Hydrology of Small Oceanic Islands — Utility of an Estimate of Recharge Inferred from the Chloride Concentration of the Freshwater Lenses

Authors

• H. L. Vacher, Washington State UniversityFollow
• J. F. Ayers, Washington State University

Document Type

Article

Publication Date

1-1980

Digital Object Identifier (DOI)

https://doi.org/10.1016/0022-1694(80)90003-7

Abstract

In Bermuda, as in other coastal and oceanic-island environments, rainfall has a significant chloride concentration. As a result, there is a relatively straightforward way of estimating groundwater recharge by considering the Cl⁻ ion as a tracer which is concentrated by evapotranspiration.

The Cl⁻ concentration of rainfall in Bermuda is about 15 ppm. That of the freshest part of the largest Ghyben-Herzberg lens is about 60 ppm. Taking the 60 ppm value as an indicator of the Cl⁻concentration of recharge, the average recharge rate is estimated at 0.25 of the 147-cm/yr. average rainfall, or about 37 cm/yr.

This estimate is similar to two other estimates of recharge in Bermuda, each derived from hydrogeologic field data:

(1) A 33-cm/yr. estimate inferred from a 2·10⁶-m² area of diversion in which: (a) outflows (extractions) are 2870 m³/day; and (b) the change in storage is estimated at 1100 m³/day, from the rate of lowering of the water table.

(2) An estimate of 35 to 45 cm/yr. resulting from combination of: (a) the ratio of recharge to hydraulic conductivity of the Paget Formation (12·10⁻⁶), determined from the configuration of the Ghyben-Herzberg lenses; and (b) the hydraulic conductivity of the Paget Formation (85–100 m/day), estimated from the behavior of the water table.

The agreement between the three estimates of recharge indicates that the rather simple and inexpensive technique of calculating recharge from Cl⁻ content of rainfall and fresh groundwater can be a useful addition to the arsenal of techniques by which recharge of small oceanic islands can be evaluated.

Was this content written or created while at USF?

No

Citation / Publisher Attribution

Journal of Hydrology, v. 45, issues 1-2, p. 21-37

Scholar Commons Citation

Vacher, H. L. and Ayers, J. F., "Hydrology of Small Oceanic Islands — Utility of an Estimate of Recharge Inferred from the Chloride Concentration of the Freshwater Lenses" (1980). School of Geosciences Faculty and Staff Publications. 1865.
https://digitalcommons.usf.edu/geo_facpub/1865