Trends in Suspended Sediment Input Trends in Suspended Sediment Input to the San Francisco Bay to the San Francisco Bay from Local Tributaries from Local Tributaries Presented by Setenay Bozkurt [email protected]Philip Williams & Associates, Ltd. San Francisco, CA December 2005
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Trends in Suspended Sediment Input to the San Francisco Bay from Local Tributaries Presented by Setenay Bozkurt [email protected] Philip Williams &
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Trends in Suspended Sediment InputTrends in Suspended Sediment Inputto the San Francisco Bayto the San Francisco Bay
19 watershedsLook for correlation of suspended sediment yield with:
– drainage area– annual runoff– relief– % sand in soils– % area with landslides– mean annual precipitation– rainfall threshold statistics– % area with steep slopes– % sandy soils– % area of rangeland and barren land– % area of rangeland with steep slopes– % impervious area
SPATIAL CORRELATIONS
Significant correlations between sediment yield and
Compare sediment concentrations for a given discharge range over long term
TEMPORAL TRENDS IN SUSPENDED SEDIMENT RECORDS
Alameda Creek
Colma Creek
Cull Creek
San Lorenzo Creek
2 - 10% Qw Range10 - 20% Qw Range
-1 -0.5 0 0.5 1
No Trend
Negative Small / ModerateTrend Positive Small / ModerateTrend
Kendall Tau Value
PREDICTING SUSPENDED SEDIMENT INPUT TO THE BAY
Sediment rating curves: Qs vs. QSediment loads correlated well for all stations
r2 > 0.70Scatter due to:
– Inherent random changes in any system at any given time– Nonlinear relation between discharge and concentration– Hysteresis and sediment lag of floods
Better correlation and predictability if low discharges are excluded