Use of Harmonic Analysis To Study Tidal Fluctuations in Aquifers near the Sea

Abstract

Sixteen days of water level records were collected from a tidal gage and from four wells situated in a line perpendicular to the shore at Borden, Prince Edward Island. These two sets of records are separated by harmonic analysis into three tidal components. In a confined aquifer, groundwater flow obeys linear potential theory so that each component represents a distinct test on the aquifer, which is analyzed for hydraulic conductivity and specific storage. The use of a line of wells permits the determination of the effective distance and an accurate determination of true tidal efficiency by two different plots. The values of hydraulic conductivity determined this way agree very closely with the values determined by packer tests on nearby wells. These results permitted examination of the composite wave and the single well technique. The unseparated composite wave was analyzed by using the maxima and minima from four days of records and by assuming a periodicity of 745 minutes. The calculated values of aquifer parameters differed very little from those determined by the individual components. In addition, each well was analyzed individually and the results were compared with those determined from the line of wells. The individual analyses can produce large errors because they do not permit an accurate determination of the effective distance.