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4.0 QUANTITATIVE CHARACTERISTICS OF STREAMFLOW--Continued 4.2 Low Flow and High Flow LOW-FLOW AND HIGH-FLOW CHARACTERISTICS VARY MARKEDLY The low-flow values are smaller in the western part of the basin than in the eastern part. The high-flow values generally are larger for stations at lower elevations. Areal variations of selected streamflow characteristics are indicated in table 4.2-1 for 25 mainstem and tributary stations in the White River basin. These stations were se 1 ected at vari ous 1 ocat ions to represent a range of climatic, geologic, and vegetative conditions. The average annual flow per square mile of drainage area varies considerably within the basin. The larger values generally are characteristic of streams at the higher elevations in the eastern part of the basin and primarily reflect the larger quantities of annual precipitation. The smaller va 1 ues are characteri st i c of streams in the western part of the bas in where annual precipitation is smaller. Low-flow characteristics commonly are used to evaluate the adequacy of a stream to assimilate industrial or municipal wastes or both, to preserve a suitable aquatic environment, and to fulfill water-supply requirements. A common low-flow statistic used for this is the 7-day low flow that occurs, on the average, once every 10 years. This particular low-flow statistic varied markedly for the stations analyzed. The 7-day, 10-year low-flow discharges per square mil e are 1 arger in the eastern part of the bas in than in the western part because many of the streams in the western part do not flow for part of the year. High-flow characteristics commonly are used to evaluate flood-flow frequencies and to determine flood plains. High-flow values result from snowmelt or from thunderstorms; The I-day, high-flow discharges that occur, on the average, once every 25 years, vary throughout the basin but mainly are greater in the eastern part than in the western part. The 1 argest hi gh-fl ow discharges in the White River basin usually result from thunderstorms, which generally do not occur at stations at the higher elevations; snowmelt runoff usually produces the maximum streamflow each year for these stations. High flows at stations at the lower elevations can result either from snowmelt or from thunderstorms. 16