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Washington 25, D. C.


The population of San Diego in 1940 was slightly over 200,000, and at that time it was predicted that the growth of population would not exceed 350,000 by the year 1960.

When the United States was drawn into the war large military organizations, training camps, and industrial plants were established in and around the city. The consequent influx of military personnel, defense workers, and their families shot the population up to 440,000 early in the year 1943. This extraordinary increase placed a great strain on many community facilities. The water supply was no exception.

The water supply of the city of San Diego is now obtained from three principal drainage basins located in the coastal mount ns. The crests of these mountains are relatively near the ocean and the streams are short and of erratic flows. Because of the seasonal character of the rainfall and variable nature of the run-off, the city has necessarily constructed, for water-supply purposes, a system of reservoirs to catch and hold the large periodic floods which occur approximately at intervals of 10 years.

The annual rainfall averages about 10 inches along the coast and is four to five times greater near the crest of the mountain range. Practically all of the precipitation occurs during the months of December to April, inclusive. The rainfall varies from year to year, and the volume of the annual run-off is very erratic, ranging from extremes of only 2.6 to as much as 580.8 percent of the mean for the 60-year period of record, 1883 to 1943.

In the light of past records of run-off from the local streams, there is cause for anxiety regarding the ability of the supply as developed by present works to meet the demand which is not being made upon it. Fortunately, good run-off filled the reservoirs in the winters 1940-41, 1941-42, and 1942–43. However, it was predicted in 1943 that the present stored water would be nearly depleted by the year 1946, should there be a recurrence of a dry cycle similar to that which began in the year 1897 and continued through the year 1904. Such a drought may recur at any time.

In June 1944 it was thought that the city of San Diego had sufficient water in storage to supply its users through the year 1947. During the subsequent 3 months, however, the volume of use increased to such an extent that the supply may be depleted by July 1917.

The meter records of water supplied by the city of San Diego disclose that the various military establishments, housing, and aircraft plants, during the years 1940, 1941, 1942, and 1943 used 10.9, 17.5, 28.4, and 40.3 percent, respectively, of the total quantities of water delivered to the city.

Increased storage facilities are contemplated by the city but even if completed in the near future no assumption of an augmented firm supply can be made-for if a cycle of dry years, similar to the driest cycle of record, should recur there would be little run-off to store. Because of wide variations from year to year in stream run-off, a safe yield from local sources must be predicated on hold-over storage with which to enter the dry cycles. Local storage developments might not provide additional water likely to be needed for this purpose.

It seems evident, therefore, that a firm supplement to the water supply that is obtainable from local sources is now required. Only with a fortunate continuation of wet winters can the greatly expanded needs of the city otherwise be met, and it would be foolhardly to rely on a continuation of the favorable conditions of the past 3 years, in view of the well-established erratic character of the precipitation and run-off in San Diego County. A firm supplemental water supply can be obtained for the city only from the Colorado River, and it has been long anticipated that eventually it would be obtained from that source.


OCTOBER 10, 1944.


Reservoir capacities and storage

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The storage shown in the above tabulation is subject to outstanding commitments to the California Water & Telephone Co., La Mesa, Lemon Grove, and Spring Valley Irrigation District, Santa Fe Irrigation District, San Dieguito Irrigation District, Del Mar Water, Light & Power Co., and a number of minor water users. Run-off at city reservoirs

Acre-feet 60-year mean, 1883 to 1943.

139, 103 7-year mean, 1936 to 1945.

219, 924 7-year mean, 1897 to 1904.

14, 914 3-year mean, 1897 to 1900

5, 837

Safe yield of présent sources before and after San Vicente three-fourths filled

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1 Estimated
Increase 1939 to 1944, 9,296.1 million gallons, or 28,529 acre-feet, or 122.3 percent.

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Total use, evaporation, and seepage from all reservoirs

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Maximum demands and average use by city and military in million gallons a day

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It is indicated that with run-off for the next 3 years the same as for the period 1897–1900, the city's San Diego River System will be empty by May 1, 1947, at which time there will be less than 6 months' supply in the Lorena, Barrett, Otay Reservoir system. To provide a working margin of safety, there should be at least 6 months' water supply in the San Diego River System when the first delivery of Colorado River water is received.

FRFD D. PYLE, Hydraulic Engineer.



Washington, October 21, 1944.

The White House. SIR: In response to your letter of October 3, 1944, your committee on methods of financing the San Diego water supply project was organized with the following members:

William E. Warne, assistant commissioner, Bureau of Reclamation, United States Department of the Interior, chairman,

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