New FEMA flood maps raise construction heights along San Marcos River

Oct. 22--SAN MARCOS -- Fast growth can have dramatic consequences, especially when it comes to flood control. As Central Texas cities continue to expand, they need to give greater consideration to flood control when approving new development.

The city of San Marcos learned this lesson the hard way during the recent Memorial Day floods, when within a matter of hours a raging downpour caused flooding that killed 12 people, devastating communities along the Blanco River and causing millions of dollars in damage.

Despite a history of flood events, the city has continued to approve dozens of projects every year in the 100-year flood plain, a federally designated area which has a 1 percent chance of experiencing a major flood in any given year. According to American-Statesman reporter Sean Collins Walsh, city officials describe their approach as "pretty much on average" compared with other cities in Texas.

But San Marcos's growth is anything but average. And the human and financial costs of not taking a more-conservative approach to floodplain development in that city could be substantial.

Climate change appears to exacerbating the boom-bust rain cycle that characterizes Flash Flood Alley. If you combine that with the pressures of rapid population growth, arguments for not holding development to higher flood-control standards are harder to make. Floods like the one Central Texas experienced in May are not examples of an "extreme situation," as some residents suggest. Rather, they are the new normal, and as such, regulation by the City Council and city officials must be more strategic.

Central Texas floods may seem random, but in fact, such events are largely predictable, according to University of Texas expert David Maidment.

To make his case, the civil engineering professor points to the 2013 Halloween flood in Austin that killed five people and damaged more than 500 homes in the Dove Springs and Onion Creek areas. Many of those affected homes lay outside a high-risk flood zone identified by the U.S. Army Corps of Engineers, but they were still within a 25-year flood plain, meaning there is a 4 percent chance they will flood each year. To attempt to mitigate the risk of future devastation, the Austin City Council authorized more than $90 million last year to buyout almost 475 properties in the flood plain area. Federal studies show that some of those homes should have never been built.

Bad development decisions have costs, but proactive responses to major flooding events have paid off for Austin and serve as a good model for San Marcos. After the 1981 Memorial Day flood that killed 13 people, the city of Austin spent $200 million to buy and raze 450 flood-prone homes along creeks, build flood walls and retention ponds, expand creeks for more water-carrying capacity, and improve storm drains in older neighborhoods. Those improvements have been credited with reducing the damage from floods over the past 30 years, especially in the central area of the city.

Still, Central Texas is always going to be prone to flash flooding because of its rocky soil, steep terrain and its location in the path of storms from the Gulf of Mexico and Pacific. As fast-growing cities like San Marcos continue to build, officials would be wise to be conservative with permitting development in the flood plain and invest in proactive flood control measures where development already exists.

San Marcos is among the 22,000 communities that participate in the voluntary National Flood Insurance Program, which requires jurisdictions to regulate flood-prone areas so that residents can get reduced-cost federal flood insurance. The program requires communities to prohibit construction in "floodways," which are certain to flood on a regular basis.

A San Marcos city ordinance requires buildings in the 100-year flood plain to be built 1 foot higher than the minimum level set by FEMA. Additionally, major projects are sometimes required to commission a flood-impact study.

However, despite participating in the federal program, San Marcos officials regularly approve development projects in the 100-year flood plain, which covers nearly a fifth of the city.

Complicating matters for San Marcos is the speed at which the area is growing. For the third consecutive year, the Census Bureau named San Marcos as the country's fastest-growing city in the country. More people in a flood-prone area can be a recipe for disaster if adequate development requirements aren't in place.

The U.S. Geological Survey suggests that development, or urbanization, increases the size and frequency of floods and exposes communities to increasing flood hazards.

"Development increases runoff. You can mitigate some of it, but cannot fully take away," Maidment said. "The more development we have, the more runoff there will be."

Of particular concern are the multifamily developments that have been built in the flood plain. The city does not require landlords to notify residents -- many of which are students -- that they live in a flood zone. The city notifies property owners of their statuses every year, but it's up to landlords to pass that information on the residents.

San Marcos city leaders should consider thorough flood control evaluation to help avoid "flood amnesia" that occurs as time goes by after a major disaster. Aiming for a much higher National Flood Insurance Program community rating would be a logical first step, as well as identifying cost-effective flood control and drainage projects. If nothing more, the city should seriously consider steering new development to less flood-prone areas until more adequate infrastructure exists to justify the risk of building in the flood plain.

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