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. 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.
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. 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.