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and K. The regression constant C is included in the nomograph by the positioning of each T-year variable. The simplified equations used to determine the nomograph were; Q'0 1150 A.78 K.36 Q2S = 1460 A,78 K.36 Qso = 1660 A.78 K.36 Q'00= 1870 A.78 K.36 EFFECT OF URBANIZATION ON FLOOD RUNOFF Changes in Flood Peaks Solutions to equations in table 10 can yield the following analogies; 1. When the imperviousness is increased from 0 to 40 percent, Q2 is increased about 35 percent, Q'0 is increased about 18 percent, and Qso is increased about 16 percent. 2. When the imperviousness is increased from 0 to 100 percent, Q2 is increased about 80 percent, Q'0 is increased about 40 percent, and Qso is increased about 35 percent. 3. When L is decreased and (or) S is increased, the T-year flood is increased. These analogies are consistent with the results found in hydrologic studies of other urban areas. However, the degree of the effect of imper- vious area on peak discharge is not as great in Dallas as it is in Houston (Johnson and Sayre, 1973) or other coastal areas. A comparison of the 50- year peak discharges, as a result of urbanization in the Dallas and Houston areas is shown on figure 9. As indicated by figure 9, the channe'ls in Dallas, even before urbanization, are capable of much better conveyance of floods than are the channels in the Houston area even after urbanization. The small increase in the magnitude of peak discharges in the Dallas area after urbanization may be caused by the following factors; 1. The channel conveyance conditions before urbanization are good, with the channels relatively straight and free of vegetation. 2. The soil cover in the Dallas area is thin. 3. Both side and channel slopes are relatively steep. -45-