The 1978 Houston-Galveston and Texas Gulf Coast Vertical Control Surveys
Comparisons between leveling surveys of different epochs are used to determine vertical displacement of permanent bench marks. Displacement of bench marks usually represents the movement of the surrounding area. In this report, the 1978 Houston-Galveston and Texas Gulf Coast releveling surveys are compared to the 1963, 1973, and 1976 releveling results. The changes in elevations of bench marks common to two or more epochs are tabulated and plotted in appendix A. From, these differences, contour maps were prepared for the 1963-78 and 1973-78 epochs in the 2 degrees x 2 degrees area of maximum subsidence. Annual subsidence rates computed for the 1973-78 period are about 25 percent less in the maximum subsidence area than the rates computed for the 1963-73 period.