1 Urban Drainage and Intersection Design Image:

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Urban Drainage Urban Drainage and Intersection and Intersection

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Urban Drainage Urban Drainage and Intersection and Intersection

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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)

8Sources: Green Book and SUDAS

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Typical plan and profile for storm sewer

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nQ

19Source: SUDAShttp://www.iowasudas.org/documents/Ch2Sect5-05.pdf

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