What are they doing to the levees?

Building the deep cutoff wall

seepage

There has been a lot of work on the levees in Sutter County over the past several years, including $28.5 million in emergency work on the west bank of the Feather River at Yuba City. But what are they doing?

Already, the Sutter Butte Flood Control Agency has spent $300 million on close to 37 miles of levee work south of Yuba City to Starr Bend and north of Yuba City into southern Butte County. Now they are doing the same at Yuba City, although the levee at Yuba City was “fixed” after the 1997 flood.

Except it wasn’t, as we found out in the high water episode of February, when we saw seepage, boils, and sink holes develop on the levee side, even though water levels did not get as high on the levee as in 1955, 1986, or 1997. Levees rarely are overtopped by flood waters. They typically fail as the result of through seepage or under seepage.

So what’s being done about the levees? The Sutter Butte Flood Control Agency, a model local government agency created just to fix our levee system and provide relief from restrictive flood map designations and expensive flood insurance requirements, has been installing a deep cut off wall down the middle of the levee to block under seepage and through seepage since 2013. (See picture above).

The slurry wall consists of bentonite clay from Utah and Wyoming, soil, and water mixed to the thickness of peanut butter. A 36-inch wide ditch is excavated down the middle of the levee as deep as 120 feet in some locations. After the slurry is placed into the cavity, and settles for about three weeks, it will provide an impermeable seal between the river and the people, homes, and businesses on the land side.

During the Feather River high water of 2017, all of the work on the west bank of the Feather performed by SBFCA north of Yuba City and south of Yuba City stopped historic seepage. When the emergency work is completed this fall at Yuba City, we will have some of the strongest levees in the nation, and the impermeable wall will stretch from the Thermalito Afterbay to south of Starr Bend.