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Roads,
Skid Trails, Landings, and Stream Crossings |
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Surface
Drainage |
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There are a number of features that can be built
during road construction to contend with the issue of surface drainage.
Three of the most commonly used features are the rolling dip, the spreader
ditch and a cross culvert. |
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Rolling
Dip |
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A rolling dip is much like a hump constructed
in the road bed itself. The purpose is to divert any water from the road
surface or the inside ditch off the road into the adjacent terrain. The
rolling dip is constructed at a gentle angle to the direction of the road
so the dip may be easily traveled. The bottom of the dip is sloped to the
outside to carry water away from the road. The dip should be 120º to
140º to the direction of travel.
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(right) A well-constructed rolling dip. |
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Spreader Ditch |
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A spreader ditch diverts water from the road onto an adjacent
area where vegetation, a decrease in velocity or the spreading out of the
stream of water will allow the sediment to settle out and the water to be
absorbed into the ground. The spreader ditch can be successfully used wherever
excessive amounts of water may collect on the road surface or in drainage
ditches. The spreader ditch works particularly well when used in conjuction
with a rolling dip. But it can work equally well with an inside ditch or
cross culvert. |
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(left) An effective spreader ditch. |
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Cross Culvert |
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During road construction, a cross culvert should be installed
to drain water from either the inside ditch or from natural water sources
such as seeps or small springs uncovered by road excavation. These culverts
are used to transport
water to areas where infiltration can occur or the natural flow will be
resumed. Rolling dips, spreader ditches or cross culverts can each be used
to suit a specific situation on any particular road. The combination of
two or more are even
more effective to control the movement of water away from the road surface,
cut slopes and fill embankments. Other features of more limited utililty
can be used. Some of these are the open-top culverts, water bars and box
or log culverts. |
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When ditches are used with insloped
roads, drain runoff through culverts or
into adjacent vegetation to filter sediment.
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This properly constructed outfall is
armored and located close to fill material. |
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Don't construct outfall so it is elevated above fill material.
The fall gives water additional energy that accelerates erosion. |
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