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REGIONAL ANALYSES OF STREAMFLOW CHARACTERISTICS . Regionalizing Draft-Storage Relations Methods of regionalizing draft-storage re- lations are described by Riggs (1966). Appli- cations of these methods are reported by Patterson (1967) in Arkansas and Skelton (1971) in Missouri. These procedures are not true regionalizations because one or two of the variables required at each site of applica- tion are flow characteristics which must be estimated from another regional relation or from discharge information at the site. Transferring a regional draft-storage re- lation to an ungaged site may be preferable to estimating the flow characteristics at that site by other means and then defining the draft-storage characteristics from the esti- mated flow characteristics. The former meth- od seems to require less work and certainly requires less of the user of the report. . Alternatives to Regionalization The section on "Procedures for Other Flow Characteristics" described some conditions for which regionalization will not provide satisfactory results. Although it may be pos- sible to improve the regression results sub- stantially in some regions by collecting addi- tional precipitation data, making field geo- logic studies, and devising better hydrologic models, the time and cost required generally make these approaches impractical. There- fore other methods of defining flow charac- teristics at ungaged sites are needed. Some of these other methods differ from a true re- gionalization in that they require field infor- mation at each "ungaged" site. . Channel-geometry method Moore (1968) and Hedman (1970) have shown that mean annual flow is closely re- lated to the width and average depth of a selected cross section of the stream channel. Selection of the proper cross section requires some field training, but experienced men can very closely match each other's results. In a 13 recent investigation by Moore and Hedman (personal commun., 1971), the channel widths and mean depths were measured on 53 per- ennial streams in the mountain region of Colorado. These data were related to the re- spective mean flows with a standard error of about 18 percent. This derived relation can be used to estimate mean flow at any site in the region at which the channel width and average depth are obtained. Channel measurements also may be used similarly to estimate floods of selected re- currence intervals. Data at gaging stations in Nevada, California, Arizona, and Kansas have been collected and analyzed for this pur- pose. In addition, flood-peak characteristics of the 53 streams in the mountain region of Colorado have been related to channel dimen- sions. Results of these two analyses indicate the usefulness of this method on both peren- nial and ephemeral streams in the western United States. The channel geometry method has no advantage, however, over regression on basin characteristics in humid regions of moderate relief. Mean Row from monthly measurements Another method of defining mean flow of a stream requires discharge measurements near the middle of each month for 1 year (Riggs, 1969). These measured flows are related to concurrent daily mean flows at a nearby gag- ing station, using a separate relation for each month. Several trials of the method in the western United States, using gaging station records, indicate that the annual mean for 1 year may be estimated within about 10 percent from 12 monthly measurements. An estimate. of the long-term mean, based on a relation between means for that year and the corresponding long-term means at gaging stations in the vicinity, is somewhat less ac- curate. Defining mean runoff by elevation zones Riggs and Moore (1965) used streamflow records to define mean annual runoff in inch- es from 1,000-ft zones of elevation in a hydro-