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I I I I I I I I I I I I I I I I I I I 20 period of 1974-1984 in relation to upstream gages in the basin, This is in addition to any decline attributable to a change in overall water supply in the Arkansas River Basin as indicated by the adjusted Canon City flows, The absolute decline in usable stateline flow for this period has been 48,700 acre-feet per year, Stateline flows during the last two years (1983 and 1984) have significantly exceeded the average for the eleven year period, raising the overall average for the period, The mass diagram analyses show that the significant decline in stateline usable flows starting in 1974 by far exceeds any decline which occurred in previous drought periods of the 1930's or 1950's, The decline is illustrated by comparing the period averages, the ratios of usable stateline flows to other upstream gages and the slopes of the mass curves, While the last two years of the eleven year period have been higher than average, the runoff at Canon City for these two years exceeded any previous two-year total at the Canon City gage during the study period (1908 to 1984), Based on in- spection of previous periods of high runoff, it would be expected, that this magnitude of runoff would produce the maximum usable stateline flow under the Patterson criteria. The estimated magni- tude of depletions is conservatively low because of the existence of unquantified transmountain return flows in the basin which may be removed from the river in the future, further depleting the flows, The conclusions from the mass diagram analyses are summarized below: