Groundwater Investigations: German and British

Abstract

Major investigation of groundwater resources in the Channel Islands has taken place in three phases. The first comprised intensive activity by German armed forces in the early 1940s, faced by demographic growth with consequent increased demand for domestic water supplies plus water for mixing considerable quantities of concrete and for optimised agricultural use. The second followed recognition (in Jersey and Guernsey) during a 1976 drought that groundwater resources were finite and might not keep up with future demand. The third responded to a drought from 1989 to 1991. Phase 1 work showed that German geologists and engineers had a thorough understanding of the likely groundwater potential in weathered basement aquifers beneath a thin Quaternary cover, an understanding far in advance of British work elsewhere in the United Kingdom by that time. German investigations in Jersey focused on mapping the different hydraulic properties of the various lithological units that had been recognised earlier, whereas those in Guernsey concentrated on the availability of groundwater and its depth in the low-lying coastal regions of the island. Investigations in both islands used well and borehole inventories as a basic data source together with geological maps and reports. Work in Alderney recognised the poor potential of the shallow bedrock aquifer and recommended the use of horizontal galleries to enhance the area of the abstraction well open to the aquifer. Phase 2 studies, by British civilians, adopted much the same style of investigation, although their emphasis was towards evaluating overall resource potential as well as finding new locations for groundwater development. Phase 3 studies, led by the British Geological Survey, introduced a new investigatory tool, that of hydrochemistry and the distribution of particular chemical ions in order to help determine groundwater flow regimes. Unlike the earlier studies, the phase 3 investigations involved a three-dimensional scheme rather than the two-dimensional mapping framework of the earlier studies, to evaluate the overall productivity of the island aquifers. German maps and reports were not available during phase 2 and 3 studies, but the British work proves that they have stood the test of time extremely well. German work was detailed and thorough and has revealed a remarkably broad extent of technical understanding.