Transcript Construction of Water Bars and Turn-Outs

Construction of Water Bars and
Turn-Outs
2005, Mid Star Timber Harvesting, Inc.
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Purpose
This course has been designed to ensure all
equipment operators who work in forestry
operations have the knowledge and skills
necessary to properly and consistently
construct, maintain, and repair water bars and
turn-outs in accordance with Best Management
Practices for Forestry.
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Course Objectives
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Demonstrate correct size, distances between,
and angle of construction for water bars
Demonstrate correct size, distances between,
angle of construction, and outfall design for
turn-outs
Learn step-by-step procedures for constructing a
water bar/turn-out system.
Consider alternative construction techniques for
water bars and turn-outs when faced with nonroutine situations
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The Erosive Effects of Moving Water
The purpose of water bars and turn-outs is to prevent
erosion of the road surface and ditches by forcing water to
leave the road bed and enter the forest floor.
As water moves down-grade, it picks up soil and carries it
away, resulting in erosion. The farther the water is allowed
to travel down the road bed, the more velocity it will gain.
If the distance the water is allowed to travel is not
somehow shortened, the increasing velocity of the water
can result in increased erosion of the road bed and an
undesirable amount of silt being carried to the forest floor
when the water finally reaches a point of discharge from
the road bed.
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Water Bar Design Considerations
Water bars must be designed so that water is not
allowed to travel great distances down the road bed
before being discharged and should in most cases be
constructed so that the road bed may still be used by
light truck traffic.
By constructing water bars of a sufficient height,
width, angle from the road edge, and distance
between them, erosion control objectives can be met
while maintaining aesthetic qualities that are pleasing
to forest road owners and users.
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Water Bar Construction Time
To properly construct water bars takes time.
A good rule of thumb to use when
constructing water bars is to allow thirty
minutes for each water bar constructed on an
average road bed twenty-four feet wide.
Patience during construction will ensure the
water bar will continue to function properly for
years to come.
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Water Bar Size
Water bars should reach all the way across the
road, be approximately 12 feet wide at the
base, and 2 feet high from the uphill trough to
the crest.
12’
2’
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Distance Between Water Bars
The table below shows recommended distances
between adjacent water bars depending on the slope
of the road.
Slope
Distance
3%
200’
5%
135’
10%
80’
15%
20’
20%
45’
30%
35’
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Distance Between Water Bars
Instead of having to remember the slope to distance
relationship shown in the previous table, a good rule of
thumb is to use the method shown below.
Standing at the crest (or trough) of the lower water
bar, the crest (or trough) of the next water bar uphill
should be at approximately eye level.
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Angle of Construction for Water Bars
Water bars should be constructed at approximately 30
degrees to the direction of travel on the road. This angle
will allow the water to flow off the surface of the road
with little or no obstruction in flow.
Although ideally there will be minimal silt carried in the
water diverted by a properly constructed water bar, during
heavy rainfall, as water reaches a water bar built directly
across the road, it tends to resist an abrupt change in
direction of flow and will either jump the water bar or
deposit excess silt in the trough during the change in
direction and velocity…..
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Angle of Construction for Water Bars
Over time, excess silt deposited in the trough can
reduce the working height of the water bar and render
it ineffective.
By building the water bar at an angle, the water
retains enough of it’s initial velocity to keep the
trough cleaned out and the water bar will remain
effective over a longer period of time.
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Angle of Construction for Water Bars
A rule of thumb for achieving the correct angle of a
water bar is shown below.
Step off the distance from the beginning of where
you want the water bar on one side of the road
straight across to the other side. Divide that distance
by three and step the resulting distance downhill to
find the ending point of the water bar.
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Turn-Outs
It goes without saying that water bars would
be completely ineffective without a means for
water to exit the road. Turn-outs are used at
every water bar and as needed along the road
to allow water an escape to the forest floor.
The proper construction of turn-outs is as
important as water bars to prevent erosion and
excessive siltation of the forest floor.
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Turn-Out Size
The size of turn-outs should be at least as wide
at the entrance to the turn-out as the width of
the water bar or ditch that feeds water into it.
This prevents any bottleneck in the flow of
water from the water bar or ditch to the turnout. The turn-out should then broaden and
flatten out as it continues onto the forest floor.
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Distance Between Turn-Outs
Turn-outs should be placed at the exit side of
every water bar and at every opportunity along
the road.
The bottom line is this:
You really can’t have too much road drainage.
Install turn-outs as often as possible along the
road on each side to carry water off the
traveling surface of the road.
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Distance Between Turn-Outs
The following table shows some guidelines for distances
between turn-out installations based on the slope of the
road.
Slope
Distance
3%
235’
5%
180’
10%
140’
15%
125’
Remember, in most cases, you can’t have too much
drainage!
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Angle of Construction for Turn-Outs
Turn-outs should be built at the same angle as the
water bar that feeds it.
In the case of a stand-alone turn-out, it should
gradually curve away from the road toward the
forest floor, but in no case should the outfall be
greater than 90 degrees from the direction of
travel on the road.
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Angle of Construction for Turn-Outs
Right
Wrong
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Outfall Design for Turn-Outs
The outfall section of a turn-out should be flat
and about a dozer blade wide, if possible.
There should be no obstruction to prevent
water from flowing freely out of the outfall.
Standing water in a turn-out after a rain is an
indication of an improperly constructed one.
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Water Bar/Turn-Out Construction
Step 1
Determine the landowner/customer’s objectives.
Some want a more thorough job than others based
on financial or time constraints.
Some may want water bars built not only to
prevent erosion, but also to prevent access. In this
case, the water bars should be built higher and
steeper than normal.
A clear understanding beforehand can prevent
most dissatisfaction with jobs after completion.
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Water Bar/Turn-Out Construction
Step 2
Assess the terrain and soil type and develop a plan.
Based on terrain and soil type observations,
decisions can be made on water bar and turn-out
placement and frequency. Sandy soils need more
frequent water bars and turn-outs than rocky ones.
Make a note of any stream crossings or streamside
management zones in your planned work zone.
These require special treatment in order to avoid
water quality violations.
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Water Bar/Turn-Out Construction
Step 3
Remove any organic debris (leaves, straw, grass,
sticks) from the surface of the road in the areas
around where water bars are to be constructed. This
debris, if mixed in with the soil used to construct a
water bar, will not allow the soil to become cohesive
and stabilize.
Also, remove any organic debris from the area where
the turn-out leading out of a water bar is to be
constructed. If at all possible, soil from the turn-out
area should be brought back into the road and used in
the construction of the water bar.
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Water Bar/Turn-Out Construction
Step 4
Step off or visualize the correct angle and size of
construction.
Gather the soil into a pile shaped slightly larger
than you think you will need for the finished water
bar. The lowest part of the trough should be cut out
of natural ground, if possible.
Pack the entire pile by walking back and forth over
it with your machine (dozer, skidder, etc.).
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Water Bar/Turn-Out Construction
Step 5
Finish shaping the pile with the blade of your
machine. If the road is to be used while the water
bars are in place, this step is crucial to the aesthetic
quality of the job. Any excess material bladed off the
uphill side of the water bar should be placed on the
downhill side. Using a dozer, you should be able to
blade all the way over the water bar, keeping the
blade in contact with the ground. If not, the crest of
the water bar is probably too sharp.
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Water Bar/Turn-Out Construction
Step 6
If you were able to use dirt for the water bar from the
turn-out area, complete construction of the system by
finish grading the turn-out at the exit side of the
water bar.
The turn-out should slope downhill from the water
bar at about the same rate of slope as the water bar
that feeds it.
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Non-Routine Situations
Inevitably situations will arise where these
guidelines for water bars and turn-outs will not be
practicable. When faced with those situations, you
should study carefully any possibilities and options
available. The most important thing to remember is
the reason you are building water bars and turn-outs
on the road to begin with:
ELIMINATE OR REDUCE THE POSSIBILTY OF
EROSION!
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