Three months after Hurricane Harvey churned through Texas, dumping 51 inches of rain and damaging an estimated 150,000 homes, the state’s most populous county took a bureaucratic step that has huge implications for how it will deal with the risk of future flooding.
On December 5, Harris County, which surrounds the City of Houston, approved an overhaul of its flood rules, expanding them from 100-year floodplains—which have a 1 percent change of flooding in a given year—to 500-year floodplains. The new rules (which don’t apply inside Houston city limits) will compel people building houses in some areas to elevate them up to eight feet higher than before.
“We had 30,000 houses that flooded” from Harvey, said John Blount, the county engineer, who put forward the rule changes. Before the floodwaters even subsided, hundreds of county employees fanned out to survey the damage. “We went to every one of those houses and figured out how much water got in them, and then we did a statistical analysis,” Blount said.
The data was geocoded, factoring in location and neighborhood conditions, and one result was the increased elevation rule. (The county is also buying out 200 of the most vulnerable homes and hopes to buy out thousands more, but those represent a small fraction of the homes inside the floodplain.)
Harris County’s new rules are the most stringent flood-related development restrictions anywhere in the United States, according to Blount. If a future Harvey-sized deluge comes, almost all the homes in the area will be safe, he said: “Had that same event happened, at the same location but [with houses] built to the new standard, 95 percent or more would not have flooded.”
For a structure, standing water is a fearsome enemy. Even a small amount of flooding in a home can exile its inhabitants for weeks and require costly repairs. After Harvey, tens of thousands of evacuees lived in hotels or with friends as workers in their homes tore out drywall to prevent the spread of mold, which can sicken residents. And more Harveys are coming: As my colleague Robinson Meyer reported, a new MIT study concludes that Harvey-scale flooding in Texas is six times as likely now as it was in the late 20th century, and will only get more likely as this century wears on. More