Bay Sediment Budgets:Sediment Accounting 101

David SchoellhamerMegan LionbergerBruce JaffeNeil Ganju Scott WrightGreg Shellenbarger U.S. Geological Survey

NASA

A sediment budget describes the quantity of sediment

• Entering the Bay

• Leaving the Bay

• Depositing in or eroding from the Bay

Who cares?

• Dredgers: disposal of deposition in ports and channels

• Regulators and dischargers: sediment associated contaminants and TMDLs

• Restoration managers: deposition needed for restoration without eroding existing habitat

Accounting rules

• Where: SF Bay from Mallard Island to Golden Gate

• When: Water years 1955-1990, 1995-2002, and a normal water year 1995-2002

• Lifeline: Conservation of mass: inflow-outflow=change in storage

• Uncertainty: varies by term, “Not THE answer” – Steve Ritchie

Odgen Beeman and Krone 1955-1990

New information for 1955-1990

Term OBK New information

Supply from Delta No deposition in Delta

Delta sediment outflow 1/3 of inflow

Bathymetric change

Data from navigation charts

Data from actual surveys

Sand mining Assumed zero Rough estimate

Revised 1955-1990 annual budget

Units are mass in millions of metric tons per year (~1.5 Mcy)

Revised 1955-1990 annual budget

Assume Krone Central Bay deposition is ocean sand

Revised 1955-1990 annual budget

Suspended sediment outflow from conservation of mass (lifeline)

Revised 1955-1990 annual budget

Sand mining is a very rough estimate

1995-2002 annual budget

1995-2002 annual budget

Box model used to get change in storage and outflow

1995-2002 annual budget

Assume no change in supply of ocean sand

1995-2002 was all wet

0100200300400500600700800900

1000

Del

ta o

utf

low

, m

3/ s

1995-2002 1955-1990 1996,1997,1999-2002

Normal 1995-2002 annual budget

Remove water years 1995 and 1998 where possible

1995-2002

1955-1990

1955-1990

1995-2002

1955-1990

1995-2002

1955-1990

1995-2002

1955-1990

1995-2002

1955-1990

1995-2002

Implications

• Sediments disposed of in the ocean may be needed to maintain and restore Bay habitats

• The Bay bottom will continue to erode and supply legacy contaminants

• Restoration sites will be depositional and may increase erosion elsewhere

• Dredging, restoration, and water quality are connected by the sediment budget

Most important and most uncertain terms

• Golden Gate fine suspended sediment outflow (model because difficult to measure)

• Golden Gate sand supply, 1.2-2.9 MMT/yr (Central Bay bathymetric change)

• Eroded mass (new surveys, measure bed density)

• Sediment supply from watershed (±25%)

Acknowledgements

•U.S. Army Corps of Engineers•SF Regional Water Quality Control Board•California State Coastal Conservancy•USGS Priority Ecosystem Science Program•USGS Federal/State Cooperative Program

•Lester McKee•Patricia Chambers and Linda Wanczyk