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150 Unsaturated Zone Flow Processes

Part 13. Groundwater

  1. John R Nimmo

Published Online: 15 APR 2006

DOI: 10.1002/0470848944.hsa161

Encyclopedia of Hydrological Sciences

Encyclopedia of Hydrological Sciences

How to Cite

Nimmo, J. R. 2006. Unsaturated Zone Flow Processes. Encyclopedia of Hydrological Sciences. 13:150.

Author Information

  1. United States Geological Survey, Menlo Park, CA, US

Publication History

  1. Published Online: 15 APR 2006


Water flow in the unsaturated zone is greatly influenced by unsaturated hydrostatics (water content, energy, pressure, and retention) and by unsaturated hydrodynamics (diffuse flow and preferential flow). Important multiphase processes include the transport of gases, nonaqueous liquids, and solid particles. Numerous means are available for determination of unsaturated conditions and properties, both measurement (of moisture state, water retention, and dynamic characteristics) and through various formulas and models that are mostly empirical in nature, but in some cases incorporating insight into unsaturated-zone physical processes. Applications to practical problems include models and techniques relating to distributions of water and energy, fluxes at the land surface, inputs, outputs, and fluxes within the unsaturated zone, all of which are frequently complicated by heterogeneity and preferential flow. Further scientific advance requires new measurement techniques and theoretical constructs that more adequately represent the important physical processes within practical modeling schemes.


  • unsaturated flow;
  • tranport phenomnena;
  • ground water;
  • soil moisture;
  • unsaturated zone;
  • vadose zone;
  • hydraulic properties;
  • multiphase flow