Effects of Urbanization on Watershed Hydrology: The Scaling of Discharge with Drainage Area

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Effects of Urbanization on Watershed Hydrology
The Scaling of Discharge with Drainage Area

• J. C. Galster, F.J. Pazzaglia, B.R.Hargreaves,
  D.P. Morris, S.C.Peters, R.N. Weisman
• Lehigh University
• Geology September, 2006

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Background

• Discharge in a river channel grows as drainage
  basin area increases
• QkAC
• Where
• Q river discharge (m3/s)
• k river base flow (m/s)
• A upstream drainage area (m2)
• c scaling power dependency

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Hypothesis

• Urbanization causes discharge to scale
  nonlinearly because
• Higher percentage of impervious surfaces reduces
  infiltration and drives Hortonian overland flow
• Anthropogenic pathways increase both the volume
  of discharge and the rate of discharge delivery
  to the channel

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Urbanization
http//www.denvergov.org
http//www.burkecentre.org
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Setting

• Similarities
• Drainage area
• Annual precipitation
• Trunk stream channel order
• Relief
• Lack of dams/reservoirs
• Underlying substrate

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Land Use
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Sacony Creek
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Little Lehigh Creek
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Methodology

• Install data logging transducers at various
  stations to record water depth
• Apply a rating curve to calculate river discharge
  with depth
• Record at 15 minute intervals for 5 months
• Identify river base flows and peak events

Galster et al., 2006
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Results
QkAC
For Base Flows Both Sacony Creek and Little
Lehigh Creek c lt 1 For Peak Flows Sacony Creek c
lt 1 Little Lehigh Creek c gt 1
Galster et al., 2006
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Results
For Little Lehigh Creek Peak Flows The
contribution of water from each unit area is not
equal because the downstream urbanized regions
are contribution greater volume per unit area
than upstream forested or rural areas.
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Implications

• Cascading Effects
• Geomorphology-sediment transport erosion drives
  channel incision
• Water quality-
• increased turbidity
• increased contribution of storm water from urban
  areas increases percentage of contamination water
  
• Aquatic ecology-sensitive ecosystems and habitats
  affected
• Human use- larger drainages used as freshwater
  sources