142 



(a) Spacing requirements - spacing depends on a number of factors 

 such as road grade, and type of material. Guides for spacing 

 are presented in Megahan (1977). 



(b) Open-top culverts are usually constructed of wood. They 

 should be installed at a 30O angle downslope to promote 

 self cleaning and make crossing easier. Culverts of this 

 type must be properly maintained to prevent plugging and 

 damage by traffic. 



(c) Intercepting dips, when properly constructed, are cheaper to 

 maintain and more permanent than wood, open-top culverts. 



Dip design depends on the kind and speed of the traffic using 

 the road. Dip designs allow road use by passenger autos 

 travelling at speeds of approximately 30 kilometers per hour. 

 On steeper roads it may be necessary to install open-top 

 culverts (using the same design) in addition to dips to 

 meet the cross-drainage spacing criteria. 



(d) In addition to cross drain spacing, location of cross drains 

 is an important factor to consider in minimizing sediment 

 delivery to stream channels from either ins loped or out- 

 sloped roads. 



23. Berms are required on the outside edge of the road at specific 



locations where alignment and grade characteristics cause excessive 

 runoff from the road tread over the fill slope. Use compacted 

 soil, soil cement, or asphalt mixtures to construct stable berms. 

 Where necessary, use downspouts in the berm to safely carry water 

 to the bottom of the fill slope. Locate downspouts at safe water 

 discharge points and provide energy dissipators (rock basins, etc.) 

 to further recuce erosion hazards. 



