WEST INDIES 1

ABSTRACT: Repeated measurements of in situ water resistance were taken from tmcased boreholes m the unconfined carbonate aquifer along the southwest coast of Barbados, W. I. during a two-year period from 1969-1971. With these data we can interpret he position of the fresh/salt water interface within the aquifer; monitor seasonal variations in the thickness of the fresh water lens; and note perturbations of the spacial position of, the fresh water lens within the aquifer which may be associated with unusual climatic events. The coastal fresh water lens of Barbados varies in thickness both spatially and temporally from one to greater than 10 m, but averages about 7 m. A zone of diffusion or mixing, 0.1 to 12.8 m thick, separates the fresh water from underlying marine derived waters. Average seepage velocities of the fresh ground water were calculated using average rates of recharge, rock porosity, and lens thickness, to be 43-143 m/yr. However, following periods of high recharge, seepage velocities may exceed several thousand m/yr. Various subenvironments within the fresh water lens and associated mixing zone may migrate through considerable thickness of the upper portion of the saturated zone in the coastal aquifer of Barbados. Dissolution and/or precipitation of carbonate phases may occur during different periods of the recharge cycle throughout the entire thickness of the fresh water portion of the aquifer