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4.0 QUANTITATIVE CHARACTERISTICS OF STREAMFLOW 4.1 Monthlg Flow Variation STREAMFLOW VARIES SEASONALLY IN MOST STREAMS Most of the streamflow in the White River occurs during the spring. Streamflow in Piceance Creek is distributed more uniformly throughout the year. Most streamflow within the White River basin occurs during the spring as a result of snowmelt runoff, as illustrated in figure 4.1-1. For example, at the mouth of the Whi te Ri ver, about 65 percent of the annual fl ow occurs during May, June, and July; and upstream, 75 percent of the flow occurs in the South Fork White River, near Buford, Colo., during the period. The South Fork station is at a higher elevation, and the larger streamflow percentage reflects a greater contribution from snowmelt runoff. The monthly data summary for the Piceance Creek station illustrates a more uniform distribution of streamfl ow throughout each year and a 1 ess pronounced effect of snowme 1 t runoff in the spring. A box plot provides a method to summarize a set of data in terms of a few easily obtained and understood numbers. The range of data is represented by its extremes, that is, the smallest and largest values. On the example plots of monthly streamflow (fig. 4.1-1), the extremes are depicted by the short horizontal lines at the ends of the dashed lines for each month. The median is shown as the hori zonta 1 1 i ne ins i de each box plot and the upper and lower boundari es of each box depi ct the 25th and 75th percentiles of the gi ven monthly data. Twenty-five percent of the data values are less than the 25th percent il e and 25 percent of the data values are greater than the 75th percent i 1 e. The differences between the percent i 1 e values and the medi an value indicate the distribution of the data about the median value. 14