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Suspended Sediment Loads from Bay Area Small Tributaries
Mikolaj Lewicki and Lester McKeeSources Pathways and Loading Workgroup
May 14th 2008
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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
Available Data Sets• 29 USGS Sediment Gages
• 135 years of record for all the stations
Alameda Ck. At Niles
Guadalupe R. At San Jose
Coyote Ck. Above Highway 237 At Milpitas
Coyote Ck. Near Gilroy
San Francisquito Ck. At Stanford
Sonoma Creek At Agua Caliente
Walnut Ck. At Concord
Cull Ck. Above Cull Ck. Reservoir Near Castro Valley
Cull Ck. Below Cull Creek Dam Near Castro Valley
San Lorenzo Ck. Above Don Castro Reservoir Near Castro Valley
Colma Ck. At South San Francisco
Arroyo Valle Below Lang Canyon Near Livermore
Pine Ck. At Bolinas
Wildcat Ck. At Vale Road At Richmond
Corte Madera Ck. Near Ross
Permanente Ck. Near Monte Vista
Arroyo Valle Near Livermore
Napa R. Near Napa
Napa River Near Saint Helena
West Fork Permanente Ck. Near Monte Vista
Pescadero Ck. Near Pescadero
Arroyo De La Laguna Near Pleasanton
Alameda Ck. Below Welch Ck. Near Sunol
Crow Creek Near Hayward
San Lorenzo Ck. At San Lorenzo
Zone 6 Line B At Warm Springs Boulevard At Fremont
Lagunitas Ck. At Samuel P. Taylor State Park
Walker Ck. Near Marshall
San Gregorio Ck. At San Gregorio
Olema Creek
• 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?
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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
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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
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Which variable is statistically the most significant for the total annual load
predictions?
Unit Annual Peak Discharge Correlated with Unit Sediment Load
And the winner is…
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Unit Annual Peak Discharge Correlated with Unit Sediment Load East Bay
Very Good correlation R2= 0.94
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Unit Annual Peak Discharge Correlated with Unit Sediment Load North Bay
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8Very Good correlation R2= 0.92
Unit Annual Peak Discharge Correlated with Unit Sediment Load San Francisco Peninsula
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Correlation could be improved by low discharge sampling and better understanding of urban watersheds sediment loads
Unit Annual Peak Discharge Correlated with Unit Sediment Load San Francisco Bay
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Other Statistical Correlations
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Unit Annual Peak Discharge Correlated with Unit Sediment Load for Each of the SF Bay Counties
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Other Statistical CorrelationsUnit Annual Peak Discharge Correlated with Unit Sediment Load for Each of the SF
Bay Counties
Other Statistical Correlations #2
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Unit Annual Peak Discharge Correlated with Unit Sediment Load for different types of Geology (classified based on the rock formations resistance to erosion)
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Other Statistical Correlations #2Unit 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
• Each watershed was divided into fife generalized land use classes (based on NLCD data set)– Natural– Agriculture– Low density urban– High density urban– Industrial
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Other Statistical Correlations #2Unit Annual Peak Discharge Correlated with Unit Sediment Load for different land use types
Other Statistical Correlations #238
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Unit Annual Peak Discharge Correlated with Unit Sediment Load for different land use types
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Natural land use type has lower sediment discharge compared with urban land use type
Remaining Work
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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 / acreC percentage of land under construction
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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 Areas3.9 tone / acre/year
Grass Areas0.2 tone / acre/year
Correlate Unit Annual Peak Discharge with Unit Sediment Load for watersheds with land slides or forest firesBoth processes are expected to increase sediment loads at least 30 times compared to the background values
Croplands3.6 tone / acre/year
Questions / CommentsItem #3a
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