More People Live in Texas Floodplains than Live in 30 States

According to Texas Water Development Board data compiled for the first state flood plan, 5.9 million Texans live in 100- or 500-year floodplains. That means more people live in Texas floodplains than live in 30 states. Yep. Thirty entire states have populations smaller than that of Texas floodplains.

Other key observations also emerge from the data:

One in five Texans lives in a floodplain
42% of those live in the San Jacinto watershed.
The number of floodplain dwellers in the San Jacinto watershed alone exceeds the population of 15 states and the District of Columbia.

Where Biggest Problems Are

No other watershed comes close to 42%. To understand where the most people live with the most flood risk, see the table below. I compiled it from reports by the 15 regional flood planning groups in Texas.

*Column 3 shows people living in 100-year floodplain (1% annual chance) and Column 4 shows the 500-year (.2% annual chance) floodplain population.*

When looking at all people living in floodplains, Texas has almost 5.9 million. The last column shows where the largest concentrations of those people reside:

Only two other watersheds, the Trinity and Lower Rio Grande, reported double-digit percentages.
Trinity had 11.7%.
Lower Rio Grande had 17%.
No other watershed even made it over 5% of the floodplain dwellers.

The pie chart below really drives home the lopsided percentage of the state’s flood-plain dwellers living in the San Jacinto basin. San Jacinto is the large green area.

*Compiled from data reported by each of Texas’ Regional Flood Planning Groups.*

The San Jacinto basin has more people living in floodplains than the next five watersheds put together.

Possible Reasons for San Jacinto Issues

The TWDB report does not explain why. Likely, a number of factors contribute to the high percentage:

The state’s largest concentration of people, jobs, industry
Rapid growth and lax enforcement of development regulations
Insufficient upstream mitigation
Proximity to coast, tropical storms/hurricanes
High rainfall rates
Low, flat terrain

Floodplain Dwellers as Percent of State’s Total Population

The U.S. Census Bureau now estimates that 30,029,572 people live in Texas. With almost 5.9 million of them living in a 100- or 500-year floodplain, that means a whopping one in five live in floodplains.

Of the 20% of Texans who live in floodplains:

8% live in a 100-year (1% annual chance) floodplain
12% live in a 500-year (0.2% annual chance) floodplain.

So, statewide, more people prefer to live in the less risky floodplains. But that’s not the case in every watershed. See the San Antonio watershed in the table above. Three times more people live in the riskier, 100-year floodplain than the 500-year.

Coastline Concentrations

The numbers also show concentrations of floodplain dwellers near other parts of the Texas coastline.

The lower Rio Grande has 13 times more people living in a floodplain than the upper Rio Grande.
The lower Colorado has twice as many people living in a floodplain than the upper Colorado.
The lower Brazos has 2.5 times more people living in a floodplain than the upper Brazos.
The San Jacinto, which is one of the state’s shorter rivers and mostly near the coastline has the highest number of people in floodplains by far.

This 2014 NOAA study showed that 40% of the U.S. population lives in coastal counties. Density is far higher in coastal counties compared to inland areas. Coastal counties have 40% of the population but only 10% of the land.

Coastal areas also face different issues than inland communities. According to NOAA, “These include increased risks from high-tide flooding, hurricanes, sea level rise, erosion, and climate change.”

Cost of Making People Safe

The San Jacinto Regional Flood Planning Group recommended $46 billion worth of studies and mitigation projects in its regional plan. And the San Jacinto is just one of 15 watersheds in the state!

In sharp contrast to the magnitude of mitigation needs, the legislature voted only approximately $1 billion for flood prevention projects this year.

If I’ve learned one thing about flood prevention, it’s that nothing moves quickly.

Need for More Awareness

And that gives me a sinking feeling – especially knowing how few people have flood insurance and how many more need it.

The floodplains in our area are huge. We have a lot of people. And thus, the scary numbers for the San Jacinto watershed. And also consider this. The numbers above are likely understated, because they only reflect riverine flooding and not street flooding from poorly maintained ditches.

With few affordable structural solutions in sight, TWDB should spend some of their funds on public awareness and education while we wait for projects to happen. Few people understand how much flood risk they live with…until they flood.

For the entire 63-page report, see TWDB Board Agenda/Item #8 from their July 25th meeting. (Caution: 33 meg download.)

Posted by Bob Rehak on 7/29/23

2160 Days since Hurricane Har vey