Urban Drainage and Intersection Design

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Urban Drainage and Intersection Design

• CE 453 Lecture 27

Image http//www.dhi.dk/Consulting/WaterInTheCity
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Urban Street Design - Drainage

• Drainage is a secondary function of an urban
  street system
• Runoff in areas is actually brought to the street
  and the gutter (versus water either being
  intercepted or brought to the ditch in rural
  areas)
• Goals with Drainage on Street
• Preserve safety and convenience of traveling
  public
• Provide economical means of stormwater transport
• Prevent water from leaving street system except
  where appropriate

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The Stormwater System

• Minor system
• Role collect stormwater and discharge to major
  system
• Design Storm (return period) 2 to 10 years
  typically (some use 25-year)
• Use inlets and conduits (small stuff - most of
  the system)
• Major system
• Role carry stormwater from minor system to
  natural watercourses
• Design storm typically 100-year
• Use culverts, bridges, retention basins
  (detention basins?) big stuff
• If fails, property damage or loss of life

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Intersection Drainage Design - Driveways

• Avoid changes in longitudinal drainage due to
  driveways (ponding, etc. result)
• Prevent water entering driveway by
• High point of drive should exceed maximum inside
  curb line (top of curb for arterials/collectors
  and 4 inches over curb for locals)
• Grade land to flow into roadway

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Intersection Drainage Design - Intersections

• Avoid ponding on approaches use minimum grades,
  and avoid sag immediately before intersections
  (Hazel and 4th Street)
• Locate inlets upstream of intersections (limits
  flow in intersection)

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Intersection Drainage Design - Intersections

• Consider impact on drainage due to intersection
  cross slope adjustments (for smooth travel)
  alternatives
• Adjust minor street only (for local/collector and
  collector/arterial)
• Adjust gutter line of both streets (only
  appropriate if intersection area is small
  local/collector)
• Adjust both centerlines but maintain cross
  section of both generally avoid

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Calculations

• Given Q, find d (depth) and T (width) of flow
•  
• Use Q0.557(Z/n)S1/2 d8/3
• where S longitudinal grade in ft/ft (not
  percent!)
• Z reciprocal of the cross slope
• d depth at the curb in ft.
•  
• d n Q/.56Z S1/23/8
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• See Iowa DOT Design Manual

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Sources Green Book and SUDAS
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Typical plan and profile for storm sewer
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Source SUDAS
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