Urban Drainage and Intersection Design CE 453 Lecture
Urban Drainage and Intersection Design CE 453 Lecture 27 1 Image: http: //www. dhi. dk/Consulting/Water. In. The. City
Urban Street Design - Drainage is a secondary function of an urban street system l 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) l Goals with Drainage on Street l ¡ ¡ ¡ Preserve safety and convenience of traveling public Provide economical means of stormwater transport Prevent water from leaving street system except where appropriate 2
The Stormwater System l Minor system: ¡ ¡ ¡ l 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 3
Intersection Drainage Design - Driveways l Avoid changes in longitudinal drainage due to driveways (ponding, etc. result) l 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 4
Intersection Drainage Design - Intersections l Avoid ponding on approaches – use minimum grades, and avoid sag immediately before intersections (Hazel and 4 th Street) l Locate inlets upstream of intersections (limits flow in intersection) 5
Intersection Drainage Design - Intersections 3. 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 6
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 (not percent!) Z = reciprocal of the cross slope d = depth at the curb in ft. d = [n Q/. 56 Z S 1/2]3/8 See Iowa DOT Design Manual (excellent) 7
Sources: Green Book and SUDAS 8
Typical plan and profile for storm sewer 9
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n. Q 18
Source: SUDAS 19
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