Tag Archive for: flood frequency

Is Flood Frequency Really Increasing?

By Debbie Z. Harwell, PhD, Editor of Houston History Magazine

Many claims have been made about increasing local flood frequency. They raise the question, “How accurate are those statements?” The report “Significant Houston Area Floods” by Jill F. Hasling, CCM, offers an interesting list for analysis that ranges from April 1837 through February 2019 (two more floods have since occurred in May and September 2019). 

Increase in Flood Frequency

Our first flood took place in April 1837, just eight months after Houston was founded at the confluence of Buffalo and White Oak Bayous. Six months later another flood found Main Street under four feet of water. But Houstonians persisted…and so did the flooding.

In the first 100 years following Houston’s founding, it experienced 36 floods, in the next 82 years, it has seen an additional 146 floods, or four times as many as in the first century.

Broken down into 30-year periods, the trend looks like this. Note that only 3 years exist in the last column so far and it already has more floods than each of the first two 30-year periods.

Note: Last column contains only three years and already has more floods than each of the first two thirty-year periods.

Percentage of Tropical Vs. Non-Tropical Floods

One might think that our location along the Gulf Coast and the tropical systems that come ashore are to blame for this phenomenon, but tropical systems account for only 15% (27) of these events. The other 85% (155) were caused by rain that either fell in large quantities in a short period of time or lingered in the area for multiple days; this includes 22 winter storms.

Early Flood Mitigation Efforts

With the exception of the 1900 Storm, which hit Galveston but also caused fatalities and flooding on the mainland, the worst of Houston’s early floods occurred in 1929 and 1935 (watch video), causing multiple deaths and wiping out homes, businesses, bridges, and the main water plant. With two back to back floods of this magnitude it was time to take action.

In the midst of the New Deal, the federal government put the Army Corps of Engineers in the flood control business. Houston benefited with funding for the Barker and Addicks Reservoirs, completed in 1946 and 1948 respectively, after a delay during World War II. Although creation of two proposed drainage channels north and south of Buffalo Bayou to relieve flooding did not come to fruition, the reservoirs brought some relief along Buffalo Bayou.  

Influence of Urban Growth on Flooding

As Houston grew, so did it’s flooding problem, going beyond Buffalo and White Oak Bayous to include the other 22 Harris County watersheds. By 1983, Houston floods regularly saw the number of inundated homes reach into the thousands. In 1994, ninety subdivisions, including 3,400 homes, flooded. This flood was considered the benchmark for many Kingwood residents to determine the probability that their home might flood in the future. As a result, many did not have flood insurance when Harvey hit because they believed they were safe since their home did not have water in 1994. 

Today some people point fingers at others, saying their flooding problem is of their own making because they built or bought a house in the floodplain, when in fact the area where their homes are located did not have a flooding problem years earlier. Rather, development around them or upstream created issues. (View Kinder Institute’s interactive map of Houston development.)

This has been documented in Meyerland in the last four years, and the most recent floods in Kingwood’s Elm Grove in May and September 2019 also make a  similar case. The Elm Grove homes had never flooded and did not flood in Harvey, but now they have flooded twice in four months with the water levels increasing. Although a definitive cause for the May flood is in litigation, homeowners believe development north of them created the flooding problem. Sadly some of these residents also did not have flood insurance because they figured they were safe after Harvey.

How Quickly We Forget!

Increasingly, these rain events leave our infrastructure overtaxed, whether trying to handle street runoff or rising water in our bayous, streams, and rivers. It seems, though, that many people have let flooding fall off their radar if they were not personally impacted or time has passed, putting flooding out of sight, out of mind.

When the Kinder Institute asked Houstonians in its annual survey what they thought was the “biggest problem in Houston” prior to Harvey but after the Memorial Day 2015 and Tax Day 2016 floods, only 1% spontaneously replied “flooding.” That number grew to 15% in 2018 when asked post-Harvey. But when surveyed in 2019, with only street flooding the year before, the number who identified flooding as our biggest problem dropped down to 7%. Traffic was the leader, going from 24% in 2017 to 36% in 2019. 

The list of Houston area floods clearly shows that Houston has experienced more frequent flooding of an increasingly serious nature. Everyone thought Tropical Storm Allison was “off the charts” until Harvey hit. Imelda was not as bad as Harvey, but in just two short days it managed to be the seventh leading rain event in the nation.

Need for New Ways to Address Flooding

Major floods in four of the last five years demonstrate that the old ways of addressing flooding a little at a time, or doing nothing at all, are not adequate to protect our families, homes, and businesses and maintain our quality of life in Houston.

  • Debbie Z. Harwell, Ph.D.
  • Editor, Houston History
  • Instructional Assistant Faculty
  • University of Houston

Posted on 10/28/2019 by Debbie Z. Harwell, PhD with help from Bob Rehak

790 Days since Hurricane Harvey and 39 since Imelda


Drone Video Underscores Dangers of Development without Remediation

Yesterday, the area where a developer proposes a new high-rise development flooded for the fifth time this year. This underscores the need for remediation before any permitting.

It wasn’t an especially heavy rain last week. Kingwood received about 2.5 inches. Areas upstream averaged 3 to 4 inches. Yet the West Fork came out of its banks and flooded River Grove Park for the fifth time this year (February 26, March 28/29, July 4, December 7/8, December 27). The USGS Gage at US59 showed that the flood crested at about midnight. The crest reached almost 50 feet at US59.

The West Fork at US 59 crested at almost 50 feet from the most recent rains. In the days preceding, SJRA released 5-7,000 cfs from Lake Conroe.

Jim Zura of Zura Productions took his drone to River Grove during the last light before the overnight crest. The video shows that although the road was still useable, many of the park’s popular amenities were not. The playground, soccer fields, boat ramp and boardwalk all flooded.

Earlier this year, the US Army Corps of Engineers found that excessive sedimentation in the river contributed to excessive flooding. The frequency of these floods supports that conclusion. The Corps began dredging in late September to remove sediment, but has completed only about 20% of the project so far. Downstream blockages remain. And the biggest – at the mouth of the West Fork – is not even within the scope of the current dredging project.

The end of Zura’s video shows the soccer fields and adjoining property, including a small lake in the floodway. This flood gives us a glimpse of how a minor rain would affect the proposed high-rise development there.

Watch all the way to the end!

The frequency of these floods underscores the need to consider the implications of permitting such a major development – especially when officials know the engineering is based on obsolete data and flood maps that in no way reflect current realities.

Until remediation efforts are complete, officials should postpone consideration of the permit. Remediation efforts include:

  • Dredging the West Fork all the way from US59 to Lake Houston
  • Creating additional upstream detention
  • Adding flood gates to Lake Houston
  • Restoring the conveyance of local drainage ditches and streams.

Rainfalls of the magnitude that caused these five floods should happen about once every 2 years according to Harris County Flood Control. This year they happened five times: 10X greater than expected. A review of peak crest data since 1929 roughly confirms these expectations. In the 80 year since then, the river crested over 50 feet only 40 times.

A review of the same data shows that the river has crested over 57 feet 9 times in the last 80 years and six times since 1994.

I believe excessive sedimentation played a role in this frequency increase. Instead of flooding every other year like this, we’re flooding almost every other month. That’s significant enough to put the brakes on development in the floodway, at least until we understand the extent of the problems and can fix them.

These are my opinions on matters of public policy. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statutes of the Great State of Texas.

Posted by Bob Rehak on December 31, 2018

489 Days since Hurricane Harvey