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maximum-annual discharge (average of the mean-daily flow for the highest day of the year) for the Gunnison River declined about 47$ between the early development and post-Aspinall periods (Table 1). It declined about 37$ in the Colorado River (Cisco gage) between the same two periods (Table 1). Mean- monthly flows have also changed over the three development periods (Figure 7; Tables A5 and A6). In general, spring and early summer flows have declined, and fall and winter flows have increased. Mean-monthly flows in May and June, the primary runoff months, have declined 43 and 47$ (respectively) in the Gunnison River (Table AS), and 31 and 37$ in the Colorado River (Table A6). Flow changes calculated by comparing actual Gunnison River streamflow with the estimated flow that would have occurred without any development were comparable to those estimated for the runoff period using the three development periods (Table 2; Table A7). However, estimated changes for the remainder of the year differed substantially. This is undoubtedly due in large part to the irrigation diversions that were already in place when stream gaging began. The water diverted for irrigation would be a small portion of the available water during runoff, but would be a large portion of streamflow during summer months. Thus the 'early development' streamflows were already less than natural flows. The effect of the Aspinall Unit on runoff was estimated by comparing the change in streamflow from the middle-development period to the post-Aspinall period. Mean-monthly streamflow declined about 1.4~ in April, 25.1 in May, and 32.2 in June (Table 3). streamflow during the remainder of the year has increased, particularly during the winter when average flows are more than 100$ greater than pre-Aspinall flows (Table AS). Gunnison River mean-monthly flows have declined an average of 1,864 cfs in May and 2,326 cfs in June 19