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TABLE 1. Discharge Ranges, Recurrence Intervals, and Flow-Related Factors. [m3/s, cubic meters per second; RI, flood recurrence interval; d50, median grain size] 1911-1965 1966-1993 Contemporary flow-related factors: Discharge recurrence recurrence Geomorphic and sedimentologic conditions; range interval interval user demand and effect on natural resources Less than Yearly Yearly Below bankfull discharge, rocks exposed in rapids. 30 m3/s Large boats impeded, rafting parties decline, wading enhanced. Excellent fishing. Warm temperature promotes algal growth and increased turbidity. Fine sediment from tributaries kills fish and accumulates. Occurs in spring and fall in average year. 30 to Yearly Yearly to Just below bankfull discharge, (62 m 3/S), to bank 85 rn 1.7 years inundation. Fine sediments flushed from riffles; moderate velocities and abundant eddies. Excellent rafting, multiday trips, good fishing if steady flow sustained. Cool temperatures favor trout. Large number of hike-in users. Optimal conditions for most user types (July, August). Greatest user conflict, resource stress, and management demands. 85 to Yearly to 1.7 to High flow, faster velocities, local gravel and cobble 140 m3/s 1.2 years 4 years bed entrainment, but low turbidity. Low grassy terraces, camps, trails inundated; restricted access. Commercial and private multiday fishing trips decline. Whitewater conditions good. 140 to 1.2 to 4 to Very high flow, Crystal Reservoir spills. Only 5 times 250 m3/s 2 years 20 years since 1966. Pre-regulation bankfull discharge (1.3- year RI). Midlevel willow terraces inundated. Local reworking of some debris-flow material in rapids. Bed d5o may be entrained in many riffle reaches. Whitewater conditions-require more technical skill. - Rafting trips decline for safety concerns. Limited bank access and poor fishing conditions. More than More than More than Rare flows since regulation (1970, 1983, 1984). 250 m3/s 2 years 20 years Juniper-stage discharge (310 m3/s) had 3.2-year RI before 1966. Inundation of box elder and lowest Utah juniper trees. Possible changes in channel cross-section and bed-material size distribution. Possible scouring of some low terrace vegetation. Whitewater conditions very technical, hazardous.