On the determination of the compressible soil properties required to model subsidence in the area of Houston, Texas

One of the most important characteristics used to simulate the consolidation of an aquifer being pumped is the compressibility of the subsurface material. The present work, based on water level fluctuations and borehole extensometer data in the Houston area, determines, analyzes and compares the storage coefficient for either the elastic and inelastic ranges and the vertical hydraulic conductivity. Specifically coastal and inland areas are examined and values are recommended for use in modeling. In the coastal Houston area, data from Baytown, Clear Lake and the Johnson Space Center (NASA) taken each 28 days by the USGS since 1973 is analyzed. Similarly in the inland area, data from gages in the Southwest and Addicks areas are analyzed. The boreholes used for the extensometers at the Clear Lake, and Addicks sites were drilled to the base of the Evangeline aquifer. This is the deepest aquifer being pumped in most of the region. Since little or no water level decline has occurred below the aquifer, these extensometers measure total man-made consolidation (compaction). The extensometer at the Johnson Space Center is designed to measure compaction in the Chicot aquifer. This is the shallowest aquifer in the region; it overlies the Evangeline aquifer. The Clear Lake site was selected so that the information obtained there could be coupled with information from the Johnson Space Center. The results of the present analysis will be used to determine the percentage of subsidence for each of the aquifers being pumped in the region.