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16 inflow or stream losses occur in the intervening reach and therefore, the gaging station flows represent the inflow to the Monument. On the average, the USGS discharge computed by combining the discharge at the stations is slightly higher than that discharge measured at Mathers Hole (see Figure 6). This comparison is only relative, however, being a function of the flow travel time, the time of day that the discharge measurements are made and the magnitude of the unsteadiness of the flow. The average difference of 6.5% (absolute) between the discharges gives credibility to stage-discharge relationship at Mathers Hole. The 1983 Yampa River discharge and the mean annual discharge are shown in Figures 7 and 8. The mean annual discharge was calculated using the period 1941-83. The period from 1922-83 constitutes the entire period of record. The first 20 years of this record were wetter than the remaining 40, and the 1941-83 period is more representative of the conditions that exist today in the Yampa River (USGS, John Elliott, personal communication, 2/83). Table I reveals the marked difference between the periods. The lower discharge period, 1941-1983, has a mean water yield of 1,483,700 acre-feet, compared to 1,508,400 acre-feet for the entire period of record. Figures 9 and 10 are plots of the five and ten year running average of the annual volumes of the Yampa River at Deerlodge. The climate was drier than normal from about 1935 through 1965. The 1920's and 1965- 1975 are wet periods which offset the dry period in the 1930's and 40's. The period of record is too short to discern any distinct cycles. The sediment record for the Little Snake, however, occurs during a drier than average period. It is difficult to speculate on the relative magnitude of sediment yield during dry or wet periods but generally, in semiarid regions, a decrease in runoff retards erosion. Instantaneous peak discharges are generally used to estimate discharge frequency. Since the flows from the two gaging stations are combined to determine the mean daily discharge at Deerlodge Park, the use of instantaneous peak discharges is inappropriate. Discharges of a specified return period are determined by the application of a theoretical probability distribution. Richards (1982) reports that the Gumbel Extreme Value distribution is a model which generates a linear function on a transformed probability scale. It is a two parameter model which seems to yield more representative values for the Yampa River than the log-Pearson type III model. The results of the Gumbel distribution and log-Pearson type III are shown in Table II. The Gumbel distribution is plotted in Figure 11. The 1983 peak discharge of 20,300 cfs has a return period of approximately 13 years based on the Gumbel analysis and over 20 years based on the log-Pearson type III. Four discharges in 62 years have exceeded 20,000 cfs which is a return period of about 15 years. The maximum recorded peak discharge was 21,750 cfs in 1974 (see Table III). The one hundred year event is about 27,000 (Gumbel) and 22,000 cfs (Pearson). The 1983 Yampa River hydrograph in the Monument had the fourth highest peak discharge and the third largest annual volume in the 62 years of historical record. These values are 6.7% and 22.6% smaller than the maximum historical discharge and volume respectively.