May 2024 flood inundation map

How May 2024 Flood Compared to Harvey

Harris County Flood Control District (HCFCD) briefed the County’s Community Resilience Flood Task Force on how the extent of the May 2024 flood compared to Hurricane Harvey. In places, inundation matched Harvey. And in others it came close or fell short.

See the inundation map below. In my opinion, it dramatizes three things:

  • Serious flooding can happen any month of the year in the Houston region.
  • Flooding can happen anywhere that rain falls.
  • Flood-mitigation measures make a huge difference.
Inundation map from HCFCD comparing Harvey with May 2024 floods and evacuation zones.


As the map above shows, major rain can fall outside of a hurricane season. In fact, May is usually the third wettest month of the year in Houston, exceeded only by June and October.

Of seven major storms to strike this area since 2016, four have happened outside of hurricane season.


The worst rainfall in the early May floods happened at the very top of the San Jacinto river basin in the upper portions of the East and West Forks. Parts of those watersheds received almost 20 inches of rain.

In Huntsville, Harvey dumped only 2 more inches of rain than a training band of thunderstorms in May 2024. The map above shows the results.

Cypress, Spring and Lake Creeks, which originate on the west side, received roughly a quarter to a third of the rain that fell to the north during early May.

Rainfall totals for 8 days before May 6, 2024. Compare 18.4 at top of map to smaller totals farther south. From Harris County Flood Warning System.

However, during Harvey, the rainfall distribution was the opposite of the map above. Huntsville received about 17 inches while areas to the south received more than 40.

Flood-Mitigation Measures

The inundation map above shows the importance of another location-related variable: upstream stormwater detention. Note how much more blue you see on the West Fork than on the East Fork which is predominantly green. The West Fork has a dam at Lake Conroe which partially blocked the heaviest flows. The East Fork has no dams.

But the East Fork and Luce Bayou do have the sprawling Colony Ridge Development. And Colony Ridge, especially the first 12,000 acres, has only a minuscule amount of stormwater detention. The development is now 50% larger than Manhattan.

Development usually increases the speed and volume of runoff. Developers normally use detention basins to limit post-development runoff to pre-development rates, so that they don’t increase flooding.

But for the most part, that didn’t happen in Colony Ridge. And that contributed to flooding downstream.

The inundation map above should be a wakeup call. Of 16 major flood-mitigation projects identified in the San Jacinto River Basin Master Drainage Study, not one has even gotten to the drawing boards, much less off them – after four years.

Posted by Bob Rehak on 7/3/24

2500 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.