Whew! Luck and Aggressive Action Avert Major Flooding

Good to have the Pearl Harbor Day flooding in the rear-view mirror. And good that the worst predictions did not come true. So what happened? Did we just get lucky? Or did something go right for a change? It might have been a little of both.

Here’s what I know at 8 p.m. on Saturday night, about when the flood was expected to crest and flood multiple neighborhoods.

Lake Conroe Releases Have Peaked

According to Jace Houston, General Manager of the SJRA, releases from the Lake Conroe dam have likely peaked. The current release rate of 8181 cfs falls far short of previous floods and short of 9,000 to 11,000 cfs release rates predicted earlier.

Less Rain than Expected

That’s because we got less rainfall than predicted. Most of the area, including Lake Houston and upstream from Lake Conroe, received about 4.5 inches or less instead of the 8 to 10 predicted earlier.  And rain was fairly spread out over time. The heaviest rainfall seems to have happened in The Woodlands with some gages approaching 6 inches.

Aggressive Pre-Release by City

Finally, the City of Houston started releasing water from the Lake Houston Dam two days in advance of the storm. They took the lake level down two feet before the storm and kept releasing water during the storm. Had it not been for that, homes along the shoreline would almost certainly have flooded.

Looking across the flood-swollen San Jacinto at the US Army Corps of Engineers’ Command Site. Had the City not pre-released more than 2 feet of water from Lake Houston, this site would have been inundated.

Trending Steady or Down

At this moment, every stream gage that the SJRA reports upstream from the Lake Houston area is trending down. The peak has passed.

Harris County Flood Control shows that the gages at US59, West Lake Houston Parkway and FM1960 also appear to have peaked.

A photographic tour of the Kingwood area this afternoon showed that the river came out of its banks at River Grove Park and US59 and was on the verge of coming out in many other places. Surprisingly, I saw no flooded homes, not even on Marina Drive in Forest Cove. However, I did hear of many affected by street flooding, especially upstream in Montgomery County.

Still Much Mitigation Work to Do

Ben’s Branch by the Enclave and Kingwood Library had standing water. That should be a reminder that the County needs to make cleaning out this stream a high priority. 

One final point. Late this afternoon, I noticed a huge difference between the gages upstream and downstream from the dredging.

At 59, the West Fork exceeded its banks and peaked at 52 feet.
At West Lake Houston Parkway, the river was well within its banks and peaking around 45 feet.
At FM1960 the river was still well within banks and peaking at 44 feet.

Normally, these gages all read the same elevation. One can partially attribute the differences to spreading of the river. However one must also consider the huge blockages in the river that the Corps has not yet removed. At the moment, one of the biggest is just downstream from River Grove Park. Another, the mouth bar, blocks the river between Kings Point and Atascocita Point.

Even during a flood, the mouth bar (in the middle of this picture) stands out of the water by several feet and blocks the mouth of the West Fork. Water must make its way past this blockage through narrow passages on either side of it. It backs water up throughout the Humble/Kingwood area.
Here’s what the mouth bar looks like from the air, right after Harvey, before grass started growing on it. The area around it averages 1-3 feet deep. The deepest parts of the narrow channel reach 5 feet deep.

The Lake Houston Area lucked out this time due to aggressive action by City officials, a conservative release rate by the SJRA and the kindness of Mother Nature. I hope we don’t press our luck and assume that these blockages make no difference. They do. We need to remove them.

Posted by Bob Rehak on 12/8/2018

466 Days since Hurricane Harvey