San Marcos City Council discussed strategies aimed at mitigating future flood damage, including construction of a Blanco River bypass, at a workshop April 25.
The bypass project would create an alternate route for the Blanco River in heavy storm situations. The bypass would take the river east of its current alignment before rejoining it with the San Marcos River.
According to a 2007 study by the city of San Marcos, the bypass project would cost more than $60 million to build. Land acquisition was not factored into that cost estimate. The city has not committed to the project yet and is awaiting the completion of a study by the Army Corps of Engineers looking at the bypass’s feasibility.
If the Corps of Engineers study determines the bypass is the best way forward, construction could begin as soon as winter 2018 or early 2019, according to a presentation given to council at the April 25 meeting.
If the project moves forward it could be funded by the city, the Corps of Engineers, the Guadalupe-Blanco River Authority and other entities.
City Manager Jared Miller said the city will likely look to tackle projects in the short term while it awaits the findings of the Corps of Engineers’ study.
“Our best value position is going to be in some type of diversification—a range of projects that we’re going to take in the short term as we analyze larger projects, understanding that the [effect those short-term projects have on flooding issues]may not be as big on the smaller projects, but taken together they’re going to have a huge effect,” Miller said.
Council discussed short-term fixes to the city’s drainage system at I-35 and Aquarena Springs Drive, I-35 and River Ridge Parkway and at Linda and Sherbarb drives in Blanco Gardens.
The city is also considering buying out flood-damaged properties in the Fairlawn neighborhood.
“Fairlawn is a known repetitive loss area from flooding and was identified for potential buyouts in the Hazard Mitigation Grant application that was submitted for funding late last year,” said Richard Reynosa, senior project engineer for the city, in an email. “If funding for buyouts becomes available and the direction is given, Fairlawn would be one of the recommended areas.”
Flood ordinance revisions
The city will consider amending its flood ordinance to require new structures be built either 1.5 feet or 2 feet above the base flood elevation (BFE)—the lowest level that that the Federal Emergency Management Agency, or FEMA, determines structures can be built at. The current ordinance requires new structures to be at least one foot above that level.
City Council directed staff to go forward with the 2-foot recommendation during public outreach. A formal ordinance will be brought back to council for future consideration and adoption.
City Council Member Scott Gregson said the city needs to closely examine development patterns in San Marcos and cities upstream of San Marcos on the Blanco River. As areas get developed and concrete gets poured over the ground—for roads, sidewalks and driveways, for example—where grass once was, less water is soaked into the ground during heavy rain events. That water instead falls on the concrete and eventually finds its way to the river.
Gregson said he was concerned that as more development occurs in San Marcos and nearby communities, the base flood elevation—or the lowest level that FEMA determines structures can be built at—will continue to rise.
City Engineer Richard Reynosa estimated the BFE in the city has risen as many as three feet in the past three decades.
Gregson said discussions about requiring new structures to be built at or above the BFE determined by FEMA ignore the issue that the BFE continues rising.
“We’re dealing with the symptoms,” Gregson said. “We’re not dealing with the problem.”
A new home built at or above the BFE might be below FEMA’s requirements after a few years due to continued development and impervious cover.
Gregson proposed the city look to open discussions with nearby communities in order to determine what developments near the Blanco River may affect the BFEs in the city.