THE NATURE CONSERVANCY
Over the past two centuries, efforts to control flooding have transformed California’s natural landscape. Rivers have been dammed and constrained by levees, wetlands have been drained and shorelines have been fortified against erosion. These projects opened land to urban and agricultural development but at a huge and ongoing cost to fish, migratory birds and other wildlife throughout the state. Roughly 10 percent of California’s historic wetlands remain, nearly all major streams have been altered dramatically and more than 100 miles of the state’s coastline have been armored with rock and concrete.
Despite these measures—implemented at great expense—significant risks to people and property remain. Coastal erosion threatens homes from San Clemente to Santa Barbara to Pacifica. Along the shores of San Francisco Bay, at least $29 billion in property, including major business centers, is currently at risk from a 100-year flood.
Climate change is expected to drive a combination of extreme weather and sea level rise that will increase the risk of flooding in California. The Intergovernmental Panel on Climate Change, the leading international body for the assessment of climate change, anticipates a significant increase in heavy precipitation events, translating to increased flood risk in many watersheds. The state Ocean Protection Council projects that sea level will rise five to 25 inches by 2050, and 17 to 66 inches by 2100.
Already, the state’s communities are considering how to respond to the growing risks. Much is at stake, as substantial resources likely will be devoted to protecting communities. For example, Louisiana recently adopted a $50 billion plan to prepare for rising sea levels and future storms.
As California considers how to adapt to a changing climate, planners often focus on defensive infrastructure with a negative habitat impact: bigger levees, rock walls to protect coastlines or even giant sea gates.
But California can follow a different path. With natural or “green” infrastructure that leverages natural processes to reduce risk to human lives, property and businesses, the state can build resilience to the coming changes while restoring natural habitats instead of degrading them.
“Green” or “natural” infrastructure can include a range of strategies. Some projects focus on preserving existing natural systems, while others are highly engineered, combining green techniques with more traditional “gray” approaches.
This report evaluates nine green infrastructure case studies in California. Each improves flood or coastal protection, provides habitat and preserves or restores the natural dynamics between water and land. We review the available data on the costs and benefits of each case and, where possible, compare this information with the costs and benefits of a gray alternative at the same site.
About the Nature Conservancy
The Nature Conservancy is the leading conservation organization working around the world to protect ecologically important lands and waters for nature and people.