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111 Rainfall Excess Overland Flow

Part 10. Rainfall-Runoff Processes

  1. Roger E Smith1,
  2. David C Goodrich2

Published Online: 15 APR 2006

DOI: 10.1002/0470848944.hsa117

Encyclopedia of Hydrological Sciences

Encyclopedia of Hydrological Sciences

How to Cite

Smith, R. E. and Goodrich, D. C. 2006. Rainfall Excess Overland Flow. Encyclopedia of Hydrological Sciences. 10:111.

Author Information

  1. 1

    Colorado State University, Civil Engineering Department, Fort Collins, CO, US

  2. 2

    ARS USDA, Southwest Watershed Research Center, Tucson, AZ, US

Publication History

  1. Published Online: 15 APR 2006


One of the processes that can generate surface runoff is rainfall excess, which is a process controlled at the surface of the soil. This occurs when rainfall reaches the soil at a rate in excess of the soil's ability to absorb, which is called infiltrability. This dynamic property can in uniform soil be described by a rather well-developed infiltration theory. Surface water flow toward a receiving channel may in geometrically simple conditions be described by the kinematic or diffusive wave equations. The surface water is in continuous interaction with the soil's changing infiltrability. Both infiltration theory and surface flow equations are introduced here, and the interactions and complexities arising from spatial variations are discussed. These processes are incorporated in modern hydrologic response models, using numerical solutions as well as analytic solutions. The application of this theory in hydrology, however, must be informed by scale considerations and the appropriate treatment of natural complexities. Some scale limitations and some approximate methods for treating spatial soil variations are illustrated in this article, with reference to relevant literature.


  • runoff;
  • infiltration;
  • hydrology;
  • overland flow;
  • kinematic wave