Sediment for Survival

Managing sediment at the scales needed to take advantage of natural processes in watersheds, the Bay, and the Delta will require reworking of the approach to management and coordination currently in place. For example, sediment management currently is rarely coordinated between watersheds and baylands, the Delta and the Bay, or a locality that begins to scour when accretion happens in another place. A set of principles that helps guide thinking and planning can aid the transition to a new approach. 

Sediment for Survival outlines nine guiding principles (A to I) based on scientific investigations and community processes related to understanding the estuarine ecosystem and preparing for climate change impacts (e.g., Goals Project 2015, Milligan et al. 2016, SFEI and SPUR 2019). The list below distills the ideas from these other efforts to include only the aspects most relevant to sediment management.

(A) Complete tidal marsh systems are the goal. 

(B) Geography matters; consider geography in planning. 

(C) Expect change, plan for multiple future states. 

(D) Take advantage of natural processes, which means managing sediment and water together. 

(E) Don’t take for granted current access to sediment, freshwater, and tidal flows.

(F) Combine management approaches into strategies. 

(G) Collaboratively implement strategies at the landscape scale. 

(H) Coordinate at the regional and estuarine scales. 

(I) Learn rapidly with a robust monitoring and adaptive management program.

To learn more, see pages 73-80 in the report.

Within the region, waste products are being viewed more and more as valued resources for bayland restoration and shoreline adaptation, causing a shift in thinking around how to manage these resources to address bayland sediment deficits and accelerate bayland peat production. While some materials that would likely be disposed of—such as dredged sediment and excavated soils—are already being used in baylands restoration, additional opportunities exist to support bayland resilience. Resources that could be used to increase organic and inorganic accretion include (1) tidal and fluvial sediment dredged or mined from the Bay, stored in and removed from flood control channels, and trapped behind dams; (2) upland sediment in the form of excavated soils that currently end up in landfills, biosolids generated from wastewater treatment plants, and construction and demolition waste (e.g., brick, concrete, masonry, gravel, and stone) that could be used as a polder fill alternative in adaptation planning to preserve mineral sediment for more direct biotic uses; and (3) treated wastewater as irrigation in horizontal levees to support organic matter accumulation in marshes. Although biosolids, construction/demolition waste, and treated wastewater via horizontal levees are not permissible at present, these resource streams could be viable in the future as research evolves and sediment deficits increase. For each opportunity, we quantify the known relative magnitudes when available and provide other salient details. 

To learn more, see pages 81-113 in the report. Refer to Appendix C for supplemental information used to calculate sediment mass for each source.

The sediment management measures (or actions) described above should rarely be implemented independently. Rather, to address sediment management objectives in watersheds and downstream baylands, measures focused on improving natural sediment processes and beneficially reusing sediment need to be combined to create sediment strategies (Figure 4.13). Strategies should be developed at the OLU scale through a collaborative process that includes a wide range of stakeholders, and should be adaptable over time as conditions change. They need to be built upon the best available science and site-specific information, with the measures included being selected based on an understanding of current and likely future conditions and through an examination of trade-offs. This section details the key steps at play when developing a place-based sediment strategy. 

• Processes for creating a place-based sediment management strategy:
• Compile information for local sediment supply and bayland sediment demand and consider range of future climate outcomes
• Develop a long-term vision for sediment management in watersheds and adjacent baylands that identifies multi-benefit management measures
• Assess management options through landscape scenario planning
• Construct a local strategy to implement watershed and bayland sediment management measures over time

To learn more about each process listed above, see pages 114-117 in the report.

The results from this study and many others provide the science that can be used as the building blocks of sediment strategies that support bayland resilience. However, many knowledge gaps remain with respect to understanding potential future conditions under a changing climate and the factors controlling bayland sediment demand and supply at a range of spatial and temporal scales. Many researchers have recently put forth ideas about the knowledge gaps pertaining to Bay sediment science that need to be addressed to improve management approaches (e.g., BCDC 2016, SFEI-ASC 2017a, Schoellhamer et al. 2018). Sediment Survival offers a list of some of the most high-level critical knowledge gaps specifically related to the assessment of future bayland demand compared to sediment supply is provided. 

To learn more, see pages 118-119 in the report.

Monitoring the conditions of baylands will be essential to assess their ability to keep pace with SLR and the degree to which sediment management actions are supporting long-term resilience. This includes frequent measurements of local sediment processes and topographic change (e.g., annual net sediment flux to a marsh, annual net sediment deposition rates on a marsh, shoreline erosion/progradation rates) and key bayland resilience metrics based on monitoring data (e.g., tidal flooding depth and duration). Currently, bayland monitoring is typically done at the site scale as part of project compliance required by regulatory agencies or by academic institutions and research organizations seeking to understand local processes (e.g., Buffington et al. 2020, Lacy et al. 2020). However, there are new efforts focused on a coordinated regional approach to bayland monitoring that provide recommendations for monitoring actions, locations, and frequency based on previous monitoring approaches and an assessment of what is needed to track bayland resilience over time. 

To learn more, see pages 120-124 in the report.