Water Resources Management

, Volume 20, Issue 5, pp 643–660

An Improved IaS Relation Incorporating Antecedent Moisture in SCS-CN Methodology


    • Department of Water Resources Development and ManagementIndian Institute of Technology
  • R. K. Sahu
    • Department of Civil EngineeringIndian Institute of Technology Bombay
  • T. I. Eldho
    • Department of Civil EngineeringIndian Institute of Technology Bombay
  • M. K. Jain
    • National Institute of Hydrology

DOI: 10.1007/s11269-005-9000-4

Cite this article as:
Mishra, S.K., Sahu, R.K., Eldho, T.I. et al. Water Resour Manage (2006) 20: 643. doi:10.1007/s11269-005-9000-4


Employing a large dataset of 84 small watersheds (area = 0.17 to 71.99 ha) of U.S.A., this paper investigates a number of initial abstraction (Ia)-potential maximum retention (S) relations incorporating antecedent moisture (M) as a function of antecedent precipitation (P5), and finally suggests an improved relation for use in the popular Soil Conservation Service Curve Number (SCS-CN) methodology for determination of direct runoff from given rainfall. The improved performance of the incorporated M = α \(sqrt{P_5S}\) and Ia = λ S2/(S + M) relations, where λ is the initial abstraction coefficient, in the SCS-CN methodology exhibits the dependence of Ia on M, which is close to reality; the larger the M, the lesser will be Ia, and vice versa. Such incorporation obviates sudden jumps in the curve number variation with antecedent moisture condition, an unreasonable and undesirable feature of the existing SCS-CN model.

Key words

antecedent moisturecurve numberinitial abstractionNEH-4soil conservation service

Copyright information

© Springer Science+Business Media, Inc. 2006