| Abstract: | Freshwater-lens thickness and long-term changes in freshwater volume in coastal aquifers are commonly assessed through repeated measurement of salinity profiles from monitor wells that penetrate into underlying salt water. In Hawaii, the thickest measured freshwater lens is currently 262 m in dike-free, volcanic-rock aquifers that are overlain by thick coastal sediments. The midpoint depth (depth where salinity is 50% salt water) between freshwater and salt water can serve as an indicator for freshwater thickness. Most measured midpoints have risen over the past 40 years, indicating a shrinking lens. The mean rate of rise of the midpoint from 1999–2009 varied locally, with faster rates in highly developed areas (1.0 m/year) and slower rates in less developed areas (0.5 m/year). The thinning of the freshwater lenses is the result of long-term groundwater withdrawal and reduced recharge. Freshwater/salt-water interface locations predicted from measured water levels and the Ghyben-Herzberg principle may be deeper than measured midpoints during some periods and shallower during other periods, although depths may differ up to 100 m in some cases. Moreover, changes in the midpoint are slower than changes in water level. Thus, water levels may not be a reliable indicator of the amount of freshwater in a coastal aquifer. |
| Genre: | Article |
| ProdID: | 70005463 |
| Citation Author: | Rotzoll, Kolja ; Oki, Delwyn S.; El-Kadi, Aly I. |
| Citation Contributing Office: | Pacific Islands Water Science Center |
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| Citation End Page: | 1436 |
| Citation Issue: | 6 |
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| Citation Language: | English |
| Citation Larger Work Title: | Hydrogeology Journal |
| Citation LatN: | 0214400 |
| Citation LatS: | 0211500 |
| Citation LonE: | -1574000 |
| Citation LonW: | -1581000 |
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| Citation Online Only Flag: | |
| Citation Phsyical Description: | 12 p. |
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| Citation Publisher: | Springer |
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| Citation Search Results Text: | Changes of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments; 2010; Article; Journal; Hydrogeology Journal; Rotzoll, Kolja ; Oki, Delwyn S.; El-Kadi, Aly I. |
| Citation Start Page: | 1425 |
| Citation Volume: | 18 |
| Citation Year: | 2010 |
| Type: | citation/reference |
| Text: | Changes of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments; 2010; Article; Journal; Hydrogeology Journal; Rotzoll, Kolja ; Oki, Delwyn S.; El-Kadi, Aly I. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (INDEX PAGE): | http://www.springerlink.com/content/5l464400tu175261/ |
| Date Other: | Wed, 28 Sep 2011 00:00 -0500 |
| Publisher: | Springer |
