Rate-based estimation of the runoff coefficients for selected watersheds in Texas

Nirajan Dhakal, Xing Fang, William H. Asquith, Theodore G. Cleveland, David B. Thompson

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


The runoff coefficient, C, of the rational method is an expression of rate proportionality between rainfall intensity and peak discharge. Values of C were derived for 80 developed and undeveloped watersheds in Texas using two distinct methods. First, the ratebased runoff coefficient, Crate, was estimated for each of about 1,500 rainfall-runoff events. Second, the frequency-matching approach was used to derive a runoff coefficient, Cr, for each watershed. Published C values, Clit, or literature-based runoff coefficients were compared to those obtained from the methods investigated here. Using the 80 Texas watersheds, comparison of the two methods shows that about 75% of literature-based runoff coefficients are greater than Cr and the watershed-median Crate, but for developed watersheds with more impervious cover, literature-based runoff coefficients are less than Cr and Crate. An equation applicable to many Texas watersheds is proposed to estimate C as a function of impervious area.

Original languageEnglish
Pages (from-to)1571-1580
Number of pages10
JournalJournal of Hydrologic Engineering
Issue number12
StatePublished - 2013


  • Frequency matching
  • Peak discharge
  • Rate-based runoff coefficient
  • Rational method
  • Runoff
  • Surface hydrology


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