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First in a series

Houston is sinking - and has been for decades.

As torrential rains have pounded the city in consecutive years, leading to repeated, heavy and deadly flooding, this inconvenient fact contributes to the region's misery.

Parts of Harris County have dropped between 10 and 12 feet since the 1920s, according to data from the U.S. Geological Survey.

State and local officials have made various efforts over the past 40 years to stabilize the ground, but some areas continue to sink - by as much as 2 inches per year.

Spring Branch, where Interstate 10 and Beltway 8 meet, has dropped 4 feet since 1975. Jersey Village, along Route 290 and to the west of Beltway 8, is almost 2 feet lower than it was in 1996. And Greater Greenspoint, where Interstate 45 intersects with Beltway 8, has given up about 2 feet in the last decade alone, according to USGS data.

"When you lose that much, it makes an area prone to floods when they weren't historically," said Mark Kasmarek, a hydrogeologist for more than 30 years with the USGS.

There is little mystery to why this is happening: The developing region draws an excessive amount of groundwater to keep itself quenched. Over the last century, aquifers here have lost between 300 and 400 feet, leaving the land to collapse.

The science behind this phenomenon is called subsidence.

Houston sits in one of the nation's largest subsidence bowls, so-called because of the crater effect that happens when the ground caves.

A USGS map of Harris County shows the city's bowl containing many smaller bowls, some with 8- to 9-foot drops in elevation. Many of these areas are in places known to flood, like the Heights, Montrose, downtown and near the East End.

Rainfall collects and pools in the bowls, instead of seeping through the land, Kasmarek said.

Residents have seen it up close in Meyerland, a 6,000-acre neighborhood in southwest Houston that lost about a foot and a half over a 13-year period in the 1980s and early 1990.

Cracked foundations, uneven sidewalks and shifted floorboards are often telltale signs of subsidence, residents said.

Shifts in elevation do more than alter topography, said John Blount, a Harris County engineer. They also ruin the efficiency of a city's drainage system.

Blount saw a recent example of this when he and a crew were repairing a section of Kirby Drive.

"We noticed that drainage lines weren't at the grade they should've been, and they weren't allowing water to drain as quickly as they should," he said. "It's because the ground wasn't at the same level anymore."

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Over the years, Texas lawmakers enacted bills to create subsidence or water conservation districts in counties that include Harris, Fort Bend, Montgomery and Galveston. The goal was to keep the region elevated by developing ways to reduce groundwater consumption.

The Harris-Galveston Subsidence District, created in 1975, was the first of these districts. Since its creation, subsidence rates have slowed greatly. Instead of losing a foot every 10 years, many areas saw that rate cut by a little more than two-thirds.

However, development has outpaced controls in other parts of the region, where groundwater continues to be pumped to meet demands.

Aquifer levels are declining in northwestern Harris County, Fort Bend County and Montgomery County, a preliminary report released this month by the Harris-Galveston Subsidence District concluded.

Long-term fixes - like drawing from surface water and creating new reservoirs - are still on paper.

Of the 50 major public water suppliers in Harris, Fort Bend and Montgomery counties required to submit audits to the state, at least 30 draw all of their water from the ground - delivering more than 14 billion gallons a year, according to the most recent data.

The other suppliers use a combination of ground and surface water.

Privately owned wells also draw from the aquifers.

"Telling homeowners they can't take free water from a well on their property is like telling Texans they can't drive a truck," Kasmarek said. "Many people close their eyes to it and don't believe in (subsidence)."

It's important to educate the public, he said, because once the damage is done, it can't be easily corrected. Even after switching to surface water, the ground will continue to sink for several years, Kasmarek said. It takes time for the aquifers to adjust.

"It doesn't happen overnight," he said.

The Harris-Galveston Subsidence District estimates that northwest Harris County will sink another 11/2 feet by 2030 even after surface water conversion takes place.

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To understand subsidence, think about what's beneath the ground - layers of sand, gravel and clay. Water flows through those layers.

But when the water is removed for drinking or agricultural use, the layers smash together and the ground sinks. It's a process that would occur naturally, Kasmarek said, but at a glacier's pace. Development exacerbates the collapse.

"Houston is one of the best examples in the U.S., but it's a national and global problem," he said.

Arizona, California and Louisiana have struggled with subsidence. Elevation drops, coastlines disappear and parts of cities flood that historically haven't.

India and Japan also have worked to fight subsidence by placing water restrictions on groundwater withdrawals.

Houston was the first place where subsidence was studied in the United States, according to Kasmarek.

Because of the region's relatively flat, featureless topography, the effects of subsidence were quickly noticed.

"Oil Bay" was one of the most extreme examples.

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Trevia Beverly remembers when the secluded peninsula protruding into Crystal Bay near Baytown - just east of Houston - was home to oil and gas industry executives who turned "Oil Bay" into a place for upscale, waterfront properties.

At the development's height, about 1,500 residents lived in what was known as Brownwood, according to USGS estimates.

This was in the 1950s, and Beverly was entering her 20s.

Beverly said her grandparents had lived there, and it was a wonderful place to raise a family and own a home.

Two decades later, however, residents noticed the bay creeping into their backyards. The water swallowed entire sections of the peninsula.

A routine rain would cause severe flooding.

"It was truly heartbreaking," she said. "A lot of people tried to warn us, but the land began to sink, and no one really knew what to do."

Hurricane Alicia struck what some called the deathblow in August 1983. A 101/2-foot storm surge damaged three-fourths of the homes.

The peninsula, which had dropped about the height of a standard basketball goal over 30 years, was soon abandoned.

"No one wanted to leave, but they had no choice," Beverly said.

Since then, regional leaders and scientists have shifted their focus inland, to not only protect Houston's underground resources but also to prevent a repeat of what happened in Brownwood.

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The key to stabilizing the land lies in how fast the subsidence districts can move more developments - old and new - to consume more of their water from surface supplies than the ground, said Mike Turco, director of the Harris-Galveston Subsidence District.

Some of that surface water will come from existing resources like Lake Conroe, the Brazos River and the Trinity River, but pipeline projects have been delayed multiple times with fluctuating timetables.

Montgomery County has begun using water from Lake Conroe and expects to keep drawing from there. The conversion wasn't cheap. Many county residents saw tax increases to finance the infrastructure and treatment plants needed for the $500 million project.

Beverly, who hasn't visited her old neighborhood since its abandonment, said the region's struggles appear similar to what happened to the Baytown subdivision, though on a much larger scale.

A few rocky, winding roads still lead into Brownwood.

Trees and weeds now sprout from abandoned foundations and concrete swimming pools. Trenches flowing with water carve the area into a marshy nature preserve run by the city.

A few streets from the old subdivision lead into the bay.

"The banks used to be so high, and that's what kept the water away," she said. Once the land began to sink, "nature just took it back."

If the city doesn't do more to address its floods, she said, "Houston will also end up regretting it one day."