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n L Lea IS (Eagleson) The disadvantage to all of the watershed parameters used is that they have dimensions. There is consider- able advantage if these could be dimensionless num~. Eagleson used the lag curve developed in the Los Angeles District Office of the Corps of Engineers and shown in Linsley et aI. (1958). Eagleson gave these equations for basin lag in terms of the basin para- meter, 12: \B 1.2 nO.38 Mountain Drainage \B 0.72 nO.38 Foothill Drainage \B 0.35 nO.38 Valley Drainage TLB 0.18 nO.38 Urban Drainage (Louisville) where TLB cess to the is the time from beginning of rainfall centroid of the runoff hydro graph, n L Lea/IS The coefficients in the lag relationships are aaalo- gaus to the C defined by Snyder (1938) however, they are not e&uivalent to Snyder's Ct because origi- nally Snyder did not include the slope term in his basin parameter. Linsley. Kohler and Paulhus (1958) and Eagleson (1962) give the exponent on the basin para- meter as 0.38. Various flood studies published by the Corps of Engineers and the Bureau of Reclamation show values of this exponent between 0.30 and 0.38. The lag time, as defined by Eagleson, is one way to define the watershed response time. Wilson (1972) carried out an investigation on watershed response time in an effort to establish interrelationships for the various definitions of response time. The re- sponse time of the watersheJ is defined as the signi- ficant length of time required for a watershed to respond to a uniform input of rainfall excess. The various ways to quantify the response time were examined and compared by Espey. Morgan and Masch (1965), Wilson (1972) and others. These are presented later in this report in Table 5. Wilson's (1972) investigatioil was based entirely on data from pristine watersheds. It remains to be established which is the most effective way to define the response time for an urban ....atershed. Regardless of the exact form of the definitioil of the response time. it is clear that the response time is related to either the ba~i~ parameter of Eagleson: L L 11 ----f.! is or Carter's length-slope parameter: 1... is Sarma, Delleur and Rao (1969) conducted a re- search project on analytical models for simulating the effect of urbanization on runoff. Data from four ur- ban watersheds near Purdue University were supplement- ed with data from other Indiana and Texas watersheds. Four conceptual models were used in the analysis of the data: 1) Single Linear Reservoir Model. 2) Double Routing Method. 3) Nash Model, 4) Single Linear Reservoir with a Linear Channel model. It was found that for watersheds smaller than five square miles in size, the single linear reservoir pro- vided best reproducibility of the recorded floods. The Nash Model best simulated the rainfall-runoff pro- cess on larger watersheds (between 5 and 20 square miles in size). Sarma, Delleur and Rao (1969) used a multiple re- gression technique to find relationships between phy- sical watershed parameters, urbanization parameters and unit hydro graph parameters: 1) Lag Time, 2) Time to Peak. 3) Peak Discharge, 4) Frequency of Peak Discharge. ex- Narayana, Sial. Riley and Israelsen (1970) car- ried out a similar study utilizing a larger data base. They analyzed the results of 200 events from SO rural watersheds and 193 events from 20 urban watersheds. Narayana et al., limited their research to developing relationships between watershed. storm and urbaniza- tion factors and the peak discharge and the total vol- ume of runoff. No relationships were developed be- tween the watershed response time and the physical watershed and storm parameters. A log transformed model was found to give the best results. The peak discharge was estimated by: Qp = 0.777 W1S1U1 \..here tv, is the watershed parameter tv, AO, 73850, 206 Lo.042 5, is the storm parameter pl.016pO.l79 5, 30 DO.26 ", is the urbanization parameter "1 1 1.280,797 > cf A is watershed area in acres S is main channel slope in percent L is main channel length in miles p is the total storm rainfall in inches P30 is the maximum 30 minute rainfall D is the storm duration in hours 9