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~23 of the distribution of daily mean streamflows was computed as: SK = f (Q - Q)3 p(Q) dQ / [f (Q - Q)2 p(Q) dQ] 3/2 (3) where Q = discharge, in m3/s; and p( Q) = cumulative-density duration .of dis- charge. Both Wolman and Miller (1960) and Baker (1977) have noted that the skew of the distribution of stream flows increases with decreasing drainage area. The skews of streamflow at the 15 Yampa River basin gaging stations are plotted against the contributing drainage areas in Fig. 7. As expected, the skews are inversely related to drainage areas. The agreement is quite good and differences in climate between the several watersheds do not appear to be significant. The relative thresholds of sediment movement at the gaging stations were approximated by the ratio of the median diameter of bed material to the stream power per unit width at the effective discharge. The possible signifi- cance of streamflow variability and the threshold of sediment movement upon the frequency of the effective discharge was tested by a multiple regression correlation between the duration of effective discharge and the skew of stream- flow and Dso/-r qeff S was computed. The effective-discharge duration and skews were related; however, no improvement in the correlation was obtained by addition of the Dsoh qeff S ratio. The relation between effective-discharge duration and streamflow skew is shown in Fig. 8. Variation in streamflow 5 W ~ cr < J:UJ ~~ Qi= UJu.. >0 -w .....~ ~< u....... u..z UJUJ u..U ocr UJ za.. OZ 0.5 i=- < cr :;) 0 0.2 0.2 . . 40 0.5 1 5 10 SKEW OF DAILY MEAN STREAMFLOW Fig. 8. Relation between the skew of daily mean discharges and the duration of the effect- ive discharge.