Houston Lake dam failure analysis
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It has not failed yet, however, it is almost certain to exceed design limit.
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The dam has a giant spillway over 3000 feet long. The spillway is designed to release water from Lake Houston after it reaches 41 feet high.
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This is an update to my analysis after level of the lake rose from 51 ft to 52.38 ft.
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This means right now the dam is one big waterfall 3000 feet long and 11 feet thick.
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It is a good dam.
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The spillway was designed for a huge flow. It is made from reinforced concrete. It is highly unlikely that the 3000 foot long section will fail.
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However, dams have limits.
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No one expected rain like Houston has been having now.
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Engineers never expected the level of Lake Houston to exceed 54 feet.
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Right now we are less than 2 ft from design limit.
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The dam won't fail exactly at 54 feet. Engineers always build in a safety factor.
Provided the dam has been well maintained it should hold fine.
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This said, the rest of the walls of the dam are only 60 feet high. This means if the lake rises to 60 feet it will spill over walls not intended to act as a spillway.
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Again, the big long 3000 foot section is fine since it is designed to spill water.
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If the whole dam is overwhelmed, failure should be expected. It all depends on how high and for how long.
If there is a failure, obviously the flow of the San Jacinto will increase.
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My best guess is flow will go from about 600,000 cfs to 900,000 cfs.
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BTW The average flow of the Mississippi is right around 600,000 cfs and the peak measured flow was several million cfs.
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It is not as if there isn't already a flood. The fact is, the flood is happening whether the dam fails or not.
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Many people only talk about the rain event of 1994.
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The lake level peaked at 52.79 ft. That was pretty close to the design limit of 54 ft.
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If a non-hurricane rain event almost overwhelmed the dam in 1994, wouldn't that have been a big wakeup call? Apparently not. Houston continued building, continued damaging wet lands and made the situation worse.
No one seems to have considered it important to modify the dam so it would safely spill more water.
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Certainly at this point we have to accept that the current rain event will cause the lake level to go higher, and the maximum design limit will be exceeded.
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I have been tracking three river guages for rivers going into Lake Houston. One is now maxed out and can't read any higher. They just never dreamed to put the guage higher than 20 feet above the riverbanks. This means right now the East Fork of the San Jacinto has spilled over it's banks 20 feet deep in all directions.
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The West Fork of the San Jacinto is now reading over 67 feet and close to reaching maximum reading too. This means the flow in this channel going to Lake Houston is already more than the rain event of 1994.
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One thing people might think is the dam is supposed to help with flood control. This particular dam doesn't.
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The reason is capacity. The total volume of Lake Houston is about 5 billion ft3.
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That may sound big, however, you must consider how big the figure is for total volume coming into the lake per second. It's 100s of thousands of ft3/sec.
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Even if authorities emptied Lake Houston just before Harvey struck, the Lake would have been full again in a few hours.
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There is big spillway and two gates to release water from Lake Houston. Using an estimated 10 ft/sec flow rate I found the spillway and gates should be able to release 600,000 cfs before the dam is over topped.
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Will the flows reach 600,000 cfm?
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Maybe, it depends largely on how much rain falls in the next 48 hours. Reports are between 10-20 inches. Not good.
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Do I believe the dam will over top and fail. Well, let me put it this way. If I were below this dam I would be very interested to monitor current level.
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Here is a link:
https://waterdatafortexas.org/reserv...vidual/houston
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There were two rain events which exceeded 1994. However, both occurred before Lake Houston dam was built. One event was 1929 and the other 1940.
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An analysis I found performed based on the 1929 event estimated that the flow in the San Jacinto peaked at 600,000 cfs.
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It is perhaps not coincidental this is the number I determined to be absolute maximum spillway capacity. The engineers who designed the dam must have looked back to that 1929 flood.
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So what will happen?
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I can't say for sure. However, I think the possibility of a dam breach is real.
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Again this should not, if it occurs, be a major breach, and it is not as if there currently isn't an active flood already.
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This said keep an eye Houston Lake level. That dam may prove to be the most important lesson we learn the hard way.
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When you build in a flood area, build high and expect the water to come.
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