Don Pedro and the Managed River
Near Groveland, California
About forty miles east of Modesto, the Tuolumne River runs into a dam. The water that comes out the other side, controlled, metered, and allocated, is one of the reasons the San Joaquin Valley is what it is today.
The first Don Pedro Dam went up in nineteen twenty-three, a concrete-arch structure that gave the Modesto and Turlock Irrigation Districts their storage capacity on the Tuolumne. By the nineteen sixties, that dam was no longer adequate. The valley's agriculture had grown too large for the storage it provided, and the flood-control needs of the expanding downstream communities, including Modesto, had outgrown its design.
Construction on the New Don Pedro Dam began in nineteen sixty-seven. The river was diverted in September of nineteen sixty-eight. The embankment topped out in nineteen seventy. The project was formally dedicated on the twenty-second of May, nineteen seventy-one. The finished dam stands five hundred eighty-five feet tall, making it the tenth-highest dam in the United States at the time of its completion, and the reservoir it creates holds two million thirty thousand acre-feet of water. That is the sixth-largest artificial lake in California.
The dam is owned jointly by the Modesto Irrigation District and the Turlock Irrigation District, the same two organizations that Robert McHenry helped found in eighteen eighty-seven. Their water rights on the Tuolumne predate most of the other major water allocations in California. When the state negotiated its water compact in the mid-twentieth century, those rights, established under the Wright Act, carried substantial legal weight.
In January of nineteen ninety-seven, an atmospheric river filled Don Pedro past its operating capacity. The dam opened its floodgates for uncontrolled releases, and the Tuolumne downstream of Modesto reached a stage height of seventy-one point two one feet. Neighborhoods along Dry Creek flooded. The broader event forced more than one hundred twenty thousand people from their homes across Northern California. The river that the valley had spent a century controlling reminded the valley what it was working with.
