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Urban Drainage Urban Drainage and Intersection and Intersection
DesignDesign
Urban Drainage Urban Drainage and Intersection and Intersection
DesignDesign
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 – 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 flow (top of curb for arterials/collectors and 0.1 m over curb for locals)
– Contour 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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• 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
Intersection Drainage Design - Intersections
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CalculationsGiven Q, find d (depth) and T (width) of flow Use Q=0.557(Z/n)S1/2 d8/3 where: S = longitudinal grade in ft/ftZ = reciprocal of the cross slope d = depth at the curb in ft. d = [n Q/.56Z S1/2]3/8
See Iowa DOT Design Manual (excellent)
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8Sources: Green Book and SUDAS
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Typical plan and profile for storm sewer
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nQ
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19Source: SUDAShttp://www.iowasudas.org/documents/Ch2Sect5-05.pdf
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