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

Nirajan Dhakal, Xing Fang, William Asquith, Theodore Cleveland, David Thompson

Research output: Contribution to journalArticlepeer-review


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, C rate , was estimated for each of about 1,500 rainfall-runoff events. Second, the frequency-matching approach was used to derive a runoff coefficient, C r , for each watershed. Published C values, C lit , 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 C r and the watershed-median C rate , but for developed watersheds with more impervious cover, literature-based runoff coefficients are less than C r and C rate . An equation applicable to many Texas watersheds is proposed to estimate C as a function of imper
Original languageEnglish
Pages (from-to)1571–1580
JournalJournal of Hydrologic Engineering
StatePublished - Nov 26 2013


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