Changes of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments
Hydrogeology Journal
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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.
Suggested Citation
Rotzoll, K., Oki, D.S., El-Kadi, A.I., 2010, Changes of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments: Hydrogeology Journal, v. 18, no. 6, p. 1425-1436, https://doi.org/10.1007/s10040-010-0602-4.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Changes of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments |
| Series title | Hydrogeology Journal |
| DOI | 10.1007/s10040-010-0602-4 |
| Volume | 18 |
| Issue | 6 |
| Publication Date | April 29, 2010 |
| Year Published | 2010 |
| Language | English |
| Publisher | Springer |
| Contributing office(s) | Pacific Islands Water Science Center |
| Description | 12 p. |
| First page | 1425 |
| Last page | 1436 |
| Time Range Start | 1999-01-01 |
| Time Range End | 2009-12-31 |
| Country | United States |
| State | Hawai'i |