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Geological Occurrence of Groundwater

Ground Water Hydrology

  1. John E. Moore

Published Online: 15 APR 2005

DOI: 10.1002/047147844X.gw271

Water Encyclopedia

Water Encyclopedia

How to Cite

Moore, J. E. 2005. Geological Occurrence of Groundwater. Water Encyclopedia. 5:145.

Author Information

  1. USGS (Retired), Denver, Colorado

Publication History

  1. Published Online: 15 APR 2005

Abstract

The occurrence, movement, and storage of groundwater are controlled by geology. The geologic factors that control groundwater are petrography, stratigraphy, structure, geomorphology, lithology, and thickness. The petrography of a given rock type controls the porosity and permeability. Porosity defines the storage capacity of an aquifer. There are two types of porosity: primary and secondary. Primary porosity, such as pores between sand grains, is created when rocks are formed. The shape, sorting, and packing of grains determine primary porosity. Sedimentary rocks are poorly sorted when the grains are not the same size creating spaces between the larger grains that are filled by smaller grains. Secondary porosity such as joints, fractures, and solution opening, is formed after the rock has been deposited. The number and arrangement of fracture openings and the degree to which they are filled with fine-grained material control secondary porosity.

Keywords:

  • confined aquifer;
  • unconfined aquifer;
  • aquifer;
  • continuing zone