Lake Houston Gates Update

05/25/24 – Houston City Council members Fred Flickinger and Twila Carter met yesterday at the gates of Lake Houston with members of the Coastal Water Authority (CWA), Black & Veatch Engineering and Houston Public Works. They reviewed the status of repairs to a broken gate and a program to add 11 new gates to the dam.

Broken gate stuck in low position and not high position

During the flooding in early May 2024, news of a broken valve on Lake Houston Dam spread quickly on social media. Concerns about flooding fueled the rumors. Some people have heard that the gate is stuck closed. Others heard it was open. A visit to the doors yesterday confirmed it was stuck in the down position.

A CWA employee said one of the two chains used to raise and lower the gate had broken. This raised the possibility that the gate would become stuck sideways in its frame if they tried to lift it with the remaining chain attached only to one side. If the door became stuck, CWA would not be able to lower it again.

This meant that the lake would continue to lose water after the flood subsided. So they chose to leave it closed during the flood.

Lake Houston Dam also has a 3,160-foot-wide spillway in addition to the four gates.

Repairs will begin next week

The Coastal Water Authority (CWA) plans to repair the broken gate chain next week when the lake’s water level is lower. CWA manages Lake Houston for the city.

The repair team will include divers who will reattach the broken chain on the upstream side of the gate underwater.

The operation was too dangerous to attempt during the flood because other doors were open. And at the height of the flood, the water flowing through the 3,160-foot-wide spillway reached a height of six feet.

The divers could easily have been swept away by the strong currents. A cubic foot of fresh water weighs about 62 pounds. And at the height of the flood, more than 100,000 cubic feet per second flowed over the spillway and through the dam gates. That’s a lot of strength!

Current Lake Houston gates have limited capacity

Lake Houston’s current gates have a combined discharge capacity of only 10,000 cubic feet per second (CFS), or about 2,500 CFS each.

They are useful in pre-release scenarios, that is, releasing water before a storm to create additional storage capacity in the lake for stormwater. This can reduce flood peaks upstream and downstream of the dam.

However, Lake Houston’s current gates are so small that it may take several days to significantly lower the lake level. And during this time, the storms may move away. Meteorologists simply cannot provide precise estimates of where a storm will hit that far in advance.

Status of new larger doors

Adding more and larger gates to the dam could reduce the time it takes to lower the lake. And it would give dam operators more confidence that they’re not wasting water.

To release water more quickly, before and during a storm, the city of Houston plans to add 11 additional gates from Lake Houston to the land portion of the dam just east of the old gates.

The new gates could release a total of 80,000 CFS, bringing the total pre-launch capacity to 90,000 CFS, 9 times higher than the current rate.

The additional stormwater storage capacity in the lake could then help reduce flood peaks upstream and downstream.

The additional gates to Lake Houston could also release water more quickly during a storm.

According to the CWA, studies show the additional floodgates would not worsen flooding downstream. Homes have already been bought in the downstream areas that would be affected.

The City is currently in the design phase of the new gate structure. Construction is expected to begin sometime in 2025, according to council member Flickinger.

However, new doors should be custom made. No one offers gates of this size as commercially available items. Thus, lack of personnel in the supply chain could delay the delivery of the doors. It appears that companies that manufacture gates are still affected by staff shortages that began during the Covid pandemic.

Multiple Benefits of More Lake Houston Gates

When completed, the 90,000 CFS release capacity from the 15 Lake Houston gates (4 old, 11 new) would exceed the SJRA’s largest release ever from Lake Conroe – 79,000 CFS during Hurricane Harvey.

This would help improve the joint operations of the two lakes during floods.

But engineers at yesterday’s meeting warned the new doors are no silver bullet.

They say early release will not be necessary during small floods. And pre-release will have minimal impact during giant floods, like Harvey.

Indeed, large events like Harvey can replace the entire lake volume dozens of times over the course of the event. During such floods, lowering the lake a foot or two in advance will provide negligible benefit. Another monstrous flood could replace this volume in minutes.

However, the doors will provide significant improvements in 25, 50 and 75 year floods. This will provide a greater margin of safety for many people who have already been flooded or were about to be flooded during such events.

Posted by Bob Rehak on 05/25/24

2461 days since Hurricane Harvey