Tag Archive for: relic channel

Living Landscape: San Jacinto River Before Lake Houston and Now

Geologic change happens so slowly, most people won’t live or stay long enough in one place to perceive it. Then something happens to make you crank up the Wayback Machine and look more closely. Yesterday was one of those days for me. The Army Corps announced that it was going to begin dredging part of the West Fork mouth bar area.

That raised the question, “Which part?” That wasn’t announced. So I asked Tim Garfield, retired chief geologist for one of the world’s largest oil companies, what he would do. He felt it was important to re-establish the river’s natural channel. So I asked him where it was. (Spoiler alert: It’s between the mouth bar and Atascocita Point.) But in the process of figuring this out, I learned many more things about the mouth bar and a river I take for granted. I’ll save those for the end.

70 Years of Change on the River

Garfield led me to the Perry-Castañeda Map Collection of Texas Topographic Maps at the UT Library Online. He found this map from 1949 of Moonshine Hill. It’s exactly 70 years old! The 1949 date means we can see where the river was before the dam and lake were built in 1955.

The San Jacinto in 1949 before Lake Houston was impounded in 1955. For a higher resolution version of this map, click here. This map shows what geologists call “the relict channel.”

Kingwood, Atascocita and Huffman Before Settlement

This map shows areas that would eventually become Atascocita, Kingwood, and Huffman. It includes the area where the mouth bar has formed between Kings Point and Atascocita Point.

You can tell a lot by looking at this map. You can tell even more when you superimpose it over a satellite view of the area today in Photoshop. Suddenly, you see how the landscape has changed. In fact, it changed so much that I had problems aligning the two images.

Map Superimposed Over Satellite Image At Varying Opacities

However, the county line and 1960 are still in the same location. So I used those as reference points. Then I varied the opacity in the top layer (the old map) so that you could see more and more of the current landscape. At different percentages, you can see how various features have changed over time.

Here’s what the sequence looks like starting with 1949 and today. I started by cropping tighter on the area of interest, the West Fork where the Corps is dredging. I include several different opacity ratios because some changes become more apparent at one ratio than another.

100% opacity for 1949 map.
0% 1949 and 100% today.
60% 1949 and 40% today.
50% 1949 and 50% today.
33% 1949 and 67% today.
25% 1949 and 75% today.

Most Visible Changes

Starting from the left:

  • In the 33/67 image, notice how the river once meandered near US59 and how much further south it was.
  • In the 50/50 image, notice how much of the Romerica land was swamp in 1949…and still is.
  • In the 75/25 image, notice how much the river migrated north just north of Kings River estates.
  • In the 25/75 image, notice how much area the lake claimed.
  • In the 33/67 image, notice how far north the river has shifted under the West Lake Houston Parkway bridge.
  • In the 33/67 image, notice how Atascocita Point has grown past the relict channel.
  • In the 60/40 image, notice how the mouth bar grew at the confluence of a relict stream bed within the lake and the relict channel of the West Fork. You can also see this pretty clearly in the 25/75 image.
  • In the 25/75 image, notice how the relict West Fork channel used to hug Atascocita Shores.

Key Map

This image shows locations referenced above for those who may not be familiar with them.

Key to locations

Do you see other things that I did not? Please let me know through the contact form on this web site.

As the dredging program moves forward, these maps may also help inform dredging strategy. Stay tuned.

Posted by Bob Rehak on 6/13/2019

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