Relations of runoff to altitude may be defined for a hydrologically homogeneous region by using a limited number of streamflow records. Mean runoff from ungaged basins in this same region can then be computed on the basis of this derived relation. When these relations of runoff to altitude are applied to small areas, the runoff may be different from that indicated by the relation, because oflocal differences in geology, precipitation, vegetation, land slopes, and land use. Two methods are described for adjusting the relations for the effects of these variations; one based on a streamflow measurement at miscellaneous sites which is applicable to perennial streams, the other on measurement of two channel parameters which is applicable to either perennial or ephemeral streams.

The mean annual runoff and peak discharges having selected recurrence intervals have been related to the width and average depth of cross sections between channel and point bars for 53 gaged sites on perennial streams in the mountain region of Colorado. These relations and measures of channel dimensions can be used to estimate streamflow characteristics for ungaged streams in the Colorado mountain region. The standard error of estimate is 18.3 percent for the relation with mean annual runoff, and ranges from about 30 percent to 45 percent for the relations with peak discharges having recurrence intervals of 2, 5, 10, 25, and 50 years. The standard error of estimate generally increased with the recurrence interval for peak discharges.

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