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Road Drainage Alternatives
By
Don Lindsay, CEG, PE Engineering Geologist/Civil Engineer
California Geological Survey
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“Three of the mostimportant aspects of road
design – drainage, drainage, and drainage!”
Keller and Sherar, 2003
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ImpactsImpacts
Roads can alter both drainage patterns and runoff generation, resulting in:
• Destabilization of side-cast material downslope hillsides;
• Gullying and channel network expansion;• Increased downstream sediment loads;• Altered stream flow and channel adjustments;• Standing water (pothole, sag, rut, wet area)
can weaken the subgrade and accelerate erosion and damage to the road.
See Drew Coe’s and Mike Wopat’s presentations under Series 1
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Photo: Matt Boone, RWQCB
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Photo: USDA Forest Service
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Photo: USDA Forest Service
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Photo: Gordon Keller
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Primary Objective
Design, construct and maintain roads so they are hydraulically invisible (i.e., water intercepted by roads is returned to natural flow processes as quickly as practical).
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Remember!
Successfully treating road drainage
= (hydraulically invisible)
Protecting natural
+ resources
Ensuring full use of road and reduced maintenance and repair costs
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OutlineOutline
■■ Types of road prismTypes of road prism shapesshapes
■■ DrainageDrainage structuresstructures• TypesTypes• SpacingSpacing• LocationLocation
■■ Ditch and outlet scourDitch and outlet scour protectionprotection
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Road Prism Shapes
Keller and Sherar, 2003
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Photo: Gordon Keller
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Photo: Gordon Keller
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Photo: Matt Boone, RWQCB
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Photo: Matt Boone, RWQCB
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Drainage Structure
■■ Inboard Ditches
■■ Culverts (Cross- drains)
■■ Rolling Dips■■ Waterbars
■■ Over-side drains/flumes
■■ Leadouts/ditchouts
■■ Subdrains• Intercept• Blanket
■■ Others• Rubber water
diverters• Open-topped
channels• Grade
Reversals and Rolls
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Ditch Structures
Photo: USDA Forest Service
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Ditch Structures
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Ditch Structures
Photo: Gordon Keller
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Pipe Structures
Keller and Sherar, 2003
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Pipe Structures
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Pipe Structures
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Waterbars
Keller and Sherar, 2003
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Rolling Dips
Keller and Sherar, 2003
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Dips
Photo: Gordon Keller
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Over-side drains
Photo: Gordon Keller
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Over-side drains
Photo: Matt Boone, RWQCB
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Over-side drains
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Leadouts
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Subdrains
Photo: Gordon Keller
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underdrain
Keller and Sherar, 2003
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Blanket drain
Keller and Sherar, 2003
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Blanket drain
Keller and Sherar, 2003
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Geofabric
NONWOVENNONWOVEN WOVENWOVEN
High porosity +High porosity + HighHigh
permeabilitypermeability
= High flow for= High flow for longer.longer.
HighHigh permeability butpermeability but
percent openpercent open area (POA) isarea (POA) is more prone tomore prone to
clogging.clogging.
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Rubber diverters
Photo: Gordon Keller
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Open-topped channels
Photo: Gordon Keller
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Grade reversals/Rolls
Source: Gordon Keller
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Questions?
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Drainage StructureDrainage Structure SpacingSpacing
■■ Drainage structures should be constructed at aDrainage structures should be constructed at a spacing that would prevent excessive erosion spacing that would prevent excessive erosion either in the inboard ditch, along the road either in the inboard ditch, along the road surface, or downslope of thesurface, or downslope of the road.road.
■■ Spacing is a functionSpacing is a function of:of:• RoadRoad gradegrade• HydrologyHydrology• SoilSoil typetype• SurfacingSurfacing
■■ Modify Structure locations to account for Modify Structure locations to account for landscape features as necessary (topography,landscape features as necessary (topography, wet areas, landslides,wet areas, landslides, etc).etc).
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Erosion power = Kinetic energy = 0.5(mv^2)
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Spacing is a function of:•Road grade•Hydrology•Soil type•Surfacing
Copstead, R. L., et al. (1998)
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Drainage Structure Location1. Spaced close enough to avoid excessive rilling and gullying.2. Located sufficiently upgrade of watercourse crossings
to allow filtering of sediment-rich runoff by the buffer strip between the road and stream.
3. Direct discharge away from unstable or potentially unstable areas.
4. Upgradient of drainage divides to keep water from one catchment basin mixing with, and potentially impacting, another catchment basin not conditioned to the additional flows.
5. Discharge onto divergent (convex) to planar slopes, where possible, to promote better dispersion and infiltration.
6. Drain saturated soils of the road prism.7. Upgrade of breaks in the road grade that transition from
low-gradient to high-gradient.
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Place upgrade of stream crossings to allow for filtering of sediment-rich runoff prior to entering the stream.
Oregon Department of Forestry
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Place to discharge away from unstable or potentially unstable areas.
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Place upgrade of drainage divides to prevent water from one catchment basin mixing with, and potentially impacting, another catchment basin not conditioned to the additional flows.
50Oregon Forest Resources Institute, 2002
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Place to discharge onto divergent (convex) to planar slopes, where possible, to promote better dispersion and infiltration.
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Place to drain saturated soils present in the road prism.
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Place upgrade of changes in the road grade from low- gradient to high- Place upgrade of changes in the road grade from low- gradient to high- gradient.gradient.
Oregon Forest Resources Institute, 2002
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Energy Dissipators
The use and selection of an appropriate energy dissipator should be based on in-field conditions that include:
■ Flow■ Soil erodibility■ Slope gradient, and■ Slope roughness and cover
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Ditches
Photo: Gordon Keller
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Photo: Gordon Keller
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Photo: Gordon Keller
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Outlets
Photo: Gordon Keller
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Stilling basin / tailwater
Figure: Brian McNoldy
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Dip outlets
Photo: Matt Boone, RWQCB
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Photo: Matt Boone, RWQCB
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Copstead, R. L., et al. (1998)
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Remember!
Successfully treating road
= drainage
Protecting natural
+ resources
Ensuring full use of road and reduced maintenance and repair costs
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Questions?
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