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Suspended Sediment Loads from Bay Area Small Tributaries Mikolaj Lewicki and Lester McKee Sources Pathways and Loading Workgroup May 14 th 2008 Item #3a 1

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Project Impetus Hg and PCB load calculations in the TMDLs are based on estimates of suspended sediment loads Krone 1979 (750,000 t) Davis et al., 2000 (320,000 t) Bay modeling would benefit from accurate spatially explicit estimates Wetland restoration projects also require sediment source information

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Available Data Sets 29 USGS Sediment Gages 135 years of record for all the stations Does it mean that we have enough information ? Is the field data collected in the locations that provide the most information Is the distribution of sampling stations dense enough to include the diversity in land use, lithology, or physiography? Item #3a 3

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Suspended Sediment Discharge from the Ungaged Watersheds Potential statistical relationships between a watershed characteristic and suspended load – Drainage Area – Annual Discharge – Annual Peak Discharge – Land Use – Geology – Slope – Other Item #3a 4

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Drainage Area vs. Suspended Load There is a weak relationship between drainage area and the load. Correlation is better for more uniform geomorphic/climatic provinces Item #3a 5

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Which variable is statistically the most significant for the total annual load predictions? Drainage Area Annual Discharge Unit Annual Peak Discharge Correlated with Unit Sediment Load Land Use Geology Watershed average slope ? And the winner is… Annual Peak Discharge Item #3a 6

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Unit Annual Peak Discharge Correlated with Unit Sediment Load East Bay Very Good correlation R 2 = 0.94 Item #3a 7

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Unit Annual Peak Discharge Correlated with Unit Sediment Load North Bay Item #3a 8 Very Good correlation R 2 = 0.92

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Unit Annual Peak Discharge Correlated with Unit Sediment Load San Francisco Peninsula 9 Item #3a Correlation could be improved by low discharge sampling and better understanding of urban watersheds sediment loads

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Unit Annual Peak Discharge Correlated with Unit Sediment Load San Francisco Bay 10 Item #3a

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Other Statistical Correlations 11 Unit Annual Peak Discharge Correlated with Unit Sediment Load for Each of the SF Bay Counties Item #3a

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12 Item #3a Other Statistical Correlations Unit Annual Peak Discharge Correlated with Unit Sediment Load for Each of the SF Bay Counties

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Other Statistical Correlations #2 13 Unit Annual Peak Discharge Correlated with Unit Sediment Load for different types of Geology (classified based on the rock formations resistance to erosion) Item #3a

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14 Item #3a Other Statistical Correlations #2 Unit Annual Peak Discharge Correlated with Unit Sediment Load for different types of Geology (classified based on the rock formations resistance to erosion) Lower sediment discharge from resistant geology

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Each watershed was divided into fife generalized land use classes (based on NLCD data set) – Natural – Agriculture – Low density urban – High density urban – Industrial 15 Item #3a Other Statistical Correlations #2 Unit Annual Peak Discharge Correlated with Unit Sediment Load for different land use types

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Other Statistical Correlations #238 16 Unit Annual Peak Discharge Correlated with Unit Sediment Load for different land use types Item #3a Natural land use type has lower sediment discharge compared with urban land use type

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Remaining Work 17 Item #3a Correlate Unit Annual Peak Discharge with Unit Sediment Load for different median watershed slopes Correlate Unit Annual Peak Discharge with Unit Sediment Load for areas with high number of construction sites Log Ys= 0.059C-0.047 Ys suspended sediment yield in tons / acre C percentage of land under construction

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18 Item #3a Remaining Work Correlate Unit Annual Peak Discharge with Unit Sediment Load for mature urban watersheds Natural Areas Sediment yields 0.02 - 0.03 tone / acre/year Urban / Residential Areas 3.9 tone / acre/year Grass Areas 0.2 tone / acre/year Correlate Unit Annual Peak Discharge with Unit Sediment Load for watersheds with land slides or forest fires Both processes are expected to increase sediment loads at least 30 times compared to the background values Croplands 3.6 tone / acre/year

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Questions / Comments Item #3a 19

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