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Planning & Design
Improve Soil Health
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Contour Grading and Slope Rounding
Images above illustrate slope rounding and contour grading proposed for Route 46 San Luis Obispo County between postmile 32.2 and 56.3
What is This Treatment?
Contour grading and slope rounding involves grading the project roadside with smooth, flowing contours that help integrate highway improvement within its surrounding environment. Concentrated water flows in graded valleys helps sustain vegetation in arid regions.
Besides helping make a highway facility compatible with its surroundings, this grading technique also helps reduce erosion and maintain water quality by breaking the slope into many smaller tributary areas dispersing runoff. Due to their higher moisture content, these focused drainage areas are better suited to supporting larger plants such as trees and shrubs than the planar slopes produced by rectilinear grading.
Landform Grading/Contour Grading Training Video
When to Use This Treatment?
- Consider using contour grading and slope rounding whenever permitted by the right of way limits.
- Typically used on cut slopes 2:1 and 3:1 (H:V) composed of rippable material. For specific maximum slope gradients, consult your geotechnical engineer.
- Comply with the guidance provided in the Highway Design Manual (HDM) Chapter 300, Topic 304.4 Contour Grading and Slope Rounding.
- Comply with the guidance for Slope Roughening/Terracing/Rounding/Stepping provided in Appendix A of the Caltrans Storm Water Quality Handbooks Project Planning and Design Guide.
Consider Using With:
- SSP 20-170 Local Topsoil
- SSP 20-040 Erosion Control (Hydroseed)
- SSP 20-055 Erosion Control (Compost Blanket)
Reduced stormwater runoff volume and velocity.
Improved infiltration rate.
Improved soil water holding capacity within sculpted valleys.
Improved potential for vigorous long term vegetation coverage.
- Topographic diversity supports a wider range of plant material.
- Reduces irrigation requirements by providing sheltered areas with higher moisture content that can be planted with higher moisture loving plant material such as trees and shrubs.
- Provides visual compatibility between highway facilities and their surrounding environment.
May increase the cost of earthwork activities.
Requires site accessibility by earthwork equipment.
- Use standard department Earthwork specifications.
Plans and Details:
- No Standard Plans or Details available.
- No pricing information is currently available for contour grading.
- Highway Design Manual (HDM) Chapter 300, Topic 304.4
- Caltrans Contour Grading Slope Rounding Webinar
- Schor, H. & Gray, D., 2007. “Landforming: An Environmental Approach to Hillside Development, Mine Reclamation and Watershed Restoration.” Published by John Wiley & Sons, Inc.