For more than 60 years, California officials and experts have discussed expanding the Sacramento River bypass and levee system.

最初的系统是针对1907年和1909年两次洪水而设计的，于1955年完成，并于当年对其迄今为止最大的洪水进行了测试。另外三洪洪水，包括1986年有记录的最大洪水，表明该系统应内置更多的洪水能力和保护。

在2020年夏季，承包商在第一个扩大该能力的项目上打破了地面，即低埃尔克霍恩盆地堤坝挫折（LEBLS）项目。加利福尼亚水资源部正在领导这项1.03亿美元项目的设计，建设和许可，该项目将扩大萨克拉曼多旁路和Yolo旁路的东侧。

In the process, DWR is setting back five miles of the east levee of the Yolo Bypass and all two miles of the north levee of the Sacramento Bypass. The two levees form an “L” shape that will be set back about 1,500 ft. DWR is working closely with the Sacramento Area Flood Control Agency (SAFCA), which received a $25-million contract for the interior drainage and pump station work.

“Something was identified as a problem in 1955, and it’s taken a long time and a few more flood events to let the engineers know that the ’55 event wasn’t the exception, it was the norm,” says Dan Tibbitts, principal engineer and project manager with SAFCA.

The LEBLS project is the first one to come out of the state-legislated Central Valley Flood Protection Plan completed in 2012, Tibbitts says. The plan aims to increase the bypass system’s capacity while strengthening the area’s ecosystem and climate resiliency. DWR is also working with federal fish and wildlife agencies and the local reclamation district.

This project will double the capacity of the Sacramento Bypass, add about 60,000 cu ft per second of capacity to the Yolo Bypass and add hundreds of acres to the floodplain in the bypasses, says David Pesavento, DWR senior water resource engineer and project manager. Several improvements have strengthened the flood control system around Sacramento, but LEBLS is the first project to add more floodwater capacity.

该项目广泛：该团队必须在700英亩的土地上移动超过500万立方英尺。Pesavento说，今年早些时候，该团队完成了800英尺的堤防，新的泵站和新盆地和涵洞的路堤。

General contractor Forgen LLC was excited to join in, says project director Jared Williams. “We saw this job as a unique earthwork job, and we do a lot of wetlands work.”

Fed by the Klamath Mountains to the north, the Sacramento is a “perched” river, with natural levees that set it higher than the valley floor. In high-water events, the river naturally rises and overflows its banks into the floodplains on either side.

The region’s earliest settlers built structures to control this cycle, and now the flows are shunted into a system of bypasses designed to capture much of the Sacramento River’s water.

在萨克拉曼多附近，这条河的主要叉子的容量为美国河以北的每秒107,000立方英尺，而美国河的容量为180,000 CFP。然而，只有110,000个CFP可以从大萨克拉曼多地区出现，继续前往旧金山湾。

The LEBLS project’s biggest engineering challenge relates to soil conditions. Much of the area is full of “fat clay” that wouldn’t ordinarily meet the Army Corps of Engineers’ standards for levees, says Pesavento. But trucking in millions of cubic yards of more suitable soil would have driven up costs and exceeded the project’s emissions standards.

结果，Lebls团队正在从当前和未来的建筑堤防之间挖掘土壤。建造新堤坝后，团队将拆除大部分原始堤防，并使用该材料恢复挖出空间。粘土根据其水分含量提供不同的建筑挑战。它在该地区的冬季降雨期间膨胀，然后随着干燥并产生干燥裂缝而收缩，深7英尺。

佩萨文托说：“有了太多的水，粘土变得非常滑，几乎就像建模粘土一样。”“如果太干，它会变得非常困难，边缘锯齿状，您将无法获得所需的压实。”

Forgen适应挑战,威廉姆斯说。When the company bid on the job last summer, its team expected to build with already water-saturated clay. But the region’s current dry conditions required a moisture-adding approach instead.

“We started with water trucks, pivoted to sprinklers, then to outright flooding,” Williams says. Drainage ditches run for miles, fed by wells locally obtained by DWR. ”We learned when something’s different than we expect, let’s completely scrap our estimate, forget what we thought we knew and just build it the way we think we can build it.”

工程师设计了新的堤坝来容纳这种粘土。Pesavento说，现年100年历史的当前堤防具有更常见的2比1或3-1的侧面坡度，已经发生了多次失败（但没有破坏），部分斜坡滑动或跌落。。新的堤防更宽且更平坦：皇冠上有28英尺的宽度，有4比1的侧面斜坡。堤防完成后，陆军工程兵团将扩大1916年完成的萨克拉曼多堰，以使洪水期间更多的水进入旁路。

Lebls项目是DWR的一个多效项目，可以平衡对基础设施和防洪的需求。
Photo by Florence Low, courtesy California Dept. of Water Resources

水和野生动植物

The levee’s designers also had to consider erosion control, since the region’s southwesterly winds can cause wave wash against the levee. Placing rocks to protect the levee sides wouldn’t do because new vegetation would cause environmental and operational problems. Instead, the team is using tied-concrete-block mats to protect the levee—little concrete blocks placed and cast into a synthetic material to hold them all in place, Pesavento says.

佩萨文托说：“一旦我们放了堤坝，我们就会放置那些垫子，然后在堤防上种植多年生的本地草。”该团队去年开始在测试地块中的此类垫子上种植草，以找到培养这种草覆盖的最佳方法，这将稳定堤坝的顶部并扼杀诸如蓟等入侵物种。

他说，盆地是迁移鸟类（例如斯威森的鹰）的流行区域。Yolo旁路本身包含在太平洋飞行道中，该飞行为迁移鸟类提供了中途停留点。DWR还在研究鱼类如何在河流的洪泛区和主茎上蓬勃发展。旧堤防的残留物将为巨大的吊蛇等动物创造隐藏和安息的空间。

Designing and building the LEBLS project required years of planning and coordination among competing interests, Pesavento said. The floodplain and river not only must handle high-water events, but they also must support native plants and wildlife as well as recreational uses and water supply storage. To ensure all interests are considered and protected, DWR is partnering with the Yocha Dehe Wintun Nation, a local Native American tribe, as well as agencies involved in flood protection, conservation and the environment.

该州和其他机构还计划将上埃尔克霍恩盆地和两英里长的弗里蒙特堰以及向南的堤坝撤回堤坝和旁路。这些扩展能力的项目仍处于研究阶段，将包括联邦和州参新利18备用网址与的组合以及DWR和地方实体，例如开新利18备用垦区和SAFCA。