海平面上升以及干旱和地震，威胁着保护萨克拉曼多山华金河三角洲的堤防，该堤防为2500万加州人提供了淡水。But the state’s solution isn’t to build higher but lower—150 ft below the earth.
加利福尼亚州的水资源部计划在三角洲下方挖掘两条重力喂养的40英尺二木隧道，以将淡水从萨克拉曼多河转移到南部三角洲南部的联邦泵站。这项耗资157亿美元的三角洲隧道项目于1960年代首次提议是外围运河，以三角洲的速度滑行，于7月下旬获得了该州的环境认证。
“We’re engineering for a 200-year storm event in the delta, plus another 18 inches for sea-level rise,” says John Andrew, DWR’s assistant deputy director. “We’re figuring 55 inches in sea-level rise at the Golden Gate in the next 100 years.” With that amount of sea-level rise, saltwater would be pushed into the delta.
To avoid saltwater intrusion and reduce reliance on the delta’s 1,100-mile levee system, the proposed California WaterFix project would draw water from the Sacramento River in the north of the delta. The system could divert up to 9,000 cu ft of water per second into about 43 miles of tunnels to a new pumping plant on the delta’s southern edge.
挖掘巨大的隧道,承包商send tunnel-boring machines down deep shafts, dug through the delta’s peat layers and into dense deposits of silts, sands and clay. Engineers adopted a twin-tunnel system, since constructing a single tunnel capable of conveying up to 9,000 cfs would require a machine larger than any currently used—60 ft or more in diameter.
此外，隧道建设将需要在三角洲的基础设施中进行支持，包括新的道路和电力线，驳船通往三角洲群岛以及瓦斯和水井的去除或搬迁。DWR估计为该项目配备12到15个月，四年来完成设计，大约13年进行建设。南加州大都会水域的工程经理约翰·贝纳尔斯基（John Bednarski）表示，该州预计将于今年秋天将RFP派出隧道设计师和泵设计师，并开始选择一家公司来担任工程设计经理。
WEST COAST在全球海平面上升的每一脚都因在南极西部的冰上流失而造成的每一脚，海洋将在加利福尼亚海岸上升约1.25英尺。
Lawsuits by fishing and environmental groups, however, threaten the project’s timeline. The Natural Resources Defense Council, Defenders of Wildlife, Bay Institute and Golden Gate Salmon Association say the proposed tunnel system would shunt high-quality Sacramento River water to Southern California customers and Central Valley farmers before it ever reaches the delta, endangering the region’s fish and wildlife. Water officials contend that the proposed WaterFix, along with the current system, would protect the fragile ecosystem and allows the DWR to gulp more water during large storms and sip less during droughts.
“Right now, we rely heavily on those delta islands staying intact and levees holding. But we can’t depend only on levees,” DWR’s Andrew says. “We expect not only rising seas. We expect extreme floods.”
Along the coast, San Francisco grapples with the same tidal forces. The city has put a $350-million bond issue on the November 2018 ballot to start improving its decaying 100-year-old seawall. Upgrading the three-mile, waterfront-supporting stretch would take decades and cost about $5 billion, says Steven Reel, project manager at the Port of San Francisco. And like the delta levees, the wall’s crumbling infrastructure and weak, muddy foundation leave it vulnerable to an earthquake.
“我们需要以整体方式研究这些项目。新利18备用网址这项计划工作将在未来50年内研究地震风险和海平面升级计划。” Reel说。
