Erica Gies is a journalist based in San Francisco, California, and the author of Water Always Wins: Thriving in an Age of Drought and Deluge (Univ. Chicago Press, 2022).
San Jose was flooded in 2017 when storm water in Coyote Creek was funnelled into the city.Credit: Noah Berger/AFP via Getty
Coyote Creek’s waters rose fast in February 2017 amid a series of storms. Rainfall filled the small river in northern California, which runs 103 kilometres from its headwaters near Morgan Hill to San Francisco Bay. In San Jose, where the river was forced into a channel tightly constrained by development, water surged from the creek. The resulting flooding forced 14,000 people to evacuate and caused more than US$73 million of damage.
In the wake of the disaster, environmental activists opposed to San Jose’s sprawl into Coyote Valley on the city’s southern edge saw an opportunity. Their plan was to convince San Jose officials that the city could avoid worse flooding by choosing not to pave over some of the last open space in the watershed.
Nature Outlook: Cities
Their approach has solid scientific roots. When land is paved, rain cannot soak into the soil, increasing the risk of flooding. One study1 found that, for every 1% increase in the area of roads, pavements and car parks, the annual flood magnitude in nearby waterways increases by 3.3%.
A growing understanding of this connection has led many cities to start de-paving small areas, digging and planting bioswales to absorb storm-water run-off, offering incentives for green roofs, and levying higher taxes on properties with a lot of impervious surface area. But the proposal by San Jose’s environmentalists was different. Their aim was not to make the city itself more permeable to water, but to reduce the risk of flooding by taking action upstream in the watershed, beyond the city’s urban footprint.
The 2017 flood provided the impetus to act. In the following year, San Jose’s voters approved a bond for about half of the $93 million required to buy 380 hectares of North Coyote Valley. “I don’t think we would have considered putting it on the ballot, or even considered that flooding was an issue, until we were devastated by the water damage in San Jose,” says the city’s current vice-mayor, Pam Foley.
The city of San Jose and conservation organizations have invested more than $120 million in purchasing 600 hectares of land in north and mid Coyote Valley. In 2021, the city council voted unanimously to change the land-use designations for the area, effectively barring any new development.
San Jose’s conservation of Coyote Valley reflects how land care is increasingly seen as crucial to managing flood risk. This marks a radical departure from the twentieth-century approach of trying to engineer water into submission. Conventional flood defences might also be needed, but San Jose is not alone in adopting more-natural methods of water management.
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