WSP00007

• File Number: 8281.400
• Description: Colorado River Studies and Investigations -- Colorado River Depletion Projections
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/1/1969
• Title: Past Depletions
• Water Supply Pro - Doc Type: Report/Study

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PAST DEPLETIONS

Historical streamflows are the basic flows from which ~he water supply

available to the Upper Basin was derived. Historical flows are the runoff

as it actually occurred under past conditions of upstream uses. In-basin

irrigation, domestic use, trans-basin exports, and evaporation from

reservoirs in the basin are the only appreciable upstream depletions to

the natural runoff in the upper basin.

We are interested in (1) estimating the past depletions, (2) estimating

the natural or virgin runoff, and (3) determining the 1968 modified .flows.

The 1968 modified flows represent the streamflows which could be expected

with a recurrence of a runoff period similar to 1906-1968 at the 1968 level

of upstream development.

Past depletions were estimated by the procedure used for determining

virgin flow. Table I, on the following page, is the original tabulation of

virgin flow prepared for the Colorado River Storage Project Planning Report,

1950.

Column 1 of this tabulation is the annual historical flows.

Column 2 presents the .estimated irrigated acreage for each year during

the period of study. Curve I presents estimated acreages irrigated each

year within the upper basin during the 1906-1947 period, These acreages

were estimated after consideration of all available data including the

Bureau of Reclamation land classification survey of the basin (1932-1938),

Bureau of Census data, and data assembled by the Engineering Advisory

Committee.

Column 3 gives an adjustment factor necessary to reflect the annual

variation from the nonnal water supply available at sites of use. In