Abstract
Sedimentation in the Sacramento–San Joaquin River Delta builds the Delta landscape, creates benthic and pelagic habitat, and transports sediment-associated contaminants. Here we present a conceptual model of sedimentation that includes submodels for river supply from the watershed to the Delta, regional transport within the Delta and seaward exchange, and local sedimentation in open water and marsh habitats. The model demonstrates feedback loops that affect the Delta ecosystem. Submerged and emergent marsh vegetation act as ecosystem engineers that can create a positive feedback loop by decreasing suspended sediment, increasing water column light, which in turn enables more vegetation. Sea-level rise in open water is partially countered by a negative feedback loop that increases deposition if there is a net decrease in hydrodynamic energy. Manipulation of regional sediment transport is probably the most feasible method to control suspended sediment and thus turbidity. The conceptual model is used to identify information gaps that need to be filled to develop an accurate sediment transport model.
Highlights
The Sacramento–San Joaquin River Delta (Delta) is where the rivers of the Central Valley of California merge to become the San Francisco Estuary (Figure 1)
A sedimentation model was included in the Delta Regional Ecosystem Restoration Implementation Plan (DRERIP) suite of conceptual models because sediment deposition creates and sustains the Delta landscape, pelagic habitat depends on suspended sediment, and sediment transports adsorbed nutrients and contaminants
Emergent macrophytes and Egeria densa act as ecosystem engineers that can create a positive feedback loop for sedimentation. This feedback loop helps explain the successful invasion of the Delta by Egeria densa since the 1960s and its effect on Delta turbidity
Summary
The Sacramento–San Joaquin River Delta (Delta) is where the rivers of the Central Valley of California merge to become the San Francisco Estuary (Figure 1). The model includes submodels for river supply, regional transport, and local sedimentation in open water and marsh habitats. Porterfield 1980; Wright and Schoellhamer 2005) have documented how the Sacramento River dominates in contributing sediment to the Delta The structure of this conceptual submodel, is such that it could be used to describe the sediment supply from any of the Central Valley watersheds. Tidally-averaged sediment transport is usually from the Delta into Suisun Bay. For water years 1999 to 2002, Mallard Island suspended sediment flux was seaward, and 51% of the Freeport sediment discharge (Wright and Schoellhamer 2005). Large sediment supply during the period of hydraulic mining in the late 1800s caused deposition in Sacramento Valley rivers, the Delta, and San Francisco Bay (Gilbert 1917). Restoration of tidal flooding to diked lands can increase tidal prism and tidal velocities in channels adjacent to the restoration site, which in turn can erode the channels (Kirby 1990)
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