Managing floods in mediterranean-climate Urban catchments: Experiences in the San Francisco Bay Area (California, USA) and the Tagus estuary (Portugal)

Abstract

The San Francisco and Lisbon estuaries share many geographical similarities, but their different governance makes for interesting comparisons. Many tributaries to San Francisco Bay were channelized by the US Army Corps in the 1950s-1970s. The design flaws of these projects (such as their having ignored sediment) are manifest as local governmentsnow struggle to maintain and operate them. Local agencies in the San Francisco region have used a range of innovative tools to solve these flood risk problems, such as creation of a new governance structure encompassing multiple jurisdictions around a stream, adoption of a 50-year plan to convert aging concrete channels into natural creeks, and implementation of projects that combine flood risk reduction with ecosystem and social benefits. Such a multi-purpose project built on the Ribeira das Jardas Stream near Lisbon has proven highly successful, especially as an urban social space.