The New York Times had a great article with maps which showed why the flooding was so bad in Houston. Here is the article:
As floodwaters from Hurricane Harvey recede in Houston, one thing that’s been revealed is that some of the damage — financial, physical, emotional — could have been avoided.
Flood hazard maps by the Federal Emergency Management Agency, showing the 100-year floodplain, an area with a 1 percent risk for flooding in any given year, mark where homeowners are required to have federally sponsored flood insurance. This is one of the few early warning signals the United States has for flooding. For Houston, those maps were thoroughly inadequate. Early assessments show many homes were flooded even though they were located far from the designated floodplains. Many homes in what’s known as the 500-year floodplain — with a 0.2 percent chance of flooding in a year — are also flooded.
Areas surrounding the Katy Prairies, sprawling grasslands in western Harris County, provide one such example. The region has been heavily developed over the past 30 years, sometimes overlapping or abutting floodplains. Local officials did not do enough to preserve native grasses, set aside open spaces or improve drainage.
100-YEAR FLOODPLAIN 500-YEAR FLOODPLAIN BUILDING DAMAGE
2016
BUILDING DAMAGE
FLOODPLAIN
Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery); FEMA (building damage, through Sept. 2, 2017)
Damage around Katy was not restricted to floodplains identified by FEMA.
“It gives people a feeling of complacency if they are not required to buy insurance,” said Howard Kunreuther, the co-director of the Wharton Risk Management and Decision Processes Center at the University of Pennsylvania. He would like to see FEMA provide people the “gradation of their risk.”
Less understandable is how often these flood maps were ignored in Houston, where policies encouraged development in flood-prone areas while reducing the region’s natural defenses to flooding.
And while the region has its own unique history, geography, economy and approach to growth, the lessons it will be learning in the coming weeks would apply to many other areas of the country.
FEMA flood risk zones
Building Damage
100-YEAR
500-YEAR
OUTSIDE FLOODPLAINS
INSIDE FLOODPLAINS
Spring
Hockley
HOUSTON
Jersey Village
1
Highlands
Katy
2
Pasadena
Baytown
East Houston
2
1
Damaged
inside
floodplains
Damaged buildings
outside floodplains
Source: FEMA (building damage); Beyond Floods (floodplains)
Houston’s Rampant Development
With Houston’s economy booming, thanks in large part to oil and gas industries, residential and business development spread. As developers carved out new neighborhoods, they sometimes overlapped or abutted the floodplain — zones highly susceptible to flooding. Elsewhere, roads, parking lots, homes and businesses covered over wetlands and prairies that absorb flood waters.
An area east of Katy was submerged in floodwaters after rainfall breached the Addicks Reservoir. One neighborhood, Westlake Forest, was built in what the FEMA designated a floodplain.
Westlake Forest
Neighborhood
Civilians patrol for residents in need of evacuation in the Westlake Forest neighborhood of Katy, Texas.
Alyssa Schukar for The New York Times
FLOODPLAIN
A newer development located on the south side of Kingwood, a community in northeast Houston, was constructed throughout the late 1990s and 2000s directly inside the floodplain. Satellite photos show the area overwhelmed by floodwaters after the storm.
Other regions, like Cypress in northwest Harris County, or Willow and the Woodlands on the northern side of Houston, also show heavy development throughout the late 1990s and 2000s. Both areas experienced heavy flooding during the hurricane.
Kingwood
MAJOR FLOODING
FLOODPLAIN
Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery)
Cypress
MAJOR FLOODING
FLOODPLAIN
Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery)
The Woodlands
MAJOR FLOODING
FLOODPLAIN
Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery)
FEMA maps are updated infrequently because Congress has not appropriated enough money for the work. The maps do not take into account the future impact of climate change or the impact of likely real estate development in the area. In addition, FEMA has not created flood maps for the entire country, leaving some home buyers unaware of flooding risks, said Larry Larson, a senior policy advisor at the Association of State Floodplain Managers.
A more nuanced view of flood risk may be possible. Data by Syndeste and Beyond Floods considers factors like previous flood damage and land cover as part of a risk assessment, showing many properties in downtown Houston not in the floodplain are still at significant risk.
FEMA flood risk zones
Flood outlook score per block
100-YEAR
500-YEAR
VERY HIGH
HIGH
MODERATE
LOW
VERY LOW
Near
Northside
Greater Heights
HOUSTON
Rice Military
Fourth Ward
Downtown
Hyde Park
Sources: FEMA (floodplains); Beyond Floods (flood outlook)
Damage for Many, Insurance for Few
Right now, more troubling is how ill-prepared even those in the current floodplain are to deal with Harvey’s aftermath. The vast majority of residents across the 30-county region struck hardest by hurricane Harvey also did not have insurance, according to Beyond Floods, a company that tracks and analyzes flood data.
HOUSTON
Columbus
VICTORIA
Beeville
Portland
SHARE OF UNINSURED HOMES
WITHIN HIGH-RISK FLOOD ZONES
0%
100%
Source: Beyond Floods
While federal flood insurance will help some whose homes have been ruined, only about 15 percent of homes in Harris County had policies under the flood insurance program, according to the Insurance Information Institute. Some choose not to buy policies because of the cost, and they are not eligible for subsidies.
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