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NII4ME'rrIlS ,." NOIf-ANWHNT J/IfIAJtU4T/ON PA1I4M. 'irS - HYJ)1I06114~H ~~ MASS CVIIYE' OF 114INF41.1. 4.-, SE'IIIE'$ 4000 W4rcIlSHE'D //lAME' 4Nb I.Dt:4TION NDN-4APA,lfCNT f/JItJANq4T1O/N NII,u,cf'E'1I, .- C4110S 6tJOO.89:H , CAllOS ItJOt)-UJ1J1 , CAllOS "OOO-~J1J1 . 4NNlUl FI.OOI1 '-E'41f SE'INE'S s IUrE'IISNE'O OE'SCRI.-TlOIII 0000 I UA8Il"llZATIOfII PAIIAI<<TEII$ NOT APPARENT ON AE'U,lll PHOTOlOII.IlPH$. Z URtlANIZATlON PIllIIAIIIHEIIS IIUSUIIEO FIIOM AEIII"L PMOTMflA~H$. ~ HYORQGR..PH FOil flllST EVENT. .. MASS GIIAPH fOil fiRST EVENT. S "'PI fOf! flllST EVENT. Fig. 2. Schematic Representation of Data Arrangement for a Single Watershed with Two Runoff Events Unit Hyd40g~ph Peak.-The peak values of the unit hydrograph and the estimated time to peak were then used to obtain regression relationships to determine the reliability of these unit hydrograph parameters. Since no outliers were found in the residuals it was concluded that the data used were adequate for the estimation of the parameters. To avoid the possibility that the tool used in the determination of the unit hydrographs was inadequate. three computer programs were used to derive the unit hydrographs and their results compared as explained later in. the text. Graphs of the observed. the computed and the unit hydrographs used are given in Appendix C. The determination of the time to peak was sensi- tive to the interval chosen because the peak of the unit hydrograph could occur sometime within the five- minute interval. Two values of the time to peak were obtained and their performance on the regression analysis evaluated. The first value used was the interval between the beginning of the rainfall excess to the beginning of the largest five-minute runoff volume. The second value was obtained by estimating the possible location of the peak when the trends of the ordinates on both sides of the peak were extended to intersect at the peak. The second procedure pro- duced smaller values of the standard error of estimate and was adopted for use in this investigation. R~pon6e Time. -- The importance of a watershed response t1me has been recognized since the time of Mulvaney in 1851. The concept of response time has acquired many different definitions. A general defi- nition for the Response Time of the watershed is the significant length of time required for a watershed to respond to a uniform input of rainfall excess. The rainfall excess is defined as the rainfall which excess to that which will infiltrate into the soil. Lopez (1973) determined the watershed response times utilizing eight different ways of defining the response time. The particular definition of the re- sponse time which will be selected will be the one which has the highest correlation with the physical watershed and storm characteristics. The definitions and symbols for the Response time is given in Table 5. Lopez used different symbols. His symbols are given in parentheses. These different time intervals are depicted on Figs. 3, 4. and S. The values of these time variables are given in Table 6. Q DtrKtRurloff Hydrogrlph Fig. 3. Definition Sketch for Time to Peak IS