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Hydrogeology Journal

, Volume 18, Issue 3, pp 749–759 | Cite as

Responses of atoll freshwater lenses to storm-surge overwash in the Northern Cook Islands

  • James P. TerryEmail author
  • Anthony C. FalklandEmail author
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Abstract

A category 5 tropical cyclone swept a storm surge across remote Pukapuka Atoll in the Northern Cook Islands (South Pacific Ocean) in late February 2005. Groundwater salinity (specific conductance) observations are reported for the 2-year post-storm period, with the aim of investigating the effects of saltwater intrusion on thin freshwater lenses within the atoll islets. This is the first article to present field observations of such an event. Specific conductance at shallow depths increased dramatically from potable conditions (approximately 1,000 μS/cm) to brackish levels unsuitable for drinking (up to 10,000 μS/cm) shortly after the cyclone. Subsequently, the freshwater lenses required 11 months to recover. Within the thickest aquifer, a well-defined saline plume formed at 6 m depth, sandwiching a freshwater layer beneath it and the base of the lens. Plume dispersal proceeded only gradually, owing to its formation at the start of the SW Pacific regional dry season and the low tidal range on Pukapuka. Consequently, the remnant of the plume was still present 26 months after the saltwater incursion. An important finding was that the freshwater horizon preserved at depth maintained salinity levels below 1,800 μS/cm (i.e. within usable limits) for at least 5 months after surface overwash.

Keywords

South Pacific Island hydrology Salt-water/fresh-water relations Overwash Freshwater lens 

Réponse des lentilles d’eau douce à une lame de submersion cyclonique dans les Iles Cook septentrionales

Résumé

Un cyclone tropical d’intensité 5 a provoqué fin février 2005 une vague submergeant le lointain atoll Pukapuka, au Nord des Iles Cook (Océan Pacifique Sud). Des observations sur la salinité de la nappe (conductivité spécifique) ont été enregistrées durant les deux années qui ont suivi l’épisode cyclonique, dans le but de comprendre l’effet de l’intrusion d’eau salée sur les minces lentilles d’eau douce des îlots à l’intérieur de l’atoll. Cet article est le premier à présenter des observations de terrain sur un tel évènement. Peu après le cyclone, la conductivité spécifique de l’eau à faible profondeur a augmenté de façon dramatique, d’un niveau potable (approximativement 1,000 μS/cm ) à des niveaux saumâtres (jusqu’à 10,000 μS/cm ) impropres à la consommation. Par la suite, il a fallu 11 mois pour que les lentilles d’eau douce se reconstituent intégralement. A l’intérieur de l’aquifère le plus épais, un panache bien délimité d’eau saline localisé à 6 m de profondeur a pris en sandwich un niveau d’eau douce limité par la base de la lentille. La dispersion du panache ne s’est effectuée que progressivement, en raison de sa formation en début de saison sèche du Pacifique SW et de la faible amplitude des marées à Pukapuka. Par suite, le reste du panache était encore présent 26 mois après l’incursion saline. Une découverte importante fut que le niveau d’eau douce préservé en profondeur a conservé des niveaux de salinité inférieurs à 1,800 μS/cm (i.e. dans des limites d’utilisation) pendant au moins cinq mois après la lame de submersion.

Respuestas de las lentes de agua dulce de un atolón sobrelavado de una onda de tormenta en las Northern Cook Islands

Resumen

Un ciclón tropical de categoría 5 provocó un onda de tormenta a través del atolón remoto de Pukapuka en el Norte de las Northern Cook Islands (Océano Pacífico Sur) en febrero de 2005. Se reportan las observaciones de salinidad del agua subterránea (conductividad específica) correspondientes a un período de 2 años posteriores a la tormenta, con el objeto de investigar los efectos de la intrusión de agua salada en las delgadas lentes de agua dulce dentro de las isletas del atolón. Este es el primer artículo que presenta observaciones de campo de tal evento. La conductividad específica en las profundidades someras se incrementó dramáticamente desde las condiciones de potabilidad (aproximadamente 1,000 μS/cm) a niveles de agua salobre inaptos para beber (hasta 10,000 μS/cm) poco tiempo después del ciclón. Subsecuentemente, las lentes de agua dulce requirieron 11 meses para recuperarse por completo. Dentro del acuífero de mayor espesor una bien definida pluma salina se formó a 6 m de profundidad, aprisionando una capa de agua dulce debajo de ella y la base de la lente. La dispersión de la pluma se produjo solo gradualmente, debido a su formación en el comienzo de la estación seca de la región del SO del Pacífico y la baja amplitud de marea en Pukapuka. Consecuentemente, el remanente de la pluma estuvo aún presente 26 meses después de la intrusión de agua salada. Un hallazgo importante fue que el horizonte de agua dulce preservó su profundidad manteniendo niveles de salinidad por debajo 1,800 μS/cm (es decir dentro de los límites para el uso) por lo menos 5 meses después del sobrelavado superficial.

北库克群岛环礁淡水透镜体对风暴潮越浪的响应

摘要

2005年2月末, 5级龙卷风所致风暴潮侵袭北库克群岛 (南太平洋) Pukapuka环礁。此后两年间对地下水的盐度 (比电导) 进行了监测, 以研究咸水入侵对环礁小岛薄层淡水透镜体的影响。本文是研究此种事件的首篇文章。龙卷风过后, 浅部饮用水 (约1,000 μS/cm) 变为不适合引用的咸水 (达10,000 μS/cm) , 比电导增加显著。11个月后, 淡水透镜体方完全恢复。最厚的含水层中, 地下6m深度出现一个被很好刻画了的咸水晕, 夹在其下的淡水层和透镜体底部之间。由于其形成于西南太平洋地区旱季开始和Pukapuka低潮差之时, 晕的扩散是逐渐发生的。结果, 晕的残余在咸水入侵26个月之后依然存在。一个重要的发现是, 深部盐度低于1,800 μS/cm (在可利用限值内) 淡水带在越浪发生之后至少保留了5个月。

Respostas das lentes de água doce em atóis a submersões provocadas por marés ciclónicas nas Ilhas Cook do Norte

Resumo

Em fins de Fevereiro de 2005, um ciclone tropical de Categoria 5 gerou uma maré ciclónica que atravessou o remoto Atol de Pukapuka, nas Ilhas Cook do Norte (Pacífico Sul). No período de dois anos posterior à tempestade registaram-se as observações de salinidade da água subterrânea (condutância específica), com o objectivo de investigar os efeitos da intrusão salina nas delgadas lentes de água doce do interior dos ilhéus. Este é o primeiro artigo a apresentar observações de campo deste tipo de evento. A condutância específica a pequenas profundidades aumentou fortemente desde condições de potabilidade (aproximadamente 1,000 μS/cm) até níveis salobros impróprios para consumo (até 10,000 μS/cm) pouco tempo depois do ciclone. Subsequentemente, as lentes de água subterrânea precisaram de 11 meses para recuperar completamente. No seio do aquífero mais espesso formou-se uma pluma salina bem definida, à profundidade de 6 m, ensanduichando uma camada de água doce entre a sua base e a base da lente. A dispersão da pluma prosseguiu muito gradualmente, dado que se formou no início da estação seca regional do Pacífico SW e numa altura de baixa amplitude das marés em Pukapuka. Consequentemente, os resquícios da pluma estavam ainda presentes 26 meses depois da invasão salina. Uma descoberta importante é que o horizonte de água doce preservado em profundidade manteve níveis de salinidade abaixo de 1,800 μS/cm (i.e. dentro de limites de consumo) até pelo menos cinco meses depois da submersão da superfície.

Notes

Acknowledgements

The authors wish to acknowledge the efforts of the Pukapuka Island Secretary and the staff of the Pukapuka Island Administration for obtaining the groundwater data during the period of monitoring. Mrs Li Kheng Lee, cartographer at the Geography Dept. of the National University of Singapore is thanked for drafting Figs. 1 and 5. Dr Kolja Rotzoll and another anonymous reviewer provided constructive suggestions that enabled many improvements to the original version of the manuscript.

References

  1. Anderson WP Jr (2002) Aquifer salinization from storm overwash. J Coast Res 18:413–420Google Scholar
  2. Anderson WP Jr, Lauer RM (2008) The role of overwash in the evolution of mixing zone morphology within barrier islands. Hydrogeol J. doi: 10.1007/s10040-008-0340z Google Scholar
  3. Anthony SS (1991) Case study 7: Majuro Atoll. In: Falkland A (ed) Hydrology and water resources of small islands: a practical guide. UNESCO, Paris, pp 368–374Google Scholar
  4. Bailey RT, Jenson JW, Olsen AE (2009) Numerical modeling of atoll island hydrogeology. Ground Water 47:184–196CrossRefGoogle Scholar
  5. Burns WCG (2002) Pacific Island developing country water resources and climate change. In: Gleick PH, Burns WCG, Chalecki EL, Cohen M (eds) The world's water 2002–2003: the biennial report on freshwater resources. Island, Washington, DC, pp 113–131Google Scholar
  6. Carlson DA, Van Biersel TP, Riley Milner L (2008) Storm-damaged saline-contaminated boreholes as a means of aquifer contamination. Ground Water 46:69–79Google Scholar
  7. Chu P-S (2004) ENSO and tropical cyclone activity. In: Murnane RJ, Liu K-B (eds) Hurricanes and typhoons: past, present and future. Columbia University Press, New York, pp 297–332Google Scholar
  8. Clarke S (2005) Tropical Cyclone Percy (TD-10F/TC-20P) 24 February–5 March. http://www.australiasevereweather.com/cyclones/2005/summ0502.htm. Cited September 2008
  9. Depledge D (1999) Water. In: Rapaport M (ed) The Pacific Islands: environment and society, 1st edn. Bess, Honolulu, HI, pp 66–73Google Scholar
  10. de Scally FA (2008) Historical tropical cyclone activity and impacts in the Cook Islands. Pac Sci 62:443–459CrossRefGoogle Scholar
  11. Dharmagunawardhane HA, Vithanage M (2008) Status of a tsunami affected coastal aquifer along the east coast of Sri Lanka. In: Bhattacharya P, Ramanathan AL, Mukherjee AB, Bundschuh J, Chandrasekharam D, Keshari AK (eds) Groundwater for sustainable development: problems, perspectives and challenges. Taylor and Francis, London, pp 223–231Google Scholar
  12. Diaz Arenas A, Falkland A (1991) Characteristics of small islands. In: Falkland A (ed) Hydrology and water resources of small islands: a practical guide. UNESCO, Paris, pp 1–9Google Scholar
  13. Dillon P (1997) Groundwater pollution by sanitation on tropical islands. Technical documents in hydrology no. 6, IHP-V. UNESCO, Paris, 31 ppGoogle Scholar
  14. Elsner JB, Kossin JP, Jagger TH (2008) The increasing intensity of the strongest tropical cyclones. Nature 455:92–95CrossRefGoogle Scholar
  15. Falkland AC (1994) Climate, hydrology and water resources of the Cocos (Keeling) Islands. Atoll Res Bull 400:52Google Scholar
  16. Falkland A (2005) Pukapuka, Cook Islands, report on water investigations, February 2004–February 2005. Report No. EHYD 2005/46, prepared on behalf of GHD Pty Ltd for the Australian International Development Assistance Agency and the Cook Islands Government, March 2005, Ecowise Environmental, Canberra, AustraliaGoogle Scholar
  17. Falkland AC, Brunel JP (1993) Review of hydrology and water resources of the humid tropical islands. In: Bonell M, Hufschmidt MM, Gladwell JS (eds) Hydrology and water management in the humid tropics. International Hydrology Series, Cambridge University Press, Cambridge, pp 135–163Google Scholar
  18. Falkland A, Woodroffe CD (1997) Geology and hydrogeology of Tarawa and Christmas Island, Kiribati. In: Vacher HL, Quinn TM (eds) Geology and hydrogeology of carbonate islands. Developments in sedimentology, vol 54. Elsevier, Amsterdam, pp 577–610Google Scholar
  19. George R, Weaver D, Terry J (1996) Environmental water quality: a guide to sampling and measurement. Department of Agriculture, Gov. of Western Australia, Perth, 38 ppGoogle Scholar
  20. Gray SC, Hein JR, Hausmann R, Radtke U (1992) Geochronology and subsurface stratigraphy of Pukapuka and Rakahanga atolls, Cook Islands: late Quaternary reef growth and sea-level history. Palaeogeogr Palaeoclim Palaeoecol 91:377–394CrossRefGoogle Scholar
  21. Hamlin SN, Anthony SS (1987) Groundwater resources of the Laura area, Majuro Atoll, Marshall Islands. US Geol Surv Water Resour Invest Rep. 87-4047, 69 ppGoogle Scholar
  22. Hastings PA (1990) Southern oscillation influences on tropical cyclone activity in the Australian/south-west Pacific region. Int J Climatol 10:291–298CrossRefGoogle Scholar
  23. Hein JR, Gray SC, Richmond BR (1997) Geology and hydrogeology of the Cook Islands. In: Vacher HL, Quinn TM (eds) Geology and hydrogeology of carbonate islands. Developments in sedimentology, vol 54, Elsevier, Amsterdam, pp 503–535Google Scholar
  24. Hunt CD (1997) Hydrogeology of Diego Garcia. In: Vacher HL, Quinn TM (eds) Geology and hydrogeology of carbonate islands. Developments in sedimentology, vol 54, Elsevier, Amsterdam, pp 909–931Google Scholar
  25. NIWA (2005) The island climate update, No. 56. May 2005. National Institute for Water and Atmospheric Research, Wellington, New Zealand, 6 ppGoogle Scholar
  26. NOAA (2008) Tidal station location and ranges. National Oceanic and Atmospheric Administration, Washington, DC. http://co-ops.nos.noaa.gov/tides06/tab2wc3.html. Cited October 2008
  27. Oberdorfer JA, Hogan PJ, Buddemeier RW (1990) Atoll island hydrogeology: flow and freshwater occurrence in a tidally dominated system. J Hydrol 120:327–340CrossRefGoogle Scholar
  28. OCHA (United Nations Office for the Coordination of Humanitarian Affairs) (2005) Cook Islands and Tokelau: tropical Cyclone Percy, OCHA situation report No. 5, OCHA, New York. http://www.reliefweb.int/rw/RWB.NSF/db900SID/SNAO-6B2KVA?OpenDocument. Cited September 2006
  29. RSMC-Nadi (2005) Tropical cyclone summary 2004–2005 season. Regional Specialized Meteorological Centre Nadi–Tropical Cyclone Centre. Fiji Meteorological Service, Nadi, Fiji, 14 ppGoogle Scholar
  30. Spennemann DHR (2006) Freshwater lens, settlement patterns, resource use and connectivity in the Marshall Islands. Transforming Cultures eJournal 1(2):42–63Google Scholar
  31. Terry JP (2007) Tropical cyclones, climatology and impacts in the South Pacific. Springer, New York, 210 ppGoogle Scholar
  32. Terry JP, Thaman RR (2008) Physical geography of Majuro and the Marshall Islands. In: Terry JP, Thomas FR (eds) The Marshall Islands: environment, history and society in the atolls. Faculty of Islands and Oceans, The University of the South Pacific, Suva, Fiji, pp 1–22Google Scholar
  33. Underwood MR, Peterson FL, Voss CL (1992) Groundwater lens dynamics of atoll islands. Water Resour Res 28:2889–2902CrossRefGoogle Scholar
  34. Van Biersel TP, Carlson DA, Milner LR (2007) Impacts of hurricanes storm surges on the groundwater resources. Environ Geol 53:813–826CrossRefGoogle Scholar
  35. van der Velde M, Javaux M, Vanclooster M, Clothier BE (2006) El Niño-Southern oscillation determines the salinity of the freshwater lens under a coral atoll in the Pacific Ocean. Geophys Res Lett 33:L21403.1–L21403.5Google Scholar
  36. Villholth KG, Amerasinghe P, Jeyakumar P (2008) Tsunami impacts on shallow groundwater and associated water supplies on the east coast of Sri Lanka. In: Bhattacharya P, Ramanathan AL, Mukherjee AB, Bundschuh J, Chandrasekharam D, Keshari AK (eds) Groundwater for sustainable development: problems, perspectives and challenges. Taylor and Francis, London, pp 211–222Google Scholar
  37. Webster PJ, Holland GL, Curry JA, Chang H-R (2005) Changes in tropical cyclone number, duration, and intensity in a warming environment. Science 309:1844–1846CrossRefGoogle Scholar
  38. White I, Falkland A, Scott D (1999) Droughts in small coral islands: case study, South Tarawa, Kiribati. Technical documents in hydrology No. 26, IHP-V. UNESCO, Paris, 55 ppGoogle Scholar
  39. White I, Falkland A, Perez P, Dray A, Metutera T, Metai E, Overmars M (2007a) Challenges in freshwater management in low coral atolls. J Clean Prod 15:1522–1528CrossRefGoogle Scholar
  40. White I, Falkland A, Metutera T, Metai E, Overmars M, Perez P, Dray A (2007b) Climatic and human influences on groundwater in low atolls. Vadose Zone J 6:581–590CrossRefGoogle Scholar
  41. White I, Falkland A, Metutera T, Katatia M, Abete-Reema T, Overmars M, Perez P, Dray A (2008) Safe water for people in low, small island Pacific nations: the rural-urban dilemma. Development 51:282–287CrossRefGoogle Scholar
  42. WHO (2006) Guidelines for drinking water quality. First Addendum to the third edition, vol 1, Recommendations. World Health Organization, Geneva, 515 ppGoogle Scholar
  43. Woodroffe CD, Falkland A (1997) Geology and hydrogeology of the Cocos (Keeling) Islands. In: Vacher HL, Quinn TM (eds) Geology and hydrogeology of carbonate islands. Developments in sedimentology, vol 54. Elsevier, Amsterdam, pp 885–908Google Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Department of GeographyNational University of SingaporeKent RidgeSingapore
  2. 2.Island Hydrology ServicesHughesAustralia

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