6/4/24 – Rainfall in the upper part of the San Jacinto River (SJR) Basin during early May storms rivaled Hurricane Harvey totals there. And if you consider year-to-date rainfall (YTD) totals, the amount above normal equals two Harveys in places!

The comparisons with Harvey help put into perspective some extraordinary rainfall in a relatively small geographic area that affects a much larger area.

The comparisons help explain why many people in the Lake Houston Area felt the May flood was far out of proportion to the amount of rainfall received. The most extreme rains did not fall on downstream residents’ heads. For downstream residents, the rains fell unseen – 50 miles north.

Let’s look at data for Huntsville first. Even though the City itself technically sits just outside the San Jacinto River Basin, rainfall south and west of the City entered both the East and West Forks of the San Jacinto.

Harvey Week vs Week Around May Storm

During Hurricane Harvey week in 2017, the SJRA gage southwest of Huntsville received 20.46 inches of rain.

During the late April/early May storm of 2024, the same gage received just a little less – 18.4 inches.

This area got almost as much rain in one week this May as it did during Harvey. Now let’s look at year to date numbers.

Year-to-Date Totals Vs. Harvey

The National Weather Service maintains another gage in Huntsville which accounts for a slightly different total. But I’m using it for the YTD comparison because of the powerful graph. It illustrates how much rain the area recently received compared to normal. (We already know the Harvey total from the first bar graph above.)

From the brown line above, we can see that area normally gets 20 inches of rain through the end of May. This year it got 58.97 inches, almost triple the annual average at that point in the year.

The amount above normal (38.97 inches) is almost twice what the Huntsville area received during Harvey (20.46 inches)!

National Weather Service Data

So far this year, the upper river basin has received almost three Harveys worth of rain, or two above the normal YTD rainfall…for that latitude.

I should note here, that inland areas usually receive less rain than coastal areas during hurricanes. So if you’re saying, “Wait a minute! We received more than 20 inches of rain during Harvey,” you’re right. You also probably live south of Huntsville.

How to Compare Totals at Other Gages

Want to see what happened at a gage near you? HCFCD’s Flood Warning System lets you enter any date range using the historical feature. Just click on the “More Info” button associated with any gage. Or do it for the whole river basin to see the distribution of totals.

To quickly compare the distribution during Harvey, just change the dates to 8/25/17 and 8/29/17. It’s fun to explore. And it makes a fun learning experience for your kids. Teach them how to become “data detectives.” It could turn them into homeroom heroes.

Alternatively, you can compare Harris County gages during Harvey by consulting the tables at the end of HCFCD’s final Harvey report. It contains peak rainfall totals for all the gages above for time periods ranging from five minutes to four days.

The Reports Page of this website contains similar reports on other storms under the Major Storms tab.

Significance and Recommendations

There’s a point to all this data. We can draw several conclusions and recommendations from it:

• Extreme rainfall in the northern tier of the river basin contributed to the flooding that many experienced 50 miles south.
• Rainfall coming from the west and east was less intense and likely accounted for less damage downstream.
• Heavy rains can fall outside of hurricane season. In fact, spring storms can exceed hurricane rainfall totals and rival hurricane intensity.
• We need regional flood control. The people near Huntsville were not prepared for this event. Neither were people to the south protected.
• Hurricane Harvey wasn’t a once-in-a-1,000 year rainfall. Pretending it was will jeopardize public safety. We need better building codes and drainage regulations in areas that haven’t already been updated since Harvey.
• We also need updated flood maps that show current risk to help protect homebuyers. New floodplain surveys were conducted after Hurricane Harvey. But FEMA hasn’t yet released new risk maps based on those surveys. Many fast-growing areas in the region still base development decisions on data from the 1980s. That puts homebuyers at risk.

Flood Risk: A Shifting Target

Even as FEMA finalizes new flood-risk maps, understand that Mother Nature, sand mines, and insufficiently mitigated upstream developments are constantly changing the landscape through erosion and deposition.

The resulting blockages and reduction in conveyance may now contribute to increased flooding on smaller rains. Consider River Grove Park and the Kingwood Diversion Ditch. Both are now blocked by sand from upstream.

It’s not as bad as it was after Harvey…yet. But up to five feet of sand was deposited in this area during the recent flood. So give it a few more floods.

As the City of Houston readies a $34 million dollar dredging program (that doesn’t even include River Grove), look what’s coming downstream to us.

The West Fork snakes through 20 square miles of sand mines between US59 and I-45. And due to pit capture, the West Fork currently runs through a mile-long sand pit.

That raises one final recommendation: I wish the City could use its influence in Washington and Austin to have the EPA and TCEQ eliminate these blatant abuses.

In the meantime, the Kingwood Service Association will debate its own dredging program and the future of River Grove this Thursday night. To attend the online meeting, contact the KSA office at 281-358-5192 for a Zoom link.

Posted by Bob Rehak on June 4, 2024

2471 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.