11/21/24 – Last week, the Harris-Galveston Subsidence District published a request for qualifications (RFQ) for consultants interested in conducting an alternative water supply feasibility study for Northeast Harris County.

Mike Turco, the District’s general manager, said he is specifically focused on the area east of Lake Houston, which is experiencing tremendous growth. The completion of the Grand Parkway has triggered much of that growth. And with it will come increased water demand, which has the potential to trigger subsidence.

“Alternative Water” Reduces Effects of Subsidence

The District defines “an alternative water supply” as a source that does not trigger subsidence. That most often means a source other than groundwater. Subsidence frequently results from excessive groundwater extraction. That can cause compaction of the earth and a whole range of consequences.

Such compaction caused an entire Baytown subdivision to sink into Galveston Bay.

Subsidence can also cause bowls in the landscape that trap water and increase flood risk Subsidence can even change the gradient of streams, slowing water down and backing it up.

An SMU study found that subsidence can cause faulting and damage structures such as homes, roads, pipelines, storm sewers, sanitary sewers and more.

Differential subsidence can create another set of problems altogether. For instance, the rate of subsidence at the Harris/Montgomery county line is much greater than the rate at the Lake Houston Dam.

That has the potential to tilt the lake toward its headwaters. And that could reduce the freeboard factor (feet above flood level) for homes in northern Harris County.

But alternative water sources can reduce all those impacts.

Examples of Alternative Water

In this region, surface water, i.e., from Lake Houston, is the most common “alternative water source,” according to the District’s definition. Lake Houston provides water for more than 2 million people without causing any subsidence.

So if we already have the major source of water in the area, why look at other alternatives? The planning horizon for water projects is typically 50 years. The RFQ specifically mentions recommendations to meet demand through 2070.

Given expected population growth during that period, the region may need more than Lake Houston. So it behooves us to look at all available alternatives.

According to Turco, right now, the City is already aggressively expanding water distribution from Lake Houston to areas like Spring, which has experienced some of the worst subsidence in the region – 30.5 centimeters, slightly more than a foot since 2007. See below.

The City is also expanding the Northeast Waster Purification Plant and bringing in water from Lake Livingston via the Luce Bayou Inter-basin Transfer Project. But will it be enough to meet demand 50 years from now?

Other alternative sources could conceivably reduce demands on Lake Houston. They include but are not limited to:

• Building a new reservoir
• Constructing pipelines from existing reservoirs
• Using reclaimed water for specific needs, such as irrigation or agriculture
• Desalination of Bay water

For More Information

A District spokesperson said they want to look at all options, costs and timing. To review the RFQ, click here.

For the District’s latest annual report on subsidence, see this six-page executive summary, this 47-page presentation, or the 307-page full report with appendices.

Subsidence is widely considered to be irreversible. It’s comforting to know that people are already planning for the welfare of our grandchildren.

Posted by Bob Rehak on 11/21/24

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