Not Enough: A Study of Sediment Management Practices and the Habitat Goals in the San Francisco Bay

Abstract

A regional effort to restore historic estuarine habitat in San Francisco Bay has become enmeshed with climate change adaptation planning, as research has demonstrated a number of infrastructural benefits that come with healthy tidal habitat. However, the achievement of both biodiversity and practical objectives is currently being jeopardized by a massive sediment debt. The sediment debt has been created by a number of human activities, including mining, agricultural land conversion, diking, hydropower conversion, dredging, and pollution. Over time, this has caused the Bay shoreline to subside dramatically below sea level and has also reduced sedimentation rates. As a result of these reduced sedimentation rates, it seems unlikely that subsided lands will be able to be restored before sea levels begin to rise at a faster rate. In order to protect the shoreline and upland areas, restoration projects have begun to import sediment from external sources like dredging or construction activity in order to speed up the process of natural sedimentation and accrete wetlands to sea level before sea levels begin to rise. This thesis estimates the total capacity of sediment required to meet broader regional restoration goals set by the Baylands Ecosystem Habitat Goals Report as 280 million cubic yards. If tidal action were restored to the entire shoreline today, it would take natural sedimentation rates over 70 years to close this gap in some locations. Thus, this paper considers the problem of how to allocate sediment to projects so that broader restoration goals can be accomplished. Given that the main external source of sediment used by restoration projects—dredging activities—only yields 3-5 MCY per year, careful consideration by policymakers will be required to expand sediment supply and maximize reuse in shoreline areas. Unfortunately, sediment management organizations like the Army Corps of Engineers have managed the looming sediment shortage rather poorly. Regulators need to take steps to improve permitting processes, establish lines of communication between restoration projects and dredgers, and incentivize higher rates of reuse by dredgers and construction firms. Furthermore, higher proportions of funding need to be directed towards scientific research, which is critical to the success of the Habitat Goals report.