzman reviewed the public meeting held in April to discuss potential options for flood mitigation on the Blanco. He said at that meeting, comments and questions from the public centered on several issues: Don’t make flooding worse in Martindale, consider the adverse effects of future development, consider the effects on existing river flows and natural patterns, and consider regional solutions.

Engineers added a detention option: a berm that would be a maximum of 3 feet tall that would protect Blanco Gardens from a 50-year flood and would be covered with native grasses. The berm would cost about $7 million, Ratzman said, and would require the acquisition of right-of-way along River Road. However, Ratzman said that the berm would raise water levels for about 1,000 other structures.

“We can’t do that,” he said. 

Instead, the engineers are looking at diversion options which, along with the berm, would protect hundreds of structures in the 50-year and 100-year floodplains. The route called Diversion 2 would take water from the Blanco across city-owned property that would accommodate a flow of 15,000 cubic feet per second and deposit the water in the San Marcos River upstream from the rivers’ confluence. 

The chief option the city is considering would be the construction of the berm, Diversion 2 and a complete bypass channel that would be 25 feet deep and 300 feet wide. Those projects altogether would benefit 473 structures in the 50-year floodplain and 836 structures in the 100-year floodplain, along with 573 structures in the 500-year floodplain for a cost of about $89,000 per structure.

“We can’t do buyouts for that amount,” Ratzman noted.

The completed bypass channel would run almost parallel to the proposed Farm to Market Road 110 between Interstate Highway 35 to just beyond State Highway 80. Its end point, where water would re-enter the river, would be downstream from Old Bastrop Road and upstream from Don’s Fish Camp. 

Ratzman said there would be a detention pond along the bypass channel to offset a slight water level increase in Martindale. The berm, Diversion 2 and bypass would create a level increase of 1 inch in Martindale, based on the flood of record (2015) — “which doesn’t sound like a lot, unless you live in Martindale,” he said. City-owned property would be used for a 30- to 40-acre pond to eliminate the 1-inch rise. 

 

Martindale’s concerns

At least a dozen Martindale residents spoke up after Ratzman’s presentation to voice their concerns. 

Mike McClabb, a member of the Martindale City Council, asked, “If your modeling is wrong and we get hammered, what do we get? … How are you going to guarantee us this bypass won’t affect us downstream?”

Another Martindale resident voiced concerns about debris traveling down the diversion or the bypass and creating issues and wanted guarantees that debris would not create more flooding. Yet another  asked if there would be measures taken to slow down the water velocity along the bypass so it doesn’t spill violently into the river just above Martindale. 

Tom Goynes proposed that to protect Blanco Gardens, the city should simply raise the houses that are currently in the floodplain and then, “Let areas that are going to flood, flood.”

Goynes made another suggestion — “For $25 million, we could get rid of The Woods Apartments” — that drew some applause from several people in the audience.

Another audience member from Martindale said the project is “definitely not helping the greater community.”

“Every time they build another apartment complex in San Marcos, we’re the ones taking the brunt of it,” he said.

He called for more to be done upstream to prevent flooding, but Assistant City Manager Laurie Moyer explained the funds are only for the city of San Marcos. She said the city agrees that more needs to be done regionally and the state needs to look at measures that could be taken.

“Like you all,” she said, “we feel like there needs to be a longer-term effort made.”

“You’ve got $12 billion sitting in the rainy day fund,” an audience member said of state officials, “and by God, it has rained.”

The options for protecting Blanco Gardens from flooding will be taken to the San Marcos City Council on Oct. 16 for direction in going forward with design. In the first quarter of 2019, Ratzman said, the city will hold another public meeting to discuss the outcomes of more detailed studies performed during the design process. 

The presentation about the Blanco Riverine project will be available on the city’s website, sanmarcostx.gov, in English and Spanish. 

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