Imagine the landscape between San Francisco Bay and Sacramento peppered with hundreds of inverted “islands,” dry basins isolated by levees – and below sea level, still sinking, amid a vast network of water channels.
The picture, all too real, is of California’s Delta in the 21st century.
At the April 27 annual meeting of the CSU’s Water Resources and Policies Initiatives, experts provided an overview of the Delta’s history, an update on its status, and a rundown on the key factors that will shape the outlook for its future.
Before 700,000 acres of it were “reclaimed” – diked and drained – for farming a century or so ago, the Delta was a vast ever-changing estuary of habitat diversity through which water moved slowly, taking weeks or months to make its way to the bay, said Jeff Mount, a geology professor at UC Davis and one of three Delta experts to address the WRPI meeting.
“It was self-adjusting amid constant variation,” Mount said; and it was inherently a bit salty and heavily laden with organic material with nutrients for plant growth.
“Today,” said Mount, a member of the Delta Independent Science Board, “it is basically static – managed in a way to maintain homogeneity.” Bound by a lattice of 1,100 miles of levees, the sunken basins were created as acres were drained, then farmed. The soil, without liquid to suspend it, became compacted, resulting in dry land sinking below the level of the water in channels on the other side of the levee. These cavities in the landscape, Mount said, equate to about 8,000 Rose Bowls.
The Delta still receives snow melt, experiences tidal cycles twice a day, and catches rainfall from storms. However, salts have intruded, vast amounts of organic nutrients have been carried away by winds, and the water doesn’t stick around nearly as long (half of it is diverted to satisfy the water needs of millions of Californians).
Meanwhile, sea level is rising 2 to 3 millimeters a year (and accelerating), Mount said. “And everything in an estuary is tied to sea level.”
Among other current and future challenges cited by Mount and others – representing the Nature Conservancy and the Southern California Water Committee – are changing inflows, flooding, earthquakes (which could fracture levees), and continued subsidence.
Pressures remain for further development. According to Mount, more than 180,000 new homes were proposed for areas below sea level between San Francisco and Sacramento – until plans were shelved amid the current economic recession.
A major earthquake could result in the sunken basins filling with – and in some cases trapping – brackish water, which might impair massive water supplies for months and possibly redraw the region’s map for decades.
Despite providing cataclysmic scenarios derived from data-based models, the panel offered measured optimism with caution.
Leo Winternitz, director of the Nature Conservancy’s Delta Project, cited a Chinese proverb: “Unless we change our direction, we are apt to end up where we are heading.”
(To learn about some of the Delta issues involving the CSU, see “Where Research Waters Flow.”)
– Sean Kearns