How "Stacking Effect" Erodes Margins of Safety

4/13/26 – Since Hurricane Harvey in 2017, I’ve documented how numerous factors contribute to flooding. Individually, none is unique. You see them in operation everywhere around the world. But collectively, their impacts can “stack” in a way that degrades margins of safety and resilience – in some areas more than others.

San Jacinto West Fork at 59 during Harvey. — *US59 Bridge over San Jacinto West Fork during Hurricane Harvey, where numerous flood factors converged.*

Progressively Eroding Margins of Safety

Driving a vehicle makes a good analogy. A lonely highway. Rain-slick pavement. The dead of night. Bald tires. Too much speed. A tight curve. And a tired driver loses control.

In respect to flooding, the Lake Houston Area has:

Rapid upstream urbanization
Extensive floodplain development
Industrial-scale sand mining accelerating sedimentation
Low-gradient hydraulics
Constrained reservoir outflow
Fragmented governance

Now, Add 30-40% More Rain than Expected

A killer hurricane. Stalls over the Houston Area. The highest rainfall totals in the history of North America. Drainage channels clogged with sediment. A dam that can’t let water out fast enough. Homes built too close to water. Power gone. Communication out. Evacuation routes under water. And millions of people trying to flee. Simultaneously.

It’s not Hollywood; it’s Harvey.

Safety … Within Reason

We like to think of OUR safety as an “absolute.” Government and science will protect us, right? Wrong!

How much risk are we willing to live with? Said another way, “How much can we afford?” Engineers could design drainage systems that protect us from 100,000-year storms. But could we afford them? Probably not.

So, we look at probabilities and we compromise. We design systems to handle more than we expect. And they work great. Until the unexpected happens. Then we pray that everything doesn’t go wrong all at once. That our backup systems work.

And when they don’t, we’re left with that stale bag of potato chips in the back of the cupboard, rotting wallboard, and the kindness of strangers.

Systems Optimized for Competing Interests

We optimize communities to serve many different interests. Not just ours. And not just flood resilience. For instance, homes must be affordable, not just flood-safe. So, builders lobby for regulations that reduce their costs. And that may mean putting homes on smaller lots closer together, which…

Increases the percentage of impervious cover in a development
Speeds up runoff
Creates faster, higher flood peaks

And of course, to make new streets, you need sand for the concrete. So, fast-growing areas set up systems that let miners extract sand from floodways where it’s plentiful and pure.

But of course, that’s only a problem for people who live downstream. Until someone else does the same thing farther upstream.

Results: A Balancing Act

Here in the Lake Houston Area, we have a system where runoff is increasing, conveyance is decreasing, and control is fragmented—all at the same time. This combination is rare and particularly unstable.

But of course, it’s not all bad. Good people fight every day to keep you safe.

We have:

Harris County Flood Control District, widening and maintaining ditches, building stormwater detention basins, and maintaining thousands of miles of channels
Houston Mayor John Whitmire, Council Member Fred Flickinger, Houston Public Works Department and Coastal Water Authority, working to add more gates to the Lake Houston Dam
State Rep/ Charles Cunningham, who started a Lake Houston Area Dredging and Maintenance District to constantly remove accumulated sediment
State Rep. Dennis Paul, working to create a river-basin-wide flood control district
Thousands of first responders, honing rescue skills for the day they hope will never come
Armies of engineers, working to design drainage systems to keep you safe
Public servants like Harris County’s meteorologist Jeff Lindner, monitoring weather and maintaining flood warning systems 24/7/365 to warn you of severe weather
The Texas Water Development Board and its regional flood-planning groups
Representatives like Dan Crenshaw, who brought home hundreds of millions of dollars from Washington for flood-mitigation projects
Groups, like the Bayou Land Conservancy, Nature Conservancy and Coastal Prairie Conservancy working to preserve nature in ways that buffer us from flooding
Great people at FEMA, HUD, the GLO, and Texas Department of Emergency Management, ready to help when disaster strikes and all else fails.

It’s all a balancing act.

To prepare for the next flood, we must learn from the last – and act as if our lives depended on it.
Bob Rehak

For More Information

To learn more about how we can protect margins of safety, see the Lessons Page of this website.

Posted by Bob Rehak on 4/13/2026

3149 Days since Hurricane Harvey