Main Article Content
Two simple frequency decomposition techniques were used as part of a tidal response method to derive the hydraulic diffusivities of a freshwater-lens aquifer. Digital high-pass filtering can separate the tidal components of diurnal and shorter periods from longer-period components. Discrete Fourier transform can be used to isolate a specific tidal component. These techniques are easy to practice using the built-in functions of spreadsheet software. The applied techniques were each optimized for the frequencies of known major tidal components. Isolation of the specific tidal signals helps to reduce the errors of a basic tidal response method that uses in its calculations the amplitude attenuation and phase lag of a simple sinusoidal wave of groundwater fluctuations. Another advantage of the present tidal method is the utilization of two groundwater time series collected from near-shore and relatively inland sites affected by the same ocean tide. The method does not use surface-water observation, thus avoiding errors derived from generally possible surface-water/groundwater boundary effects.The tidal response method with simple decomposition techniques was used to investigate the aquifer properties of an uplifted limestone island located in a subtropical region of Japan. A freshwater lens is the principal water resource for this island and its sustainable development is desired. Significant hydraulic layering has not been reported in the limestone aquifer. Pairs of groundwater-level time-series data collected by simultaneous observations at near-shore and inland sites were analysed by the tidal response method. The results demonstrated heterogeneous aquifer diffusivity on the island, typically with larger values in the southeastern coastal part than in the northwestern coastal part, which is consistent with the planar distribution of the entire freshwater lens and the position of its maximum thickness that are slightly biased toward the northwestern side.
ALMEIDA, C. & SILVA, M.L (1983): Novas observações sobre o efeito de maré em aquíferos costeiros do Algarve [New observations of the tidal effect in coastal aquifers of Algarve – in Portuguese, with an English abstract].– Boletim da Sociedade Geológica Portugal, 24, 289–293.
AUSTIN, M.J., MASSELINK, G., MCCALL, R.T. & POATE, T.G. (2013): Groundwater dynamics in coastal gravel barriers backed by freshwater lagoons and the potential for saline intrusion: Two cases from the UK.– Journal of Marine Systems, 123–124, 19–32. doi: 10.1016/j.jmarsys.2013.04.004
BANERJEE, P., SARWADE, D. & SINGH, V.S. (2008): Characterization of an island aquifer from tidal response.– Environmental Geology, 55/4, 901–906. doi: 10.1007/s00254-007-1041-y
BARKEY, B.L. & BAILEY, R.T. (2017): Estimating the impact of drought on groundwater resources of the Marshall Islands.– Water, 9/1, 41. doi: 10.3390/w9010041
CAROL, E.S., KRUSE, E.E., POUSA, J.L. & ROIG, A.R. (2009): Determination of heterogeneities in the hydraulic properties of a phreatic aquifer from tidal level fluctuations: a case in Argentina.– Hydrogeology Journal, 17/7, 1727–1732. doi: 10.1007/s10040-009-0478-3
CARR, P.A. & VAN DER KAMP, G.S. (1969): Determining aquifer characteristics by the tidal method.– Water Resources Research, 5/5, 1023–1031. doi: 10.1029/WR005i005p01023
CHATTOPADHYAY, P.B., VEDANTI, N. & SINGH, V.S. (2015): A conceptual numerical model to simulate aquifer parameters.– Water Resources Management, 29/3, 771–784. doi: 10.1007/s11269-014-0841-6
CORBETT, D.R., DILLON, K. & BURNETT, W. (2000): Tracing groundwater flow on a barrier island in the north-east Gulf of Mexico.– Estuarine, Coastal and Shelf Science, 51/2, 227–242. doi: 10.1006/ecss.2000.0606
ERSKINE, A.D. (1991): The effect of tidal fluctuation on a coastal aquifer in the UK.– Ground Water, 29/4, 556–562. doi: 10.1111/j.1745-6584.1991.tb00547.x
FADILI, A., MEHDI, K., RISS, J., MALAURENT, P.H., BOUTAYEB, K. & GUESSIR, H. (2012): Oceanic tidal influence on the piezometric level variation of the coastal karst aquifer of Oualidia (Morocco) [in French, with an English abstract].– Africa Geoscience Review, 19/3, 135–150.
FERRIS, J.G. (1951): Cyclic fluctuations of water level as a basis for determining aquifer transmissibility.– International Association of Scientific Hydrology, Publication 33, 148–155.
GUO, M., WAN, J., JIANG, F. & HUANG, K. (2017): Estimating unconfined aquifer parameters based on groundwater tidal effect [in Chinese, with an English abstract] .– Earth Science, 42/1, 155–160. doi: 10.3799/dqkx.2017.012
HOUBEN, G. & POST, V.E.A. (2017): The first field-based descriptions of pumping induced saltwater intrusion and upconing.– Hydrogeology Journal, 25/1, 243–247. doi: 10.1007/s10040-016-1476-x
ISHIDA, S., TSUCHIHARA, T., YOSHIMOTO, S., MINAKAWA, H., MASUMOTO, T. & IMAIZUMI, M. (2011): Estimate of the amount of freshwater lens of Tarama Island, Japan [in Japanese, with an English abstract].– Irrigation, Drainage and Rural Engineering Journal, 273, 7–18.
ISHIDA, S., YOSHIMOTO, S., KODA, K., KOBAYASHI, T., SHIRAHATA, K. & TSUCHIHARA, T. (2015): Salt water intrusion into groundwater and problem on Vava’u Island and Lifuka Island, Kingdom of Tonga [in Japanese, with an English abstract].– Technical Report of the National Institute for Rural Engineering, 217, 1–12.
JHA, M.K., KAMII, Y. & CHIKAMORI, K. (2003): On the estimation of phreatic aquifer parameters by the tidal response technique.– Water Resources Management, 17/1, 69–88. doi: 10.1023/A:1023018107685
JO, S.-B., JEON, B.-C., PARK, E.-G., CHOI, K.-J., SONG, S.-H. & KIM, G.-P. (2014): Estimation of hydraulic characteristics and prediction of groundwater level in the eastern coastal aquifer of Jeju Island [in Korean, with an English abstract].– Journal of Environmental Science International, 23/4, 661–672. doi: 10.5322/JESI.2014.4.661
KOIZUMI, N., KITAGAWA, Y., KAZAHAYA, K. & TAKAHASHI, M. (1998): Volcanic gas concentration and aquifer permeability estimated from tidal fluctuations in groundwater level: Case of Koshimizu Well in Izu-Oshima, Japan.– Geophysical Research Letters, 25/12, 2237–2240. doi: 10.1029/98GL01409
KRIVIC, P. (1982): Transmission des ondes de marée à travers l’aquifère côtier de Kras [Transmission of tidal waves across the coastal aquifer of Kras – in French].– Geologija, 25/2, 309–325.
MARTIN, J.B., GULLEY, J. & SPELLMAN, P. (2012): Tidal pumping of water between Bahamian blue holes, aquifers, and the ocean.– Journal of Hydrology, 416–417, 28–38. doi: 10.1016/j.jhydrol.2011.11.033
NIETO LÓPEZ, J.M., ANDREO NAVARRO, B. & MUDARRA MARTÍNEZ, M. (2016): Hydrogeological parameters assessment by tidal influence analysis in the coastal aquifers of Bajo Guadalhorce (Malaga province, southern Spain) [in Spanish, with an English abstract].– Geogaceta, 59, 39–42.
OHZEKI, M., IMAI, R., TAKAYANAGI, H. & IRYU, Y. (2014): Stratigraphy and geologic age of the Ryukyu Group on Tarama-jima, Ryukyu Islands, Japan [in Japanese].– Abstracts of the 121st Annual Meeting of the Geological Society of Japan, R5-P-19.
OOGA, H., FURUKAWA, H. OGURA, I. & NISHIDA, T. (1974): Groundwater of Tarama Island, Okinawa Prefecture [in Japanese].– Abstracts of the 81st Annual Meeting of the Geological Society of Japan, 368.
PERRIQUET, M., LEONARDI, V., HENRY, T. & JOURDE, H. (2014): Saltwater wedge variation in a non-anthropogenic coastal karst aquifer influenced by a strong tidal range (Burren, Ireland).– Journal of Hydrology, 519B, 2350–2365. doi: 10.1016/j.jhydrol.2014.10.006
ROTZOLL, K., GINGERICH, S.B., JENSON, J.W. & EL-KADI, A.I. (2013): Estimating hydraulic properties from tidal attenuation in the Northern Guam Lens Aquifer, territory of Guam, USA.– Hydrogeology Journal, 21/3, 643–654. doi: 10.1007/s10040-012-0949-9
SHIRAHATA, K. (2010): Analysis of water balance in formation of freshwater lens through electric conductivity measurement [in Japanese].– Journal of the Japanese Society of Irrigation, Drainage and Rural Engineering, 78/6, 514–515.
SHIRAHATA, K. & NAGATA, J. (2009): A study of freshwater lens in Taramajima Island for a large-scale water resource development in the future [in Japanese].– Geotechnical Engineering Magazine, 57/9, 42.
SHIRAHATA, K., ISHIDA, S., YOSHIMOTO, S. & TSUCHIHARA, T. (2014): New simple method for estimating hydraulic properties of a freshwater-lens aquifer by analysis of tidal groundwater fluctuations [in Japanese, with an English summary].– Technical Report of the National Institute for Rural Engineering, 215, 141–154.
SHIRAHATA, K., YOSHIMOTO, S., TSUCHIHARA, T. & ISHIDA, S. (2016): Digital filters to eliminate or separate tidal components in groundwater observation timeseries data.– Japan Agricultural Research Quarterly: JARQ, 50/3, 241–252. doi: 10.6090/jarq.50.241
SHIRAHATA, K., YOSHIMOTO, S., TSUCHIHARA, T. & ISHIDA, S. (2017): Improvements in a simple harmonic analysis of groundwater time series based on error analysis on simulated data of specified lengths.– Paddy and Water Environment, 15/1, 19–36. doi: 10.1007/s10333-016-0525-3
TERRY, J.P. & CHUI, T.F.M. (2012): Evaluating the fate of freshwater lenses on atoll islands after eustatic sea-level rise and cyclone-driven inundation: A modelling approach.– Global and Planetary Change, 88–89, 76–84. doi: 10.1016/j.gloplacha.2012.03.008
TREFRY, M.G. & BEKELE, E. (2004): Structural characterization of an island aquifer via tidal methods.– Water Resources Research, 40/1, W01505. doi: 10.1029/2003WR002003
TREFRY, M.G. & JHONSTON, C.D. (1998): Pumping test analysis for a tidally forced aquifer.– Ground Water, 36/3, 427–433. doi: 10.1111/j.1745-6584.1998.tb02813.x
VACHER, H.L. (1978a): Hydrology of small oceanic islands-influence of atmospheric pressure on the water table.– Ground Water, 16/6, 417–423. doi: 10.1111/j.1745-6584.1978.tb03256.x
VACHER, H.L. (1978b): Hydrogeology of Bermuda—Significance of an across-the island variation in permeability.– Journal of Hydrology, 39/3–4, 207–226. doi: 10.1016/0022-1694(78)90001-X
YAMADA, S., YONAHARA, N. & SOBUE, H. (2009): The Quaternary coral reef complex deposits (Ryukyu Group) and hydrogeologic features on Tarama-jima, Okinawa Prefecture, Japan [in Japanese].– Abstracts of the 116th Annual Meeting of the Geological Society of Japan, 83.
YANG, H., SHIMADA, J., MATSUDA, H., KAGABU, M. & DONG, L. (2015): Evaluation of a freshwater lens configuration using a time series analysis of a groundwater level and an electric conductivity in Minami-daito Island, Okinawa Prefecture, Japan [in Japanese, with an English abstract].– Journal of Groundwater Hydrology, 57/2, 187–205. doi: 10.5917/jagh.57.187
YAZAKI, K. (1977): Geology of the Taramashima District [in Japanese, with an English abstract].– Geological Survey of Japan, Kawasaki, 28p.