Crystalline Rock Aquifers, A Global View

 

Crystalline Rock Aquifers, A Global View

Approximately 30 percent of the world’s land mass is underlain by crystalline igneous and metamorphic rocks that occur in a wide variety of physiographic and climatic regions ranging from hilly mountainous terrains to relatively flat plains and from arid regions to tropical areas with considerable precipitation.

Aquifer hydraulic characteristics for several regions of the world indicate that variations in well yield, transmissivity, and specific capacity are generally comparable for different crystalline rock types.  Variations in climatic conditions control the amount of groundwater that can sustainably be extracted from crystalline rock aquifer systems on an annual basis.

Four basic criteria were evaluated to develop an understanding and comparison of yield and water-bearing characteristics of crystalline rock aquifers globally:  1. The effect of topography on well yields; 2. The distribution of well yields (histograms) in different crystalline rock types for selected areas of the world; 3. The effect of well depth on well yields and an evaluation of incremental well yields with increasing well depth; and 4. The distribution of specific capacity frequency for selected areas of the world.

Based on an analysis of data from several regions of the world, well yields were found to range over three orders of magnitude from less than 0.06 liters per second (lps) to more than 6.3 lps and transmissivity from less than 1.25 meters squared per day (m²/day) to more than 500 m²/day. 

The management of aquifer systems in crystalline rocks is challenging given the relatively low aquifer storage and low to moderate well yields.  Planning and development programs need to take into consideration the sensitivity of crystalline rock aquifer systems to droughts.