Correcting Tidal Responses in Observed Water Well Levels During Coastal Aquifer Tests

Abstract

A modified tidal efficiency algorithm, ESTA, was developed to correct observed water well levels in tidally responsive coastal areas to get best estimates of aquifer properties and well production characteristics. The algorithm was developed during groundwater studies in Puerto Peñasco, northeastern Gulf of California, Sonora, Mexico. ESTA predicts standing water well levels in response to tides. ESTA requires initial sea and well calibration data, from which sea-well relationships are calculated. It needs tidal data for the time period when projected standing water well levels are desired. The method uses a single cosine or sine function for rising or falling tides, respectively. ESTA tended to overpredict water levels, especially on rising tides, on the average of about 0.05 ft, as shown in analyses at five coastal well sites completed in low to moderately permeable sand and coquina. ESTA can be improved by application of error analysis, but this will not be necessary in most cases, as errors are generally very small for most aquifers and tidal ranges. When ESTA was applied to an aquifer test in highly permeable coral near Kahuku, northehore Oahu, Hawaii, rising -tide water well levels were overpredicted and falling -tide water well levels were underpredicted by 0.10 and 0.33 ft, respectively. Error analysis reduced these errors to 0.06 and 0.16 ft.