Janet M' Sowers and Justin T' Pearce

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Historical Geomorphology of the Santa Clara
basin, California

• Janet M. Sowers and Justin T. Pearce
• William Lettis Associates, Inc.
• Research supported by
• Santa Clara Valley Water District
• Oakland Museum of California
• CALFED

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• What were the streams of the Santa Clara basin
  like two hundred years ago?

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Land Cover, 2003 Santa Clara Valley
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Map series published by the Oakland Museum
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Primary sources of historical information

• 1939 aerial photography
• 1890's 15-min USGS topographic maps
• 1876 Historical Atlas of Santa Clara County
• 1998 EcoAtlas
• 1958 Soil Survey

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Modern Waterscape of the Santa Clara Basin
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Modern Waterscape of the Santa Clara Basin
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Historical Waterscape of the Santa Clara Basin
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Active alluvial fan systems
Distributary system Multiple unstable channels
sediment deposited as lobes.
Levee system Single stable channel sediment
deposited as levees.
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• Historical Waterscape of the
• Santa Clara Basin

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Schematic Stream Profile
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In downstream direction

• Erosion Deposition
• Gradient
• Channel depth
• Discharge

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Quaternary Geology
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• 1899 USGS

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1953 USGS
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1939 Air Photo
1939 Air photo
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Creek Watershed Map of Central San Jose
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San Francisquito Creek
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San Francisquito Creek Fan
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Natural Levees
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Historical Waterscape of the Santa Clara Basin
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Conclusions

• Original system an intimate interaction among
  surface water, groundwater, sediment, and biota.
• Valley floor topography reflects coalescing and
  competing alluvial fans and levees.
• Reaches classified by function and character, A
  B C D.
• Most SC basin streams are artificially connected
  to bay, designed for storm water conveyance.
• 5. Map tool is now available that provides
  historical and modern context for restoration
  planning