Filtering methods in tidal-affected groundwater head measurements: Application of harmonic analysis and continuous wavelet transform. (November 2016)

• Record Type: Journal Article
• Authors: Sánchez-Úbeda, Juan Pedro; Calvache, María Luisa; Duque, Carlos; López-Chicano, Manuel
• Is Part Of: Advances in water resources. Volume 97(2016)
• Page Start: 52
• Page End: 72
• Publication Date: 2016-11
• Subjects: Tidal influence -- Filtering methods -- Groundwater head -- Coastal aquifer -- Harmonic analysis -- Wavelet transform; Hydrology -- Periodicals; Hydrodynamics -- Periodicals; Hydraulic engineering -- Periodicals; 551.48
• DOI: 10.1016/j.advwatres.2016.08.016
• Languages: English
• ISSNs: 0309-1708

Abstract

Highlights: A new methodology for filtering tidal influences in groundwater heads is proposed. Two oceanographic methods are adapted to filter induced tide on groundwater head data. The CWT methods have been proved more effective than HA for tidal influence studies. The length of the record used determines the accuracy of the tide fitting. The tidal constituents were better resolved at increasing depths in the aquifer. Abstract: A new methodology has been developed to obtain tidal-filtered time series of groundwater levels in coastal aquifers. Two methods used for oceanography processing and forecasting of sea level data were adapted for this purpose and compared: HA (Harmonic Analysis) and CWT (Continuous Wavelet Transform). The filtering process is generally comprised of two main steps: the detection and fitting of the major tide constituents through the decomposition of the original signal and the subsequent extraction of the complete tidal oscillations. The abilities of the optional HA and CWT methods to decompose and extract the tidal oscillations were assessed by applying them to the data from two piezometers at different depths close to the shoreline of a Mediterranean coastal aquifer (Motril-Salobreña, SE Spain). These methods were applied to three time series of different lengths (one month, one year, and 3.7 years of hourly data) to determine the range of detected frequencies. The different lengths of time series were also used to determine the fit accuracies of the tidal constituents for both the sea level and groundwater heads measurements. The detected tidal constituents were better resolved with increasing depth in the aquifer. The application of these methods yielded a detailed resolution of the tidal components, which enabled the extraction of the major tidal constituents of the sea level measurements from the groundwater heads (e.g., semi-diurnal, diurnal, fortnightly, monthly, semi-annual and annual). In the two wells studied, the CWT method was shown to be a more effective method than HA for extracting the tidal constituents of highest and lowest frequencies from groundwater head measurements.