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 2·10 6 -m 2 area of diversion in which: (a) outflows (extractions) are 2870 m 3 /day; and (b) the change in storage is estimated at 1100 m 3 /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.
Original language | American English |
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Journal | Journal of Hydrology |
Volume | 45 |
DOIs | |
State | Published - Jan 1 1980 |
Externally published | Yes |
Disciplines
- Earth Sciences