Strategies Addressing Hydromodification in Channels Through Unstable Terrains

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Strategies Addressing Hydromodification in
Channels Through Unstable Terrains

• John Gartner
• Barry Hecht
• Shawn Chartrand
• Edward Ballman, P.E.
• BALANCE HYDROLOGICS, INC.

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Field Problem
Incision by streams draining urbanized areas
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Field Problem
Channel dredging, Mowry Slough, Fremont,
California
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Understanding Hydromodification

• Decreased lag time

Erosion threshold??

• Increased peak

• Increased volume

• More frequent erosive flows

• Semi-permanent hydrologic
• change to which the channel
• must adjust

LOGARITHMIC AXIS!
(Leopold, 1968)
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Regulatory context

• Downstream impacts are becoming unacceptable
• CEQA and NEPA
• Endangered Species Act
• County permits per Bay Area RWQCB

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Role of geomorphologist

• Recognize disturbed landscapes and importance as
  sediment sources
• Understand channel form, function
• Comprehend channel adjustments to environmental
  change

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Outline

• Site
• Assessment
• Solutions
• Summary

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Case study Coyote Gulch
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Site

• Ridgetop
• Downstream
• Steep
• Disturbed

560 acres
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Geology

• Orinda Formation
• Tightly folded
• Mass movements
• Beds with varying resistance

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Soils

• Clay Soils
• Low Infiltration
• Millsholm

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Larger watershed context

• Downstream Hydromod
• Biota
• Network
• Barbed

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Flow monitoring and baseline
WY 2004
Discharge (cfs)
Date
Host of info Lag time Calibrate model Seasonal
effect saturation baseflow steps
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Sediment monitoring, baseline
Mostly suspended Regional context Baseline Assess
success
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Stream walks Channel Stability
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• Presentation is continued in
• Gartner GSA talk hydromodification 5-1-05 part
  2.pdf