Document Details

DRERIP Ecosystem Conceptual Model: Sedimentation

David Schoellhamer | November 13, 2007
Summary

1) Sediment supply: The supply of sediment from the watershed to the Delta is limited.  Sediment supply is decreasing due to trapping behind dams and diminishment of the hydraulic mining sediment pulse.
2) Sustainability: The Delta is depositional and adequate sediment deposition is required for wetlands to keep up with sea level rise.
3) Restoration: Typical suspended-sediment concentrations in the Delta range from 10-50 mg/L except during river floods when it can exceed 200 mg/L. Natural wetland sedimentation when concentration is 100 mg/L is about 0.025 m/yr, so deposition rates in the Delta are smaller.
4) Light and biota: Suspended sediment is the primary attenuator of sunlight in the water column of the Delta. Photosynthesis, primary production, and fish behavior depend on light.
5) Model uncertainty: Physical processes are qualitatively understood but difficult to quantify. Erosion is more difficult to quantify than deposition. Biological processes that affect sedimentation are not as well understood qualitatively and are very difficult to predict quantitatively.

Outcomes
The four primary outcomes of this conceptual model are:
1) Bed sediment character (size, organic content)
2) Geomorphic change
3) Suspended sediment character (concentration, organic content, settling velocity)
4) Water column light
These outcomes are used by habitat, stressor, and species models. The first three outcomes are also drivers in this model because of feedback loops. This conceptual model also has many intermediate outcomes that are used as drivers in the model and are available to other models.

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Product Description

1) Sediment supply: The supply of sediment from the watershed to the Delta is limited.  Sediment supply is decreasing due to trapping behind dams and diminishment of the hydraulic mining sediment pulse.
2) Sustainability: The Delta is depositional and adequate sediment deposition is required for wetlands to keep up with sea level rise.
3) Restoration: Typical suspended-sediment concentrations in the Delta range from 10-50 mg/L except during river floods when it can exceed 200 mg/L. Natural wetland sedimentation when concentration is 100 mg/L is about 0.025 m/yr, so deposition rates in the Delta are smaller.
4) Light and biota: Suspended sediment is the primary attenuator of sunlight in the water column of the Delta. Photosynthesis, primary production, and fish behavior depend on light.
5) Model uncertainty: Physical processes are qualitatively understood but difficult to quantify. Erosion is more difficult to quantify than deposition. Biological processes that affect sedimentation are not as well understood qualitatively and are very difficult to predict quantitatively.

Outcomes
The four primary outcomes of this conceptual model are:
1) Bed sediment character (size, organic content)
2) Geomorphic change
3) Suspended sediment character (concentration, organic content, settling velocity)
4) Water column light
These outcomes are used by habitat, stressor, and species models. The first three outcomes are also drivers in this model because of feedback loops. This conceptual model also has many intermediate outcomes that are used as drivers in the model and are available to other models.

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DRERIP_Sediment_Conceptual_Model_for_final_sign-off_2007-082

Keywords:

modeling, native fish, Sacramento–San Joaquin Delta, sediment