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Water flows across, not down the track so it does not erode
Solution for water erosion
reduce longitudinal track grades to less than 6; the tracks will be longer but environmental impacts and ongoing maintenance will be reduced
ensure that water drains across the track by establishing and maintaining a 6 transverse fall; sometimes it may be necessary to develop adequate earth drains that intercept and direct runoff downhill
avoid use of erosion bars even disguised as steps; they delay the inevitable and give rise to cascades and other erosion problems
better to reroute and encourage nature to restore
  ... in these places, erosion of tracks is unacceptable ...