A 1949 map of the area now called Kingwood reveals that the homes in Elm Grove that flooded on May 7 were built in something once called the Odom Lake Swamp. It turns out, “Nature never forgets.”

I previously posted about this map in the context of how the West Fork has shifted over time. At the end of the post, I asked readers to write me if they found anything else interesting. One did. And it was a very interesting indeed.

He pointed to the area circled in red above. When I superimposed that over the present-day image below, my jaw dropped.

It’s True. Nature Never Forgets

The area labelled Odom Lake Swamp matches very closely the outline of the May 7 flood in Elm Grove that damaged almost 200 homes.

At a Houston Geological Society seminar on flooding that I attended last year, I remember several speakers talking about this phenomenon, including former Harris County Judge Ed Emmett. During heavy rainfalls, water gravitates toward its original channels.

One expert, who talked to me on condition of anonymity because of the lawsuits swirling around this issue, explained it this way. “Where old channels, swamps, meanders, etc. were filled in, during major floods, water always seeks the lowest point. Even if you fill in an area, it usually is still the lowest point of a larger area (or watershed) and during large rain storms, the water finds its way there.”

Current Flood Map Echoes 1949 Map

He attributed the Elm Grove flooding to a combination of clear cutting without mitigation upstream, heavy rainfall, and lower elevation. In fact, FEMA’s National Flood Hazard Layer Viewer shows that this part of Elm Grove is in the 100-year (aqua) and 500-year flood plains.

Implications

I’m not a lawyer and I don’t give legal advice, but it seems to me that this finding does little to change the legal lay of the land (no pun intended).

The residents south and east of Woodridge Village, despite being lower than surrounding areas, had never flooded before – even in Harvey.

They didn’t flood until the developer clearcut 268 acres, filled in natural streams, eliminated wetlands that act like natural detention ponds, and graded the property toward the area that flooded. All without constructing detention ponds until AFTER people flooded.

Had those ponds been in place, they should have held 13 inches of rain (a 100-year) rainfall. We didn’t get that much. The gage at US59 recorded 6.24 inches on May 7 over six hours. The heaviest rain fell during the noon hour when we got 3.64 inches.

Harris County meteorologist Jeff Lindner characterized the May 7th event as somewhere between a two and 50-year rain. Experiment with the different possibilities on the chart below.

Ten Lessons of May 7th

So aside from the Odom Lake Swamp being a historical curiosity, what can readers learn from this.

1. Flooding doesn’t always come from the river. Streets can flood homes when the rainfall rate exceeds the capacity of storm drains.
2. Before you buy a home, check historical maps. Learn whether the developer filled in lakes, ponds, swamps, or wetlands and then built your home on top of them. Remember: Nature never forgets!
3. If the answer is yes, question how much you want the property. Use the knowledge to negotiate a discount with which you can purchase flood insurance. That’s the best way to discourage unsafe development practices.
4. If you live downstream of an undeveloped area, be aware that floodplains are a shifting target. Just because you’re NOT in a floodplain today is no guarantee that you won’t be tomorrow. Upstream development can cause downstream flooding. So watch carefully.
5. Pay no attention to anyone who says, “Oh, that area will never be developed.” The more worthless the land, the bigger the profit potential.
6. If you live in this area, get flood insurance.
7. If you buy a low-lying home, be prepared to have your life disrupted.
8. Buyer beware.
9. Pressure your elected representatives to turn areas such as Woodridge Village into park land. When it was wetlands, it protected the people downstream from flooding and provided recreation.
10. Buying the property north of Elm Grove could have cost less than the damage to one home. (See appraisal below). Not buying the property was a costly decision.

Posted by Bob Rehak on 6/19/2019

659 Days since Hurricane Harvey