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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