OPTIMAL IDENTIFICATION OF ELASTICALLY STORED WATER IN AN AREA OF PREVIOUS LAND SUBSIDENCE

Previous extraction of ground water from the Chicot aquifer in the Houston area, Texas, resulted in as much as 3 meters of land subsidence. Cessation of extractions from part of the area in the mid 1970s resulted in as much as a 60-meter rise in ground-water levels. This rise suggests that the aquifer now has elastically stored water that could be extracted without causing additional land subsidence. This renewable source of water may be valuable in augmenting other municipal water supplies. A constrained optimization model was used with a ground-water flow model to identify the maximum quantity of ground water that could be extracted. Constraints included keeping hydraulic head in the Chicot aquifer above the preconsolidation head, the lowest previous ground-water level. Optimal results indicate that 36,000 cubic meters per day (6,600 gpm) can be produced from 5 well sites for 10 years. Our technique involved the use of response functions, linear programming, and commonly used spreadsheet software.