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The historical sediment budget Is shown In Table 4. This information is summarized below for 1921 to 1984 water years*. Average Annual Volume (AF): Little Snake 428,000 Yampa L 1 20.000 Combined Rivers 1,548,000 Average Annual Sediment Load (tons): Little Snake 2,020,000 Yampa 389,000 Combined Rivers (supply) 2,409,000 Mathers (capacity) 2.000 Difference (supply - capacity)** 119,000 * These values compare with Table 4 average values rounded off to three significant digits. **This represents an historic 5 percent difference compared to the sediment load at Mathers Hole. The summary shows that the sediment transported through the canyon is ,/in approximate long-term equilibrium with the upstream supply an obvious result considering the long-term adjustment of this river to the geologic and cl imati c conditions (O'Brien, 1984) and the essentially unregulated nature of the f I ow s In the river system. The 5 percent difference between the upstream sediment supply and the load transported at Mathers Hole is within the range of error in the discharge measurements made by O'Brien (1984). The sl ight propensity for sediment storage revealed in Table 4 must be analyzed by reviewing the historical sediment data for the Little Snake and Yampa Rivers on which the predictive regression relationships are based. From Table 1 the sediment data was collected for years that on the average were only 77 percent of mean vol ume for the Yampa and 73 percent for the Little Snake. Th i s data was col I ected on the average dur i ng dry per i ods. This is difficult to interpret, because In Table 1 It Is noted that the measured sediment load in the wet years was from 5 to 8 times the measured sediment load In the drier years. These dr i er years may have hel ped produce more sediment I oad In the wet years. More sediment data Is necessary to concl ude that the system Is aggradi ng or degrading over the I ong term and the best interpretation Is that barring any dramatic ci imate changes relative eq u i I i br i um has been established. Exceedance f lows for a range of probabi l iti es were cal cul ated as discussed in the Procedure and are presented In Appendix A. These exceedance hydrographs were input as minimum streamflow hydrographs together 12