WSP10396

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 1/1/1964
• Author: USGS
• Title: General Effects of Drought on Water Resources on the Southwest
• Water Supply Pro - Doc Type: Report/Study

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GENERAL EFFECTS OF DROUGHT ON VVATER RESOURCES

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FIGURE 2.- Ratio of ii-year progressive average runoff to long-term mean runoff of six selected streams.

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1920

1930

1940

parison of discharge between streams is difficult to
make, For example, as read from the frequency curves,
the San Gabriel River during a third of the period
of record has had yearly runoff less than 42 percent of
its mean runoff, On the other hand, the Virgin River
has never had annual runoff as low as 42 percent of its
meau runoff and the Rio Grande has had bnt 1 year that
low. Yearly runoff, so low in relation to the average
that it never or rarely occurs on the Rio Grande or the
Virgin River, is common on the San Gabriel River and
occurs about a third of the time. These differing slopes
arc evidence of streamflow variability (p. B17).

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ANALYSIS OF REGIONAL RUNOFF
The preceding discussion and accompanying illus-
trations indicate the effect of drought on six selected
streams. But what happened on the thousands oT other
streams in the Southwest, or even at other points on
the six streams! Fewer than a hundred records in
the entire Southwest are oT suitable length and quality
Tor similar 'analysis. If these were presented in tables,
diagrams, and text, as was done for the six records, the
additional information would detail only the particu-
lar streams included. Little would be added to knowl-
edge about runoff in ungaged streams or about broad
trends unless general conclusions could be drawn about