Q&A with Jeffrey Twitchell on Reducing Flood Risks for California’s Delta Legacy Communities While Improving Water Conveyance Reliability Through the Delta

By Quinn Fenger and Jeff Twitchell

Jeff Twitchell has spent more than four decades working on water resources and environmental projects across California. A professional engineer and senior consultant at GEI Consultants, he understands the Central Valley’s levees and waterways like few others. At the 2025 Floodplain Management Association (FMA) conference he’s presenting “Reducing Flood Risks to Disadvantaged Delta Legacy Communities in the Lower Sacramento River Corridor.” His session focuses on the small agricultural towns along the Sacramento River—communities like Clarksburg, Hood, Courtland, Locke, Walnut Grove, Ryde, Isleton, and Rio Vista. These communities are situated behind aging levees on land that was once tidal marsh. Many residents are low-income farmers who can’t afford high insurance premiums, even though a levee failure could inundate homes by ten feet or more. Twitchell sat down to talk about his presentation at FMA with a focus on why these communities matter, the challenges they face, and how a Lower Sacramento River Corridor Management Plan could be of significant value to them.

Q: First, why should FMA attendees care about your presentation?

A: We just want to bring greater awareness to this section of levees in the Lower Sac–Delta North Region of the Central Valley Flood Protection Plan (CVFPP) 2027 Update. It’s probably the largest area in the Delta with state and federally authorized levees that need upgrades. A lot of the CVFPP focuses on urban areas or the Yolo Bypass, and rightfully so. These legacy communities get overlooked though. By spotlighting them, we hope people will support a corridor-wide plan that blends flood risk reduction with improved water conveyance and habitat.

Q: Are there other reasons you want to spotlight these communities?

A: Absolutely. This corridor carries a lot of the water that moves from Northern California to Southern California. There are multi-benefit opportunities here, nature-based solutions, restored wetlands, and setback levees, that can reduce flood risk and at the same time improve water conveyance. It’s not just about keeping people dry; it’s about blending flood management with better water management.

Q: Many of these towns are low income, disadvantaged communities and can’t afford flood insurance. How does that financial reality shape your planning?

A: A lot of these communities are financially constrained. FEMA looks at the levees out there today almost as if they don’t exist, so the National Flood Insurance Program premiums are extremely high. Residents simply can’t afford those rates, even though the levees do provide some protection. And remember—when a levee fails out here, it’s not shallow flooding. We’re talking ten feet of water or more and possibly over the rooftops of dwelling units. That reality drives us to look for different insurance models and alternative ways to fund improvements.

Q: You mentioned “deep flooding.” What does that term mean in practice?

A: From the state’s perspective, shallow flooding is anything less than three feet. Deep flooding is anything greater than that. In this corridor, you’re talking about 10 feet of water or more if a levee breaches. Part of the reason is that these levees are built on reclaimed tidal lands with peat soils that have subsided over time. Ground levels have dropped while the river and tidal levels remain the same and are increasing with climate change. Many of these levees are also frequently loaded by daily tidal changes, which makes them more vulnerable than levees inland.

Q: Isleton is pioneering a community-based flood insurance pilot program. Can you tell us about it?

A: Isleton’s pilot is part of the Delta Geological Hazard Abatement District, or GHAD. It sort of functions like a glorified homeowners’ association that resides outside of the city council, providing direct access to residents without government intervention. With help from the California Department of Water Resources, the GHAD buys a single policy that covers the whole community. There’s a staff gauge near Isleton’s wastewater treatment pumping plant facility that’s electronically monitored. If water hits that gauge due to shallow or deep flooding, the policy pays out to the community. The residents decide how to distribute the money equitably. It’s not individual insurance; it’s about helping the whole community recover quickly. We hope to replicate that model in other Delta towns and eventually across the greater Central Valley.

Q: You’ve been involved in the Small Community Flood Risk Reduction Program. What did those studies reveal?

A: Between 2019 and 2022 we completed eight studies in this corridor, all funded by the state. I wrote grants for ten or so and led six of the studies myself. The takeaway is that these levees fall well short of FEMA accreditation. They’re tall but, but they’re loaded daily by the daily tidal exchange. Other Central Valley levees don’t see that kind of constant pressure. There has also been documented land and levee subsidence with the Delta’s the peat soils – flood depths that might have been ten feet a century ago could now be fifteen or twenty. That just underscores the urgency to improve the quality of said levee systems in the Delta.

Q: What challenges do you foresee in scaling up the GHAD and community-based insurance?

A: The biggest challenge is getting communities to adopt it. The NFIP insurance is so expensive that people are willing to try something different, but it still takes trust. Our model is parametric: if the gauge shows water, there’s a payout, and the community decides how to use it. It’s about recovery, not response. Once people see how it works in Isleton, we think others will follow. We’re already talking about expanding it to other Delta legacy Communities and eventually to small communities across the greater Central Valley.

Q: The state is also considering the Delta Conveyance tunnel. Where does that fit into plans?

A: The tunnel isn’t a silver bullet. Even with a tunnel, about 80 percent of the water will still move through the existing channels as under present conditions. We’re going to rely on these levees for decades. Some of the State water contractors are beginning to realize this which is good. Upgrading the corridor’s levees would cost less than $4 billion. That’s a bargain compared to the tens of billions being discussed for the conveyance project. We need both flood protection and reliable water conveyance, and a corridor wide management plan could collectively advance both efforts.

Q: Your abstract mentions the Great California Delta Trail. How does that relate to flood risk reduction?

A: The Delta Protection Commission (DPC) adopted a strategic masterplan in January of 2022 for a recreational trail that would connect trails in the East Bay to the American River and eventually to the Pacific Crest Trail. I’ve helped with the planning behind some of the trail segments along the Sacramento River corridor. The trail would pass by these legacy communities and even allow for travel by personal watercraft on some stretches. It’s about agritourism and local commerce as much as recreation. When we upgrade levees, we can include trail segments on the crown or landside berms. It’s another way to bring investment to the corridor while improving flood protection.

Q: Has anything surprised you as you’ve worked on this corridor plan?

A: I wouldn’t say there have been huge surprises. Maybe the biggest eyeopener was hearing from our colleagues on the Delta Conveyance project that even with a tunnel they’ll still need to move water along the existing route. It just further reinforces for me that we can’t ignore these levees. We have to reinforce them for both flood safety and water conveyance.

Q: What milestones or decisions should people watch for over the next few years?

A: Keep an eye on the Central Valley Flood Protection Plan update for 2027. Our work falls under the Lower Sacramento–Delta North Region. Billions have been spent protecting urban areas and enhancing the Yolo Bypass, which is great, but these legacy communities haven’t been getting the same attention. They’re part of a National Heritage Area. Some are culturally unique—Locke, for example, is the only U.S. town built by and for Chinese immigrants. We’re trying to get a corridor management plan included in the CVFPP, so these places have a bigger seat at the table.

Q: How can engineers, planners, policymakers and residents help make your vision a reality?

A: It starts with listening to the communities. They’ve historically been opposed to isolated conveyance because they worry about water quality and the impacts of their environment. Engineers and planners need to keep those concerns front and center. Local residents also need to come together and speak with a unified voice about what they want. My hope is that by working together, combining technical expertise with local knowledge, we can reduce flood risk, improve water reliability, and preserve the character of these Delta Legacy Communities.

Q: Any last notes for those who may be attending FMA or are interested in this topic?

A: I hope people will stop by and listen. We’re trying to give the Delta Legacy communities a larger voice in regional planning, and we need partners at every level to make that happen.