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Thursday, August 28, 1997

Northwest Houston sinking faster than coastal areas

By TERRI LANGFORD / Associated Press Writer

HOUSTON -- Residents on Houston's northwest side are feeling a little low right now, but that sinking feeling has nothing to do with an emotional downswing.

New data shows northwest Houston is now the fastest sinking land in the coastal area. Between 1987 and 1995, some areas have dropped some 1.98 feet.

Houston's had a subsidence, or sinking problem, for years. But officials had been more concerned about the southeast side of Harris County and Galveston.

This new trend affecting the northwest side, revealed in a National Geodetic Survey, is important but not surprising, according to those who track sinking land for the Houston area.

"It's not new information," Ron Neighbors, general manager of the Harris-Galveston Coastal Subsidence District, said Wednesday.

But it does mean a fine-tuning of the agency's subsidence plan. The plan sets a timetable by which areas must convert from groundwater, which comes from underground sources, to surface water obtained from lakes or rivers.

And that worries some northwest-area residents, who say they can't convert to surface water under the existing timetable and aren't excited about seeing their water bills go up. Surface water costs more to deliver than groundwater.

"We're not convinced that there is a problem in North Harris to the extent the plan suggests," Floyd Mechler, president of the North Harris County Water Users Association, told the Houston Chronicle.

Taking the new information into account, Neighbors' agency has until next year to submit an updated plan to the state for the surface water conversion in northwest Harris County.

"Our plan needs to be adjusted every few years anyway," said Neighbors.

The existing plan calls for east Harris County to convert to using 80 percent surface water by 2005, central-north Harris County by 2002, west and northwest Harris by 2010 and the far northwest by 2020.

Houston's poor soil composition has made subsidence an ongoing problem. When underground water is pumped out, the layers collapse and the land essentially sinks. Topsoil, which helps protect the underlying layers, is stripped during hurricanes and torrential rains, compounding the situation.

"It's because of the geology that we have in this area. The ground underneath us is sands and clay and sands and clay," Neighbors said. "The clay, when you lower the water level, compact, and those many, many layers of clay, they sink."

When too much water was pumped from underground along coastal areas in the late 1960s and early 1970s, the land dropped about six inches a year. The Houston Ship Channel has sustained the most dramatic losses, more than nine feet in the 100-year period ending in 1987.

Houston, according to recent statistics, is about 49 feet above sea level.

Other areas in Texas that depend on underground aquifers for its water supply, like San Antonio, don't encounter the same subsidence when water is pumped from sources like the Edwards Aquifer.

"When they pump water, the water level just goes down and they don't have to deal with the area of subsidence," Neighbors said.

The creation of a manmade lake system outside Houston -- lakes Houston, Conroe and Livingston -- helped reduce subsidence in the southeast, along the Gulf of Mexico, to near zero.

"What we're interested in is the reduction of pumping," Neighbors says.

"We have made a lot of real good progress in controlling subsidence. Industry and cities have cooperated very, very well. And the public cooperated in paying higher water bills for surface water."

More than half of Houston has converted to surface water sources.