Nisqually River Delta Sediment Budget and Assessment of Opportunities to Recovery Sediment Supply to Sustain Marsh
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In 2009, the largest estuary restoration project in the Pacific Northwest recovered tidal connectivity across 308 hectares of historic tidal marsh in the Billy Frank Jr. Nisqually National Wildlife Refuge (Refuge) and Nisqually River delta important for regional salmon recovery (Figure 1). The project represented a critical step toward restoring juvenile salmon habitat that experienced ~80-90% loss over the last 100 years in response to diking and draining wetlands for farming, grazing and other land use activities. A common effect of these land uses has been land subsidence and so while several valued ecosystem metrics were restored in the Nisqually Delta in 2009, the delivery of sediment to recover and sustain marshes remains a concern. As of 2022, marsh development has been limited to select areas of high topography. This study integrated numerical modeling and comprehensive field measurements to compute the sediment budget of the Nisqually River delta and evaluate the fraction of fluvial sediment delivery to the delta that accumulates in the restored estuary today and that could be realized with additional distributary channel restoration under existing conditions and projected higher sea level and stream runoff.
