by Peter Moyle, Jeff Opperman, Amber Manfree, Eric Larson, and Joan Florshiem

Sacramento River meander migration, from 1904 to the present. Image credit: Amber Manfree

The flooding in Houston is a reminder of the great damages that floods can cause when the defenses of an urban area are overwhelmed.  It is hard to imagine a flood system that could have effectively contained the historic amount of rain that fell on the region—several feet in just a few days.  However, these floods are a stark reminder of the increasing vulnerability of urban areas across the world and the need for comprehensive strategies to reduce risk.  The evidence is clear that green infrastructure, as defined below, can increase the resiliency of flood management systems and, when managed for multiple services, can reduce flood risk for many people while also promoting a range of other benefits.

Floodplains provides an overview of floodplains and their management in temperate regions.

California has a history of large floods, some almost as dramatic as those that have devastated Houston. They occur just infrequently enough that many forget they can be a problem and then complain about cost of flood insurance.  During this past winter of record precipitation, California did a remarkable job of containing and diverting the water. Damaging floods were not an issue.  Of course, the 200,000 citizens of Oroville who had to be evacuated because of the threat of flooding from a broken dam spillway may feel differently.

Unfortunately, climate change models tell us that big floods in California may become bigger and more frequent in the future because there will be more rain and less snow as the result of warmer air temperatures.  Fortunately, in Central California, part of the solution for dealing with big floods already exists: the Yolo and Sutter Bypasses.  These huge floodplains fill with flood waters from the Sacramento River and its tributaries that cannot be contained by dams.  The floodwater is passed rapidly to the Delta and San Francisco Estuary, and then out under the Golden Gate over weeks and months.

Illustrated river-ecosystem concepts from Floodplains. Image credit: Amber Manfree

While flooded, the bypasses provide productive habitat for fish and waterbirds.  When not flooded, they are farmed or managed as wildlife areas. They are examples of “green infrastructure,” soft, flexible flood protection that also benefits the environment.  There are other examples from all over the world, although hard infrastructurelike walls, levees and dams is much more common.  In California, the new Central Valley Flood Protection Plan 2017 Update emphasizes investment in green infrastructure (although it is not called that in the plan) as a long-term approach to flood management.

We think the world needs a lot more such green infrastructure to meet the forecasted challenges and to support floodplain ecosystems that can also function for farming and recreation. Engineered floodplains are a prime opportunity for multi-benefit outcomes. We have documented this trend, and reasons why green infrastructure works so well, in a new book: “Floodplains: Processes and Management for Ecosystem Services”, published by University of California Press.

Our focus is reconciliation ecology, the science of integrating habitat for wild plants and animals into landscapes dominated by people. The book is based on our many years of studying floodplains in California, which is a leader in using floodplains for flood management.  But we also venture to other regions, especially Europe, Australia, and Asia, for new insights.   Towards the end, we provide 15 maxims to guide flood management such as “A bigger flood is always possible than the biggest experienced so far.”

“Our time spent on rivers and floodplains has certainly shown us that much has changed and been lost over time. But we have seen more than just glimmers of hope in reconciled floodplains that are diverse and productive. We take heart from the huge flocks of migratory white geese and black ibis that congregate annually on California floodplains and from knowing that, beneath the floodwaters, juvenile salmon are swimming, feeding, and growing among cottonwoods and rice stalks, before heading out to sea. We can envision greatly expanded floodplains that are centerpieces of many regions, protecting people but also featuring wildlands, wildlife, and floodplain-friendly agriculture. Connectivity among floodplains, people and wild creatures is within reach, as is a future in which people work with natural processes rather than continually fighting them.” (p. 218).

Peter B. Moyle is a UC Davis Professor Emeritus of fish biology and an associate director of the Center for Watershed Sciences. Jeffrey J. Opperman is a research associate at the Center for Watershed Sciences at the University of California, Davis and is the Global Freshwater Lead Scientist for World Wildlife Fund, working with teams across the world to develop and implement strategies to protect and restore rivers and floodplains. Amber Manfree is a postdoctoral researcher in Geography with the UC Davis Center for Watershed Sciences. Eric W. Larsen is a research scientist and fluvial geomorphologist in the Department of Human Ecology at the University of California, Davis. Joan L. Florsheim is a Researcher in fluvial geomorphology, hydrology, and earth surface processes at the Earth Research Institute, University of California, Santa Barbara.

Further reading

Opperman, J.J., et al. 2017. Floodplains: Processes and Management for Ecosystem Services.