With the first drenching rainstorm under Northern California’s belt, focus will now shift from wildfires to floods. 

“We have to keep in our minds that even when it’s fire season, flood is not far behind,” said Joe Thomas, of KSN, Inc., who is conducting flood risk deduction feasibility studies along the Sacramento River, in the communities of Colusa, Grimes, and Princeton.  

While rain is a welcomed sight after years of drought and the deadliest wildfires in California’s history, the question on the minds of people living along the Sacramento River is one they have struggled with years – what is the risk of a catastrophic flood? 

“It’s going to happen,” said Chris Torres, a local farmer and president of the Colusa County Farm Bureau, at a community meeting in Princeton. “There is going to be a catastrophic flood and people are going to be impacted.” 

Just as with thousands of communities participating in the National Flood Insurance Program, the Federal Emergency Management Agency’s flood hazard maps for Colusa, Grimes, and Princeton will eventually be updated. 

Although it could still be years away, the new FEMA maps will ultimately be used to determine flood insurance rates, KSN officials said. 

Meanwhile, KSN’s flood reduction studies, which build upon Regional Flood Management Planning efforts, should eventually identify a preferred solution for each community to reduce their flood risk, while providing opportunities for multi-benefit and habitat enhancement.

Currently, the potential for flooding, even on high ground where most of the population lives, stems from both through-and-under-seepages in the levees, which were built from gravely and sandy soils by the early settlers, Thomas said. 

With through-seepages, high river levels dislocate predominantly sandy soil, which causes sloughing and failure on the landside of the levee slope. With under-seepages, high water puts pressure on the sandy and gravely soil beneath the clay blanket.

“Both can cause catastrophic failure on the landside of the levee,” Thomas said. 

Repairing the levee, if that is found to be one of the alternatives gleaned from the study, would be an expensive undertaking, costing from $5 million to $7 million per mile of levee, he said. 

The Sacramento River West Side Levee District’s just completed a river seepage repair project, a $7.3 million effort to reduce flood risk in a historically leaky segment of the Sacramento River West Levee near Knights Landing. The project, the largest-ever led by the district, involved building a 9,000 foot-long berm along the levee toe that will drain seepage away from the levee during high water events. 

The California Department of Water Resources funded 85 percent of that project through a grant. The rest is being funded by local property assessments.

Residents in Colusa and Princeton, however, believe their greatest risk for flood stems from decades of reforestation by environmentalists, which has lead to shallower and plugged river channels, and could result in flood waters going into areas that hasn’t historically flooded.  

“The river needs to be cleaned out to the standards of the 1930s,” Torres suggested as a potential solution. 

Residents also said more work should be done to enhance drainage, so that water within the communities has a place to go during high water events. 

KSN is expected to develop three alternatives to reduce flood risks in Colusa, Grimes, and Princeton, which will be available for public review by May 2019. 

Their aim then is to come back and talk to the public to discuss the recommendations before approaching the government to help finance flood risk reductions, such as costly levee repairs. 

County officials said it is important for residents of these communities to be involved in this process, as they will ultimately have to fund some of the costs. 

While Princeton had a large turnout at the community meeting on Nov. 15, at the high school, only a couple of people attended the meeting in Colusa two days earlier. 

“We need to have a plan,” said Supervisor Denise Carter. “It’s not just ‘let’s go fix the levee.’ We have to do what we have to do.” 

Carter said any solution to reduce flood risk would be a “big fix” but without 100-year flood protections in place before remapping, flood insurance rates for most residents would become unaffordable, and the city/county would be unable to issue building permits for any construction within a recognized flood zone. 

“These communities need 100-year flood protection,” she said. 

Kim Floyd, KSN public outreach coordinator, said it is important for residents to understand that a “100-year storm” is defined as a 1 percent chance of a flood occurring in any given year, not the chance that a flood will occur every 100 years. 

“The 100-year flood is an attempt to simplify the definition of a storm or flood that statistically has a 1-in-100 chance of happening over a 1-year period,” she said. “In other words, you can have several 100-year storm events in the same year, the same month, or even the same week.” ■