California Policymakers to Rethink Dams

Nine people died in the floods that rampaged through the state at the start of the year. Some 24,000 homes were destroyed.

"Setback levees and bypasses, especially on the San Joaquin River, have got to be looked at very carefully," says Walter Yep, the Army Corps of Engineers chief planner for California, Colorado, Nevada, and Utah.

Over the last 80 years, the state has set up vast mechanical engineering complexes throughout the eastern and northern parts of the state to make the rivers spread over a wide area. The plan was aimed at preventing flash floods, creating new farmland in the south, and supplying water to the cities in the west.

Flash floods used to threaten the state capital of Sacramento once every three years. A system of dams and levees on the San Joaquin River has prevented these minor floods while delivering new water for farming to the Yolo bypass to the west of the city.

Not far from Sacramento, in the foothills of the Sierra Nevada mountains, a series of dams was built to trap the winter rains and channel the water into the southern farmlands of California's Central Valley. And dams were built to the north of Sacramento, on the Feather River, to bring water to Yuba City and the agricultural land to the south. The Stanislaus and Tolumne rivers were dammed to the southwest of Sacramento to provide water to farmland near Modesto.

Creation of the farmland brought new farmers. Modesto's population rose from 17,389 people in 1950 to 181,800 in 1996. The population of nearby Manteca, which numbered 13,845 in 1970, is now nearly three times that size. And Stockton, which had 107,000 residents in 1970, grew to 233,600 in 1996.

The water control systems were not designed to prevent so-called once-in-a-century floods. But as unusually warm rains melted the snowpack, creating more run-off than usual, seven such floods ravaged the area in the last 40 years.

As the New Melones Dam on the Stanislaus River and the New Don Pedro on the Tuolumne River filled on Jan. 1, a thousand families were evacuated from Modesto. The Tuolumne River swelled to a 21-meter level, the highest in half-a-century and more than four meters above flood level.

At the same time, 21,735 cubic meters of water per second rushed into the Shasta reservoir on the Sacramento River. The reservoir filled to 97 percent of capacity within days.

"They just had to let the water go; they had no choice," says Bill Mork, the state Department of Water Resources' meteorologist who alerted flood managers of major problems shortly after Christmas.

The result was a disaster, with floods in almost all of the mobile-home parks along the banks of the Tuolumne.

Scenes like these, which are familiar in many parts of the world, inspired the new book, "Silenced Rivers: The Ecology and Politics of Large Dams."

"By misleading people into thinking that they can control huge floods, dams encourage settlement on floodplains, turning damaging floods into devastating ones," says Patrick McCully, U.S.-based river activist and author of the new book.

McCully and other critics argue that dams built to deliver water, electricity, and wealth have attracted migrants to settle in floodplains, making them vulnerable to sudden disasters. Other dams have been built in densely populated areas to help tame unpredictable rivers. Although they may work in the short term, years of neglected problems have culminated in huge disasters.

McCully's book recalls some of the consequences of dam failures over the past few decades. In China, an estimated 230,000 people were killed when the Banqiao and Shimantan dams malfunctioned on a tributary of the lower Yangtze in Hunan province in August 1975. When the Vaiont Dam in the Italian Alps failed in 1963, some 2,600 people were killed. And about 2,000 people perished when the Macchu II Dam in India failed in 1979.