Big Box Stores in Humble During Harvey

Mitigating Root Causes of Flood Damage

Part 3 of a 3-part series – In Part 1 and Part 2 of this series, I discussed root causes of flood damage. Today, let’s start a community brainstorming session about possible ways to address the issues. I’ll briefly summarize each of the root causes, then list three or four ideas to address them. What are your thoughts?

Unreliable Predictions of Future Rainfall

We can’t do anything about the amount of rain that falls from the sky. We can only control how we prepare for it. 

  • Where do we build homes? 
  • How high do we build them? 
  • How much drainage capacity should we build in new subdivisions? 
  • How much impervious cover should we allow? 
  • How much stormwater detention capacity will it take to protect people downstream? 

The amount of rainfall we predict forms the design basis for answers to all those questions and more. If you get the prediction wrong, you get the infrastructure wrong. Homes and businesses flood. 

But those predictions are a moving target. Research indicates the number and magnitude of extreme rainfall events is increasing worldwide. 

Compared to extreme rainfall estimates used through the 1990s, 100-year/24-hour estimates for Houston increased from 13 inches to 18 inches. 100-year events under the old system are now 25-year events

If you designed a ditch to hold 13 inches of rain and got 18, where would that extra 5 inches go? 

It would pond in streets, homes and businesses. The diagram below shows the difference.

Relative cross-sections of a ditch needed to accommodate a 100-year rainfall before and after Atlas 14.

Extreme rainfall probability estimates in this region have increased only twice since the 1960s. So there’s a lot of stormwater infrastructure around us built to old standards. It’s now under capacity. The problem is even worse in older parts of the city.

What can we do to improve reliability of our predictions and minimize this disconnect? 

  1. Update hydrologic design standards faster and more frequently. This would help minimize the amount of infrastructure designed to antiquated standards. Much of the existing hydrologic infrastructure in the US underperforms on reliability. (Note: The Floods Act of 2022 already calls for 10-year updates, but there’s no guarantee local authorities will adopt them.)
  2. Build larger safety margins into both estimates and regulations. Instead of building one or two feet above the 100-year floodplain, build even higher. 
  3. Incorporate a rate of increase for potential climate change. (Note: NOAA is already working on this.)

Conflicting Floodplain Standards and Building Codes

Rural areas around Houston often still use older design standards. Lower standards help attract development because they lower developers’ costs. And more development fuels growth and tax revenue. 

But it’s a dangerous bargain. Insufficient mitigation can flood people downstream. And as the region expands, insufficient mitigation will eventually cause even those recently developed areas to flood. 

So, how can we get the entire choir singing from the same songbook?

  1. Adopt a statewide or regional approach to development standards that affect flooding.
  2. Create a regional flood authority.
  3. Raise awareness of increased risk in/from areas with lower standards.

Building Too Close to Threats

People often build too close to flood risks, such as rivers. Developers love the cheap land and buyers love proximity to water. Until the floods come, it’s a “win-win” relationship propped up by the availability of nationally subsidized flood insurance. Then people realize they’ve been lulled into a false sense of security and they demand help. 

But there may be no room for mitigation. To widen channels or build stormwater detention basins, HCFCD must sometimes buy out whole neighborhoods. That raises costs, extends mitigation timelines, and often creates political conflict.

Possible solutions:

  1. Buy up green corridors along streams before areas develop. Use it for recreation to enhance community health and home values.
  2. Require greater setbacks from rivers, streams, channels and detention basins to create room for future expansion.
  3. Eliminate grandfathering clauses in floodplain regs that allow development in areas that we know will soon become floodways when new maps are released.
  4. Change Benefit/Cost Ratios so that the purchase of raw land next to streams qualifies for federal grants before development occurs. Buying undeveloped land costs less than buying developed. But it’s difficult to estimate the future benefit of conserving undeveloped land.

Upstream Changes that Undermine Downstream Assumptions

Upstream development should not create “adverse impacts” downstream. But it frequently does. It can increase the amount of runoff; increase sedimentation; and make flood peaks build faster, higher, more frequently. 

Suddenly, all those design assumptions for roads and developments downstream become invalid. 

What do we do?

  1. Protect green spaces next to rivers, streams and channels.
  2. Tax floodplain development at higher rates.
  3. Beef up enforcement to make sure developers don’t cut corners.
  4. Ensure everyone plays by same rules.

Difficulty of Adapting to Those Changes Downstream

Once an area builds out, it’s difficult to expand stormwater infrastructure. 

How can we retain flexibility for the future?

  1. Enforce “no adverse impacts” in upstream development
  2. Monitor construction to ensure it complies with approved plans
  3. Establish greater safety margins
  4. Plan for future expansion of infrastructure.

Historical Unwillingness to Fund Flood Mitigation at Meaningful Levels

As memories of major storms recede, so does the sense of urgency to prepare for the next ones. Historically, we have underfunded flood mitigation. Before Harvey, for instance, HCFCD’s budget averaged only $120 million per year

  1. Increase awareness of issues throughout the region; build consensus around solutions.
  2. Communicate value being created…consistently.
  3. Eliminate political interference in flood control; let professional engineers do their jobs.

Final Recommendations

Making such changes happen will take civic engagement by large numbers of people with a long view. It will also require putting public interest above self interest.

Politicians respond to voters. But they also respond to special interests. 

In the end, our leaders must balance competing interests. Reducing future flooding will take relentless incremental change on many fronts. Even when memories of the last disaster fade.

Invitation to Comment

What are your thoughts on ways to mitigate the root causes of flood damage? Please send to me via the contact page of this web site. Remember to indicate whether I can use your name or you need to remain anonymous. I’ll make sure our leaders see your ideas either way.

Posted by Bob Rehak on 11/22/23

2276 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.