New campaign of levee work planned along Sacramento River

A massive new round of levee improvements is ahead for Sacramento over the next decade, this time focusing primarily on the Sacramento River south of downtown.

The work is estimated to cost nearly $1.5 billion and will be concentrated on levees adjoining Land Park, Greenhaven, the Pocket and Little Pocket neighborhoods. The proposed work includes building deeper seepage walls inside the levees and more protection from erosion.

Another project involves nearly doubling the width of the Sacramento Bypass, a structure across from Natomas that diverts Sacramento River flood flows into the Yolo Bypass through a weir. The project includes building a second weir to feed the wider bypass.

The proposal comes just as Sacramento’s Natomas Basin is emerging from seven years of flood-safety restrictions that stymied construction and imposed steep flood-insurance rates on thousands of property owners. The building restrictions are poised to be lifted this summer, while the insurance requirement will continue.

Sacramento officials hope to spare neighborhoods south of downtown from the same fate by getting started now on major levee upgrades.

The U.S. Army Corps of Engineers and Sacramento Area Flood Control Agency unveiled the package of projects recently and are planning a series of public meetings in April.

The work is triggered by several recent changes in flood-control policy.

First is a long-running project by the Federal Emergency Management Agency to assess flood risk more accurately. Known as a “remapping,” it involves adopting new flood-risk maps designed to account for new research by the Army Corps and others on levee stability, and more accurately assessing risks to life and property behind levees.

The Sacramento River levees are at risk of being downgraded as part of the remapping process, potentially triggering a flood-insurance requirement for tens of thousands of Sacramento property owners in Land Park, the Pocket and other neighborhoods. A similar downgrade has afflicted Sacramento’s Natomas region since December 2008. This resulted in a de facto building moratorium that is expected to be lifted later this year as levee upgrades worth $1 billion continue in the region.

“We’re trying to be actively moving forward so that FEMA will not start the remapping process,” said SAFCA executive director Rick Johnson. “That’s really what our goal is there.”

A second factor is state legislation approved several years ago that requires all urban areas in California to meet a 200-year level of flood protection. That means the ability to withstand a flood with a half-percent chance of striking in any given year. This is double FEMA’s 100-year standard to avoid a flood-insurance requirement. Sacramento is required to meet the 200-year standard.

Officials emphasized the levees in question are not considered unsafe. They simply do not meet newer safety standards.

“Through the corps’ review and SAFCA’s own review of these levee systems, we realized they’re just not meeting design standards,” said Pete Ghelfi, director of engineering at SAFCA. “From a public safety standpoint, we want to move as quickly as possible to get this done.”

That means SAFCA will borrow from its playbook in Natomas. The normal route to construction for a flood-control project of this size is to wait for authorization and funding from Congress. Then a local agency such as SAFCA offers up its share of the funding, and construction begins. That process can take years, if not decades.

Instead, SAFCA will spend about $160 million to start building the most critical levee segments – with the blessing of the Corps of Engineers – and be reimbursed later by the federal government. It hopes to start construction in 2017.

Improvements to meet the new standards could require wider and taller levees on some portions of the Sacramento River in some of the most heavily urbanized sections of the city. But there isn’t room for bigger levees in the Pocket and parts of Land Park, because development was allowed to occur too close to those levees decades ago. Enlarging the levees would require buying millions of dollars in real estate and relocating hundreds of families and businesses.

The proposed project is designed to avoid that disruption by enlarging the Sacramento Bypass. The bypass, north of the American River confluence and across the Sacramento River from Natomas, was built a century ago to divert floodwaters away from Sacramento.

When the river is flooding, gates in the Sacramento Weir are opened manually, diverting a portion of the river’s flow into the Sacramento Bypass, which sends that water into the Yolo Bypass. This reduces flood depths downstream for the city of Sacramento.

By nearly doubling the width of the bypass and adding a second weir to feed it, the proposed project will slash flood depths even further, reducing the need to raise and widen levees downstream.

About 9 miles of levee along the Sacramento River must be upgraded with new seepage walls, which consist of an impervious material poured into deep trenches cut within the levee. For Pocket-area residents, this work will seem like déjà vu. The neighborhood has seen numerous seepage wall projects over the past several decades. But safety standards now require deeper walls. In some cases, the new seepage walls will serve as a levee strengthening tool, designed to anchor the levees more solidly to deeper soil layers.

In North Sacramento, several miles of Arcade Creek and the Natomas East Main Drainage Canal would see similar seepage control work under the plan. Some of these levees also need to be raised to contain deeper floodwaters.

About 800 mature trees may have to be removed for all this work, representing about 10 percent of some 8,000 trees growing on the affected levees.

The plan includes extensive work to prevent erosion along the Sacramento River and the American River. This would involve reshaping the levee surface and placing large rocks on the levee slope. New planting berms are planned in some locations to disguise the rock.

This story was originally published March 29, 2015 at 5:13 PM with the headline "New campaign of levee work planned along Sacramento River."