Developing Water Supplies from Saprolite Regolith

Abstract

Extensive areas of saprolite regolith are present on plateau land development over cratonic regions of the earth. These saprolite zones often contain significant water saturated sections and represent large storages of groundwater. Groundwater storages in saprolite, although widely used for village and small rural supplies particularly in subtropical regions where groundwater is at a shallow depth and of low salinity, are rarely developed as a major water source. The principal reason for lack of usage of saprolite groundwater as a major resource results from inherent low to very low hydraulic conductive properties. Much knowledge of saprolite hydrogeology has been gained through development of open pit mines containing these rocks. Long term observations show that a considerable portion of dewatering results from drainage from saprolite rather than from limited storage in fracture zones containing dewatering bores sited in underlying crystalline rock. This paper includes examples taken from widely separate climate regions of the earth where saprolite has been dewatered through use of underdrainage from linear structures in the crystalline bedrock. Underdrainage makes use of both inherent palimpsest structures in saprolite as well as the ‘delayed yield’ factor familiar in development of phreatic aquifers. This underdrainage has resulted in large sustained groundwater yield. Knowledge gained from open pit mine dewatering has provided sound examples for potential extractable storage values from saprolite. This knowledge has proven valuable where applied to planning water supplies from underdeveloped saprolite regions particularly those in arid plateau lands that lack alternative water sources.