Between 1980 and 1989 Jasminko Karanjac worked as hydrogeologist and groundwater modeling consultant in the UNDP-financed projects in Bermuda coded BER/79/002 and BER/86/001. The title of the first project was "Groundwater Resources Development and Management," and of the second "Advanced Fresh Water Lens Modeling and Groundwater Software Development."
All the land mass of Bermuda is underlain with groundwater. The quality of the water varies according to depth, distance from the shoreline, and the type of geological strata at sea level. The variation is from near sea water quality of total dissolved solids (TDS) 35,500 parts per million (ppm), to potable water of TDS 400 ppm. Although fresh water may be available over a large area, the development of a sizable volume of that water is a very risky undertaking, which may rapidly lead to the deterioration of the supply.
The islands of Bermuda are formed of sedimentary limestone bedrock laid down on an extinct volcanic pinnacle. Borings have located the volcanic rock at a depth of 200 ft. below sea level. The limestones are cyclically alternating with paleosoils. In Bermuda, the characteristics of limestone rocks are such that the water-holding rocks can properly be labeled as a microkarstic environment. Classical pumping tests, at a very low rate in order not to create the upconing of brackish or saline water, cannot create any appreciable depression in such a highly permeable medium. The modeling exercise, i.e. calibration of the model to match the historic water table configuration, was the only source which produced at least a range of values for aquifer transmissivities.
The preliminary management model of the Central Lens of Bermuda was of value in drawing attention to: (1) reliability of water level measurements; (2) the effect of urbanization on recharge; (3) details of abstraction quantities and artificial recharge activities; (4) information on aquifer characteristics from recently cored boreholes; (5) relation between the aquifer and marsh bodies; and (6) effect of large abstractions for flushing water and air conditioning coolant. The model was successfully used to examine a number of aquifer management possibilities. On the basis of the results, a policy of maximum abstraction of up to 2 mgd was proposed, which flattens the central part of the water table, reduces seaward flow, and thins out the fresh-water aquifer. The scenario of developing 2 mgd is quite a workable one from the point of view of resources alone. However, the increased contribution of domestic waste water and road run-off to recharge, coupled with the policy of maximum abstraction, would increase the vulnerability of the lens to pollution and would reduce the options available to manage polluted areas.
This UNDP project was of direct benefit to other small islands and not only to Bermuda. The Interregional Seminar on Islands Groundwater Development and Management, organized by the project and hosted by the Bermuda Government in Bermuda in December 1985, provided a forum for exchange of information about hydrogeology and modeling of small islands. The islands of Bermuda served as a model on their own, showing how drinking water supply problems can be solved in an integrated way, utilizing, by means of sophisticated technology and instrumentation, all kinds of available water.
In the second phase of the project, between 1986 and 1989, a new software package has been developed. The package known as the United Nations Ground Water Software, of which J.Karanjac is the principal author, includes, among other programs, a module for modeling a fresh water lens on a small island. The module features the sea water - fresh water interface, the constant-head dynamic sea level boundaries, and the space and time variable Ghyben-Herzberg ratio.