A berm is a low embankment, typically found on the outside edge of a road or landing, and often used in steeper, erosion-prone terrain. They are constructed to channel stormwater away from vulnerable areas to cut-outs, and act as an additional erosion and sediment control measure. Berms can reduce erosion from surface scouring or fill failures. Berms can be used to channel water from erosion-prone fill slopes and old slip faces onto hard and stable ground via additional water control structures, like cut-outs or flumes, or to direct water to sediment control structures, like through slash, sediment traps and ponds or silt fences.
Build berms at the time of road or landing construction. Use an excavator to construct and compact the berm fill. Where berms are to be constructed, the roadway width needs to be slightly wider to contain the berm footprint. Ensure the fill slope has not been over steepened by the berm. Fills that are too steep are more prone to failure if the natural angle of repose of the soil has been exceeded. Do not use berms to store excess fill. Build berms only as wide as required, as adding a berm will increase the load on the outside road edge and may create additional instability in highly erodible soils (exceed shear strength). If necessary, it is recommended to grass or hydroseed berms to protect them in sensitive areas. Where practicable, avoid spraying vegetation on the berm when doing a pre-plant, desiccation spraying. Consider armouring berms where cut-out spacing is restricted by the terrain, or cannot easily be addressed with flumes or drainage socks.