Friday, August 31, 2012

The basics of waterbars and wing ditches

The primary pollutant that enters our waterways from forestry operations is sediment.  This sediment comes mostly from roads, skid trails, and firebreaks.  Sediment is carried from overland flow that has gained enough velocity to detach soil particles and carry them with it; this overland flow, if not slowed down and dispersed, ends up in the stream, sediment and all.  One method of slowing down overland flow, as well as dispersing any sediment that it is carrying with it is to construct waterbars in trails, roads, and firebreaks.

Waterbars should be constructed at a 30-45 degree angle, turning overland flow out and away from the road.  

Accompanying a waterbar should be some sort of a turnout, more commonly referred to as a "wing ditch."  As the overland flow is intercepted by the waterbar, it is diverted into the wing ditch and dispersed before it has the opportunity to gain speed and cause further erosion.  It is also important to note that wing ditches should be constructed to be more flat than v-shaped.  This encourages diverted flow to dissipate rather than be concentrated.  

When constructing waterbars it is important to be sure that both ends are tied in to the edge of the road.  This prevents "blow outs" or water from going around the waterbar.  

Waterbars should never be constructed perpendicular to the road, this forms a dam, causing water to stand in the road.  Even though any overland flow has been put to a stop, the integrity of the road has been compromised, due to the 90 degree waterbar with no turnout accompanying it.  

Waterbars and wing ditches should never discharge into streams.  This increases stream bank erosion as well as increases the amount of sediment that enters the stream as a result of operations.

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