Revealing Risk: An Historical Ecology of Flooding in the Pájaro Valley

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Danielle Zoe Rivera, Lead Landscape Architect
Eliza Breder, Graduate Student Researcher

Revealing Risk addresses a core limitation with contemporary flood risk theories and modeling: that it lacks an historic focus. The temporal aspects of flood risk creation are crucial: they can unveil repeatedly poor flood response and point to hazards that need to be redressed to avoid future flood events. To address this, our team developed new research processes leveraging historical ecology and archival research to, first, unearth the histories of flooding and flood risk creation in California’s Pájaro Valley, and second, identify areas for improving flood recovery and reconstruction following the 2023 Winter Storms. These findings were shared with community partners and the U.S. Army Corps of Engineers to positively influence the community’s flood recovery. From a public report and exhibit, we were able to assist in identifying weak points in the region’s water infrastructure, and direct recovery funds to the region’s historically overlooked communities. 

Revealing Risk focuses on the Pájaro Valley (Valley) of California to assist in post-flood recovery and reconstruction following the 2023 Winter Storms. Our design group has been conducting community-engaged research in the Valley for five years and, working with our community partners, two critical questions repeatedly arise: 

How often do floods like the 2023 Winter Storms occur in the Pájaro Valley? And, what has or hasn’t happened in the past to address our flood risk? 

While simple flood risk modeling might address these questions on the surface, it was clear residents were more deeply concerned with the impacts of repeated flooding and a perceived lack of response addressing their flood risk. This corresponds to emerging research in design and planning on the social nature of flood risk creation: namely that static definitions of what makes certain groups more vulnerable to hazards are too focused on individuals or individual neighborhoods, missing how these risks are generated in/through time. To avoid that pitfall, we take a procedural and contextual vulnerability approach to examining flood risk creation — a theoretically solid approach, but one for which the methods are still developing. We leverage the traditions of historical ecology and its visualization in the design professions to fill this gap. 

Given the auspicious timing of the project, its goal was also to inform recovery and reconstruction efforts following the 2023 Winter Storms. To this end, we partnered with the environmental justice and nature-based solutions offices at the United States Army Corps of Engineers – San Francisco (ACE) to directly inform levee re-designs being proposed for the Pájaro Valley. 

Our work examined the history of the Pájaro Valley’s waterways, flood risk development, and flood events, combining material from eight archives across California. We created a database of relevant news articles, photographs, maps, reports, documents, and stories concerning flooding, flood risk, and development in the region. Additionally, this was supported by a geospatial analysis of physical changes and urban development in the region from 1850 to 2025, using spatialized data from USGS and The Bancroft Maps Library. These sources were cross analyzed using an historical ecology framework for studying flood risk which cataloges: physical flood risk creation, contextual and procedural vulnerability to flooding, and governance/planning developments. This analysis revealed four distinct eras of flood risk creation over the Pájaro Valley’s history, each defined by distinct socio-political attitudes towards flood risks and flooding. These eras are represented in a Flood Risk Timeline and high-level summaries of major mitigation events, physical environmental changes, and resident stories of key events. 

The findings from this analysis were compelling, challenging some fundamental “common knowledge” assumptions: whereas the ACE and community leaders believed flooding only occurs in the region once every 10-20 years, we showed that between 1850 and 2025 a major flood occurred on average once every five years. We also found that floods tended to occur in the same locations along regional waterways, and that these weakened areas corresponded to historic changes made to their courses. Lastly, we discovered patterns of racial segregation, in which the local farmworkers were historically pushed into the region’s riskiest areas. Unsurprisingly, this produced a pattern of broken promises to these communities whereby major floods occur, promises to fix regional infrastructures are made, but projects are repeatedly left unfunded. 

From these findings, we prepared a public report for the ACE and our community partners, making the history and findings accessible for a wide audience and outlining key takeaways for responses to the 2023 Winter Storms. We also created an exhibit inspired by the report’s Flood Risk Timeline to further share our data and findings, adding spatial and tactile presentation for a wider audience. This work helped direct attention to the physical areas of repeated flooding through time prevented the defunding of projects in the highest risk areas of the Pájaro Valley, interrupting an historical pattern where the minimal influence farmworkers hold politically in the region typically led to underinvestment. In all, we were able to assist real planning and design processes by looking beyond contemporary, static flood risk maps and modeling, to instead show how and why these risks develop and persist in the Pájaro Valley, charting a path to better outcomes for all residents.