Fort Bend County commissioners adopted its revised floodplain maps—a process the Federal Emergency Management Agency started nearly a decade ago. The revised maps are intended to provide reliable, up-to-date flood data using the latest mapping technology. They now represent the actual risk of flooding throughout the county, which means some property owners’ flood insurance rates are expected to increase.

Fort Bend County has a number of water channels that divert into the Brazos River and Oyster Creek. The water level in these channels can rise during heavy storms, and properties within the newly revised floodplains have a risk of being flooded.

FEMA’s updated flood maps are expected to assist developers, insurance agencies and management staff to make informed decisions regarding local development, County Judge Robert Hebert said.

“When the federal re-mapping started, Fort Bend County and the city of Sugar Land added $1.1 million to the FEMA budget for a [survey] of the Brazos River and Oyster Creek,” he said. “The improved accuracy of the baseline data, which resulted from this survey, greatly enhanced the accuracy of 100-year flood elevations throughout the county.”

Life in the floodplain

A floodplain is an area typically adjacent to natural rivers or streams that can see recurring flood events. They are categorized as a 100-year or 500-year floodplain. A 100-year floodplain has a 1 percent annual chance and a 26 percent chance of a significant flood in a 30-year period, and a 500-year floodplain represents a 0.2 percent annual chance and 6 percent chance of flooding in a 30-year period.

Although several areas around the county are protected by levees and were not affected by FEMA’s map revisions, dozens of property owners may now find themselves living in a floodplain. Flood insurance is required for properties inside the floodplain, and homes and businesses below the set base flood elevation are expected to see severe spikes in premium costs, according to data from FEMA.

“Using the new elevations, all of our levees were raised to minimize the threat to the lives and property they protect,” Hebert said. “While we all wished the previous elevations had survived unchanged or lowered, we can take comfort that the levees we have built and maintained for many years are truly protective, and we are confident that Fort Bend’s 100-year flood elevations are as accurate as modern technology and engineering can make them.”

With the adoption of the county’s updated flood maps, an estimated 200 Missouri City homes and businesses are within the floodplain—down from about 600 structures represented on FEMA’s former maps, assistant city engineer Jing Chen said. A number of homes in the Turtle Creek and Colony Lakes subdivisions were taken out of the floodplain with corrected mapping.

“For most homes in those areas, [resident’s] flood insurance premiums decrease as they are officially removed from the floodplain,” Chen said.

Revisions and appeals

FEMA’s process to redraw its national floodplains began as part of the agency’s plans to digitize existing flood maps, said Mark Vogler, general manager and chief engineer of the Fort Bend County Drainage District.

“They were just going to take our existing floodplain maps and convert them to digital,” he said.

When measuring the levels of the Brazos River, however, engineers with FEMA and the county came across a few discrepancies. There were three major flood events in the area throughout the 1990s, and water levels were about three feet higher than they should have been, Vogler said.

The county provided more than $1 million to further study the river at specific points and to perform a hydrology study.

“This was to determine how much water would come down river in a 100-year event depending on how high or low the river would be,” Vogler said. “We created the models and performed this analysis and came up with what we thought would be an accurate representation of a 100-year flood event in Fort Bend County. We have never seen that exact event, and we probably never will.”

When FEMA presented the floodplain maps to county officials, there were additional issues that needed to be addressed.

“We saw some things that we had commented on, but they were not addressed right,” Vogler said. “Now, the maps have become official, and we are going to have to go back as a county and do some map revisions, which will cost the county.”

This process, known as a Letter of Map Revision, will address concerns that were not addressed during the 90-day appeals process. Specifically, the county would like to revisit flooding potential in and around Quail Valley in Missouri City, Vogler said.

“We are looking to bring in a liaison to go to each community to help make the right decisions and know what the next steps are moving forward,” he said.

Download a full version of our guide to FEMA’s recently adopted flood maps here.

By John Rigg