Shore & Beach  Vol. 85, No. 2  Spring 2017 Page 2 S an Francisco Bay is the largest estu- ary on the U.S. West Coast, and the second largest in the United States; combined with the contiguous Sacramen- to-San Joaquin Delta it covers a total sur- face area of ~4,100 km 2 and a watershed area of ~162,000 km 2 . It contains several economically signiicant harbors ($20 bil- lion worth of cargo annually) in one of the most developed regions of the United States, with a surrounding population of over seven million people. San Francisco Bay and the adjoining Delta are among the most human-altered estuaries and hy- drologic systems, respectively, in the world. Major historical changes were driven by the extensive hydraulic mining inlux of sediment in the late 19th century, massive alteration of the drainages entering San Francisco Bay in the 20th century, and the enormous amounts of sediment removed throughout the San Francisco Bay Coastal System from the early part of the 20th cen- tury to the present.” (Barnard et al. 2013) O ver the last 6,000 years, there has been a steady and exponential expansion in the global amount of earthen material altered by human actions. Today we afect hydrogeological processes more than at any other time in history, mainly by accelerating and decelerating lows of these materials and by physically altering their composition (Hooke 2000). Some of these efects are the unintentional by-product of other activities, such as the acceleration of ero- sion through deforestation, development, Sediment is critical infrastructure for the future of California’s Bay-Delta By Brett Milligan U.C. Davis, bmilligan@ucdavis.edu Rob Holmes Auburn University, rbh0012@auburn.edu ABSTRACT In coastal and estuarine regions, sediment is a crucial resource that should be rec- ognized as such and managed for its infrastructural role as substrate for a myriad of important human and environmental processes. his paper uses California’s Bay-Delta as a case study to both show this signiicance and to develop recommendations for the management of sediment as infrastructure. he paper presents selections from and distillations of a longer report that describes the background, methods, and indings from DredgeFest California. his event, held in the Bay Area in June 2016, brought together designers, scientists, engineers, regulators, and policymakers to examine the future of sediment design in the Bay-Delta. ADDITIONAL KEYWORDS: Sedi- ment management, design with sedi- ment, dredging, coastal resilience, climate change adaptation. Manuscript submitted 31 January 2017, revised and accepted 30 March 2017. and agriculture or the deceleration of sediment when it is trapped behind dams in reservoirs. Other forms of earth mov- ing are intentional and directed, such as mining, the construction of levees, or dredging. Dredging is particularly instructive because it marks a transition between typically unintentional acceler- ated erosion and the intentional work of removing sediment from waterbodies and placing it elsewhere (Holmes and Milligan 2013). In estuaries and other coastal regions, the sediment that experiences these ma- nipulations is a crucial resource as it is the physical substrate underlying many highly-valued landscapes, landforms, and processes. Ecosystems, communi- ties, and economic activity rely on this dynamic infrastructure. However, in nearly all coastal and deltaic regions, sedimentary regimens have been highly altered by human intervention, radically afecting sediment distribution (Renaud et al. 2013). Sediment availability is lim- ited and shortfalls are exacerbated by the uneven geographic allocation of sediment — landscapes that need more sediment oten cannot obtain it readily, while other landscapes experience excesses that gen- erate problems such as unwanted siltation and associated management expenses. The case of California’s Bay-Delta demonstrates these issues well. Sediment is critical to the present and future health of California’s Bay-Delta. As the most recent State of the Estuary report notes: “Like freshwater, sediment is a precious resource that is essential for keeping the Estuary healthy” (San Francisco Estuary Partnership 2015). But the Bay-Delta currently has a shortfall of this land- making resource. Upriver dams have trapped sediment (Minear and Kondolf 2009). Levees, bank armoring, and river straightening have cut of wetlands and loodplains while accelerating the move- ment of sediment, preventing it from building new substrate (Schoellhamer et al. 2013). he Bay’s coastal wetlands and subsided former marshlands that are behind dikes, which are critical to sea level rise adaptation, have new sediment needs, potentially requiring as much as 200 million cubic yards of sediment over the next 15 years to efectively restore them to established Baylands ecosystem goals (San Francisco Bay Conservation and Development Commission 2015). Moreover, this projection does not ac- count for the ongoing and longer-term need for sediment to maintain marsh elevations in the face of sea level rise. In the Delta, many levees are now protecting subsided “islands” that are up to 20 feet below sea level, stressing the levees — and with them local communities, ecolo- gies, and the role of the Delta as conduit for southern California’s water supply (Luoma et al. 2015). Sediment, including dredged material, is one of the primary materials available to meet these current and future challenges. The nature of managing the Bay- Delta’s emerging conflicts between supply and demand for sediment is just beginning to be discussed, contested, and grappled with. he precise manner of its realization will afect policy, dredg- ing operations and priorities of future