Prado Dam Remarks Bring a Flood of Dissent

Clearly, I put my foot in it when I tested the water here with Allan A. Schoenherr’s opinion that enlarging Prado Dam and its reservoir was simply a Corps of Engineers’ billion-dollar boondoggle.

Schoenherr, a professor of zoology and environmental science at Fullerton College, believes that the probability of a 100-year or 200-year devastating flood of the Santa Ana River is extremely remote.

“The probability of tossing heads on a coin does not change, no matter how many times you toss it. Similarly, the probability of such a flood does not change as time passes. The existing Prado Dam was built with that knowledge at hand, and it is absurd to assume we must make it higher a mere 40 years later,” Schoenherr wrote.

Letters of protest followed. Among them was one from C. R. Nelson, Orange County’s director of public works, who said that Schoenherr is partially correct about the probability of a serious flood. However, Nelson points out that time has passed since the dam was constructed.

“The magnitude of such a flood and the damage potential are, in fact, changing as more development occurs on the tributary watershed. For example, it is incontestable that for a given amount of rainfall, the runoff from a proposed automobile sales mall in the Corona area will be significantly greater than the runoff from the same piece of property as historically used for agricultural purposes,” Nelson wrote.

He says that if Schoenherr, he and I were writing about this problem during the mid-1930s, it would seem absurd to assume that within 40 years agriculture would not be the principal business of Riverside and San Bernardino. Accordingly, he says, it would also have seemed absurd in 1939 to increase the size of Prado Reservoir for the runoff of an almost totally urban development between Pomona and Corona.

Historically, the voters of Orange County in 1929 decided against a bond issue supported by property taxes to protect the farms and towns of Orange County from the extremely remote probability of flooding.

The flood of 1938--when 45 lives were lost in a sparsely populated rural area--caused the federal government to construct the existing dam and reservoir at Prado at a cost of about $10 million.

Nelson observed that Prado has served very well over the years but that times have changed. The reservoir and dam do not have sufficient capacity for the runoff from future upstream urban development, he said.

“Further, the area that would be flooded is no longer an area of orchards and truck farms. Approximately one million people make their homes in the potential overflow area. After a few hundred of these residents were flooded March 1, 1983, from a locally intense storm over the Fountain Valley and Huntington Beach area, our explanation that the local flood control system was not designed to accommodate the ‘extremely remote probability’ of such an event was simply unacceptable to affected citizens.”

Nelson firmly believes that very few responsible officials want to see the lives of 3,000 Orange County residents risked in order to save the money that it would cost to improve the Santa Ana River. He says that the $l-billion cost for the Santa Ana River Main Stem Project is justified solely by the benefits, which he estimated at about $11 billion in damages that would be avoided.

Another letter writer, George Osborne, executive director of the Santa Ana River Flood Protection Agency, was more pungent and personal, but said much the same thing as Nelson.

Jean Powell of Huntington Beach believed that I was “heartless” to have presented a dissenting view on the Prado project. Her lay opinion was similar to that of the experts.

“Forty years ago, when Prado Dam was built, there was a far greater chance that the intervening ground would absorb much of the floodwater. No one guessed then how much that ground would be covered over with concrete and asphalt, or how many people would move into the vulnerable areas. Please, please, write another column saying how much you hope, for our sakes, that the work will start soon,” she wrote.

OK, for your sakes, get to work, Engineers! Yes, the topography has changed with time’s passage. Unfortunately, the rich agricultural flood plain is now growing houses that certainly won’t benefit from a deluge, whatever the probabilities.