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Perspectives in Engineering Geology: Impact of the Great 1938 Previous HitFloodNext Hit in Southern California

R. J. Shlemon
P.O. Box 3066, Newport Beach, CA, [email protected]

The 1938 floods in southern California devastated much of Los Angeles, Orange, and western Riverside and San Bernardino counties. Debris and mudflows destroyed substantial portions of many foothill communities. Flooding along the Santa Ana River caused the death of ~200 people, inundated much of Anaheim, Garden Grove, Fountain Valley, and Huntington Beach, and destroyed almost every bridge from the foothills to the ocean. Also severely damaged and eventually abandoned were many sections of the Pacific Electric (red cars) system. Discharge along upper reaches of the Santa Ana River (San Bernardino County) was ~100,000 cfs with an estimated return frequency of about 20 years. In comparison, the “Noaic,” 1862 Previous HitfloodNext Hit was three times greater (~300,000 cfs) with an estimated 200-yr recurrence. The 1938 Previous HitfloodNext Hit led to passage of the Previous HitFloodNext Hit Control Act of 1941, which ultimately gave rise to canalization of the Los Angeles, Santa Ana, San Gabriel, and other drainage in southern California; to building of foothill debris basins; and ultimately to construction of the Prado Dam across the Santa Ana River at Corona and the more recent, upstream Seven Oaks Dam, ironically astride the active Chino and San Andreas faults, respectively.

Many 1938 Previous HitfloodTop scenes in Los Angeles and Orange counties were fortunately captured by a “hobbyist” on 8-mm imagery, and these will be viewed via a digitally enhanced DVD.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009