Delta plain accretion rate among systems compared to sea level rise

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Delta projects will accrete at a rate sufficient to restore historical wetlands and will keep up with sea level rise, given restoration of tidal prism and adequate connection to river flows that contain sufficient suspended load.

On many deltas, the delta plain has subsided following agricultural development. River system sediment and large wood budgets are commonly reduced, and suspended sediments may be piped through delta systems by levee infrastructure. The unusual delta plain structure in partially restored delta ecosystems may create delta forming conditions very different from those observed in naturally forming deltas. A learning project to evaluate on-site sediment dynamics will necessarily consider changes to river basin processes in addition to project design elements, and consideration of alternative treatments, control, and reference sites. Learning is useful to the extent that it can improve future project selection and design.

Delta Strategy Analysis

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The uncertainties in how this topic affects delta restoration has resulted in its inclusion in the ESRP River Delta Adaptive Management Strategy. This three criteria analysis should build off the analysis above, and supports development of learning projects.

Importance Viability Policy Relevance

Elevation and salinity are two of the main determinants of vegetation composition, habitat structure, primary production, and is an indicator of system resilience to climate change. We have almost no basis for describing the sediment regime within a large Puget Sound delta, and how this reflects on future delta conditions.

Methods for evaluating sediment budget, routing and deposition rate are known, and while requiring careful design, robust data could be obtained.

This knowledge may affect which deltas are anticipated to provide resilient restoration benefits, and provides a full picture of restoration cost over time in systems with insufficient sediment inputs. This knowledge could strongly affect regional allocation of assets, or redefine system scale restoration needs.