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Analogy Between Rivers and Human Personality

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S. Fork Nooksack River , WA Reasons for Land Clearing Agriculture Lumber Mining Urban Development Assessing Impacts on Channel Morphology Assessing Impacts on Channel ... – PowerPoint PPT presentation

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Title: Analogy Between Rivers and Human Personality


1
S. Fork Nooksack River , WA
2
Reasons for Land Clearing
  • Agriculture
  • Lumber
  • Mining
  • Urban Development

3
Impacts of Land Clearance
- Cross section of a graded stream in equilibrium
  • Land clearance for agriculture and lumber
    removes forest vegetation and exposes soil
  • What happens?

4
Sediment Load vs. Discharge
From Leopold et al. (1964) Rio Grande River
near Bernalillo, N.M.
G pQj where G is suspended load and j is
between 2 and 3
5
Assessing Impacts on Channel Morphology
Parameter Upstream At site
Downstream Velocity Discharge Roughness Slope Area
Load
6
- Sediment load increases at an exponentially
greater rate than discharge causing deposition
- Decrease in sediment supply with reforestation
will result in incision and return to prior river
level but with higher river banks
  • Deposition resulting from deforestation causes
    increase in slope capable of transporting the
    higher sediment load, thus bringing the system
    back into equilibrium slow process (102-103
    years)
  • Reforestation decreases load and so incision
    relaxes the higher slope created by earlier
    aggradation faster (101-102 years)

7
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8
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9
Lower Poultney River, VT
10
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11
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12
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13
Merrimack River, NH
14
Impacts of Urbanization
- Cross section of a graded stream in equilibrium
  • Housing development clears vegetation and paves
    surface
  • What happens?

15
Courtesy of VT DEC River Management
16
Assessing Impacts on Channel Morphology
Parameter Upstream At site
Downstream Velocity Discharge Roughness Slope Area
Load
17
Impacts of Urbanization
- Increased discharge causes erosion
- Tendency is for incision in clay
- And channel widening in sand
- Both decreasing slope due to incision and
increasing channel area due to widening decrease
the capacity, bringing the system back into
equilibrium with the increased discharge
18
Effect of Urbanization on Flood Hydrographs
19
Channel Incision Near Santa Fe, New Mexico
Control Sections
Urbanized Sections
From Dunne and Leopold (1978)
20
Increased Discharge Results From
  • Greater percentage of impervious surface
  • Filling of wetlands
  • Reconfiguration of drainage network
  • Smoothing of land surface
  • Loss of floodplain storage

21
Hydrologic Changes Resulting From Urbanization
From MacBroom (1998)
22
Effect of Wetlands on Peak Runoff
Percentage of Watershed Covered by
Wetlands 0.0 0.2 1.0 3.0 5.0
Peak Flow Reduction Factor 1.00 0.97 0.87 0.75 0.7
2
From MacBroom (1998)
- A watershed with 3 wetlands can have peak
flows 25 smaller than a similar watershed
without wetlands
23
Loss of Floodplain Storage
From MacBroom (1998)
24
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25
From Gould (1975)
26
From Gould (1975)
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