Q&A with Chris Ferrari on Flood Model Updates, Awareness Mapping, and the Delta Web Tool

By Quinn Fenger and Chris Ferrari

With 35 years of civil‑engineering experience in both the public and private sectors, Chris Ferrari has been instrumental in water‑resource projects across California. At this year’s Floodplain Management Association (FMA) conference, he’s involved in three sessions: a panel on the Central Valley San Joaquin River hydraulic model (CVFED 2.0) update, a technical session on the statewide flood‑risk awareness mapping for disadvantaged communities, and a presentation on the Sacramento County’s Delta Web Tool update used for real‑time flood operations. In this conversation, Chris explains why these tools matter.

Q: Let’s start with the basics—what are you presenting at FMA?

A: The first is a panel on the Central Valley Flood System Hydraulic Model update, which focuses on the San Joaquin River system. The second is about the GEI team has been supporting the state of California DWR in developing flood‑risk awareness mapping for disadvantaged communities. The third is a session on the Delta Web Tool, a real‑time flood‑operations dashboard for the Sacramento–San Joaquin Delta. The Central Valley session is a panel—DWR will kick things off then I’ll present about our work on model development and unexpected high snow amounts in 2023.

Q: Why was there a need for a new version of the Central Valley model (CVFED 2.0)?

A: The original model dates back more than a decade. Since then, a lot has changed—we’ve extended the model approximately 350 miles to seven upstream reservoirs, updated terrain data, and significant land subsidence in parts of the San Joaquin Valley. When we compared new topography to the 2008 terrain used in the first model, we were shocked at how much the ground had sunk. In some agricultural areas, subsidence reached up to approximately eight feet—the riverbed had essentially dropped vertically rather than slumping sideways. We found out essentially that groundwater over‑pumping has caused sections of the San Joaquin Valley River and portions of the tributaries to sink by approximately one-half foot per year, leading to expensive infrastructure repairs and water‑supply challenges. CVFED 2.0 includes the boundary conditions from seven upstream reservoirs and totals 870 miles of study streams.

Q: You mentioned subsidence. Was that the most surprising thing you found while updating the model?

A: Absolutely. We expected some sinking but seeing a vertical drop up to eight feet in a 30‑mile stretch was eye‑opening. It’s like an elevator lowering part of the riverbed. That’s why this update was essential—we needed to reflect the new reality to show what was occurring to the San Joaquin River levees and in the agricultural area.

Q: What’s the statewide flood‑risk awareness mapping project?

A: FEMA doesn’t map everywhere, so many small or disadvantaged communities don’t have modern flood maps. This project—now in its third phase—fills that gap. We’ve produced more than 500 miles of maps covering most disadvantaged communities outside the Central Valley. The mapping isn’t as detailed as the San Joaquin model, but it’s robust enough to identify flood‑hazard areas, especially on alluvial fans where floodwaters can spread unpredictably. Our main users are local agencies, emergency managers and planners. These maps help them understand where flooding could occur during high flows and are a first step toward official FEMA mapping.

Q: Who benefits from these awareness maps, and what’s next?

A: Local agencies, small towns, and counties use them to inform emergency planning and land‑use decisions. Many of these communities lack resources to commission detailed FEMA maps, so this program gives them actionable information. The next phase will move some areas toward FEMA Flood Insurance Rate Maps (FIRMs), which is a more involved process. We’re also leveraging readily available terrain data from USGS to keep costs down.

Q: Tell us about the Delta Web Tool. Why was it developed and how does it work?

A: After the Oroville Dam crisis in 2017, there was a clear need for better situational awareness in the Delta. In 2019 we received a grant from DWR and partnered with Sacramento County to build the Delta Web Tool. The Delta tool focuses on five Delta counties and includes 104 reclamation districts. There are tidal influences, riverine flows, and approximately 1100 miles of levees. Our tool brings together hydraulic‑model results, levee information, real‑time stream gauges, and terrain data into a single point‑and‑click dashboard. Emergency managers can pull up levee names, see flood forecasts, and view maps quickly without wading through separate datasets. It’s currently focused on Sacramento County but we’re expanding to include the counties of San Joaquin, Yolo, Contra Costa and Solano. Because it includes sensitive information, we’re not releasing it to the general public—but engineers and Delta stakeholders can access it.

Q: Is there any training planned for the Delta Web Tool?

A: Yes. As we hand the tool over from GEI to Sacramento County, we’ll provide training and support. The goal is for local agencies to use it effectively during flood events. We’ve kept the interface simple to ensure emergency managers can pick it up quickly.

Q: What do you hope conference attendees will take away from your sessions?

A: Awareness. Many people don’t realize these tools exist or that they were developed in‑house at GEI. We want to let practitioners know the CVFED 2.0 model is available, the awareness maps are being rolled out, and the Delta Web Tool can help manage flood risks in one of the most complicated floodplains area in the country. These projects have wide applicability whether you’re an engineer, a planner, or part of a local emergency‑management team. And, of course, if people have questions or want to collaborate, we’re here to help.