1. 1 Urban Drainage and Intersection Design Image: http://www.dhi.dk/Consulting/WaterInTheCity

2. 2 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

3. 3 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

4. 4 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

5. 5 Intersection Drainage Design - Intersections Avoid ponding on approaches – use minimum grades, and avoid sag immediately before intersections (Hazel and 4 th Street) Locate inlets upstream of intersections (limits flow in intersection)

6. 6 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

7. 7 Calculations Given Q, find d (depth) and T (width) of flow Use Q=0.557(Z/n)S 1/2 d 8/3 where: S = longitudinal grade in ft/ft Z = reciprocal of the cross slope d = depth at the curb in ft. d = [n Q/.56Z S 1/2 ] 3/8 See Iowa DOT Design Manual (excellent)

8. 8 Sources: Green Book and SUDAS

9. 9 Typical plan and profile for storm sewer

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18. 18 nQ

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

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