from a siphon to deflect weeds and debris into the wasteway during
chaining operations, as shown in Figure 178.

Fig. 178

Short vertical boards on the upstream face of the boom, Figure 179,
extend below the water surface a nominal distance to prevent float-
ing material from being drawn under the boom. Logs may be sub-
stituted for the horizontal members of the boom and the length of the
boom varied to fit the given canal or lateral. Although not designed
as a platform from which to operate, the boom could be made so by
providing a decking.

pe 2"x4" Ties-~~__ 76 x6" Timbers-.

ee Za c
HY ANN

i INA

“s--2" Facing—-~

1
1
1

7
———S

>
2'-0'

I
bena-——

Fig. 179

151


boom consists of a
25-foot section of
6-inch-diameter
irrigation tubing
plus 8 feet of 3/4-
inch electrical
conduit.

Figure 167 illustrates
the burning of weeds
which were blown

into the channel by the
wind, In Figure 168,
inplace dry weeds

are being burned.

P22 2-OSPBa,

Figure 169 shows
a hand propane
Fig. 169 burner in use on the
Columbia Basin
Project. The burner
is being used to burn scattered groups of weeds on a small lateral.

Weed Traps
Wire Weed Traps

An inexpensive and simple weed trap to collect weeds and debris in
an irrigation canal can be constructed of smooth wires placed at an
angle to the waterflow which diverts floating material into a pocket
or trap along the banks as shown in Figures 170 and171. This weed
trap was designed and constructed by personnel on the Tucumcari
Project, Tucumcari, New Mexico.

The weeds are guided into the trap by smooth No. 9 galvanized wires
which are strung 4 inches apart across the ditch at an angle of not
greater than 20° to the embankment. The wires are placed parallel
in a vertical plane from a few inches above the water level to about
half the depth of the canal. Bracing with guy lines is suggested to
prevent bending of the 2-inch pipe uprights and to keep the wires
tight.

The trap or pocket, constructed of woven wire, may be of any width
and may be extended for some distance parallel to the ditchbank.
Debris is removed from the trap by using a weed fork mounted upon
a mobile crane. In this manner the accumulated weeds are removed
quickly at a fraction of the expense of hand labor.

145


Fig. 184

The close spacing of the longitudinal bars of the rack probably con-
tributed to the problem, though the rack is necessary if the trash,
etc., are to be kept from the pumps.

To overcome the problem, the irrigation district installed electri-
cally powered angle-iron drags, attached to endless link chains.
These were operated from sprocket-driven pulleys on both sides of
the rack. To date, the device has proved very satisfactory in
removing weeds and debris from the rack and with additional modi-
fication proposed will be even more efficient in operation.

Many of the ideas incorporated in the Amon siphon rack cleaning
device were taken from a similar installation made to protect and
clean another trashrack at the Grandview Irrigation District Pump-
ing Plant on the Yakima Project. The Amon installation, as shown
in the drawing, Figure 186, consists of a rigid steel frame support-
ing a lengthened standard Bureau trashrack, which is cleaned by
3-1/2- by 3-1/2-inch angles connected on each end‘to moving chains.
The cleaning angles move about 5 feet per minute. Prior to the
installation of the device, the trashrack was remodeled so that the
rack and cleaning device frame now rests ona 1-1/2:1 slope.

As shown in Figure 187, a 1/4-horsepower motor provides the

power through a stoker gearbox and a 1-3/4-inch steel shaft at the
top of the rack. The upper bearings are connected to the frame in
such a manner that they are adjustable to allow taking slack out of

155


A somewhat similar chaining device to that previously shown is that
shown in Figure 157 and used by the Twin Falls Canal Company,

Idaho.

from smaller canals and laterals.

This boom and chain are used in the removal of pondweeds

F48-100-80

Fig. 158

A cylinder for
demossing laterals
and drain ditches and
for loosening silt
deposits is shown in
Figures 158 and 159,
This device, known as
"Ganow's Pondweed
Cutter,'' was developed
by the Gem Irrigation
District in its shops
at Homedale, Idaho,

The rotary action

of the device as it

is pulled forward

cuts the pondweeds
and sandbars from the
bottom of the laterals,

The cylinder is
54 inches in diameter,


Trashracks

Trashrack for Canals and Larger Laterals

The trashrack shown in Figure 180 is of the type presently in use on
laterals in the West Canal area of the Columbia Basin Project,
Washington. The flat slope of the rack aids in the removal of weeds
and the landing mat deck provides good footing for removal of the
accumulated debris. The trashrack shown was installed in a lateral
having a capacity of 400 cubic feet per second.

Surplus rails are used for the supporting crossmembers of the trash-
rack and heavy-duty pipe for the rack varies from 3/4 to 1-1/4 inches,
depending on the length of span. The rack shown was constructed of
1-1/4-inch pipe with the longest pipe length being about 20 feet.

The pipe is spaced 8-inch center to center and placed on a slope no
steeper than 4:1. Upper ends of the pipes are loosely attached to
the rail by large spikes which pass through holes in the ends of the
pipes and through the web of the rail. The foundation for the rail
crossmember can be of concreteor serviceable timber. The plat-
form required in large laterals, as shown, has a deck constructed
from surplus landing mat supported by a pipe framework.

In many cases the complete unit is fabricated in the project shop
and is rigidly constructed, using pipe or heavy strap around the
outside perimeter of the rack. A fence enclosure is constructed
adjacent to large installations for deposition and burning of weeds
collected.



Fig. 187

the chain. The lower sprockets are attached to the frame through
hardwood bearings. These are highly recommended.

Those responsible for operation and maintenance of the trashracks
believe the automatic cleaning device can be improved by extending
the trashrack 3 to 6 feet above the operating deck. Sometimes, the
flap gate which permits passage of the cleaning angles at the bottom
of the canal becomes too heavy to be lifted when the screen is par-
tially plugged with debris. This can occur particularly when the
device has not been in operation for a period of time. Shortening
the flap gate would improve this condition. It is also believed the
spacing between the cleaning angles should not be more than 5 feet.

Cost of remodeling the structure and installation of the device was
$2,100.

Several other views of the device with appropriate captions are

shown in Figure 188. The 2-foot flap gate, at the canal bottom,
allows for passage of the cleaning angles.

158


Fig. 183

Self-cleaning Weed Rack

The Kennewick Division of the Yakima Project, Washington, has
about the same floating debris problems experienced elsewhere.
Devices in use include, among others, the weed traps and sloping-
pipe weed racks. However, the most troublesome spot on the canal
is a siphon entrance which is also the entrance to a direct-connected
turbine pump.

The Amon siphon and pump entrance, at Mile 25 on the main canal
(243 cubic feét per second) was originally equipped with a trashrack
set on a 1:1 slope, with l-inch openings. With this rack absolutely
clean, the average velocity through the 1-inch slots approached

5 feet per second. Algae, tumbleweeds, and other debris floating
in the canal increase operation and maintenance problems at this
structure. To reduce the problems, the automatic weed rack shown
in Figure 184 was installed.

Angle-iron bars moving upward by sprocket-driven endless chains,
carry weeds to a conveyor which in turn carry the weeds to a pit
which is provided to trap and burn the weeds.

The trashrack shown in detail on the drawing, Figure 185, was
installed during original construction of the canal and plant facili-
ties. The rack was installed on a 1:1 slope and had 1-inch clear
openings between longitudinal bars which were supported by cross-
members at 4-inch centers. It was difficult and time consuming

to prevent obstruction of the trashrack by weeds, moss, and debris.

154



Similar in many

respects to the
. diversion-type weed
trap previously
described is that
shown in Figures
174 and 175. The
essential difference
is that a channel has
been excavated at the
far end of the trap
into which the weeds
are diverted and
from which they can
then be removed
without seriously
interferring with
the flow of water
in the canal.

Fig. 174 The diversion struc-
ture and bypass
channel on the West
Canal of the Columbia
Basin Project is
shown in Figure 174.

Figure 175 shows
the rack which holds
the weeds but per-
mits water from the
bypass channel to
re-enter the canal.

A method of tighten-
ing the wires on the
diversion structure
is shown in Figure
176.

Following the adapta-
tion and successful
use of a weed fork,
described subse-

Fig. 175 quently, it became

evident to operators

of the Tule Lake Division of the Klamath Project, California-Oregon,
that a better method of ponding moss in a canal would be needed,
rather than let it pile up at structures.

Floating booms, mesh fencing, trashracks patterned after pumping
plant racks, and many other methods and devices were tried. The

149


The knife, Figure 164, can be made quite quickly and easily from a
part of an old automobile spring, welded to a 1/2-inch pipe coupling,
cut, pointed, and sharpened as required. The pipe coupling can then
be screwed onto the required length of ordinary 1/2-inch water pipe,
to be used as a handle for the knife.

Since material for the knife is readily available from used material,
the main cost is in cutting, welding, and sharpening the blade. Maxi-
mum cost is about $7. 00.

Fy

Fine

nondle--.| Knife blade made from car spring shoped

‘and sharpened, welded to pipe coupling.

|.---FPine coupling

+

--- Variable -—------

WEED KNIFE

TO FACILITATE THE REMOVAL OF WEEDS
FROM WEED SCREENS

Fig. 164

141


ig. 160

138

The groover is con-
structed of heavy metal
and planking. The
plowshares are dis-
carded grader blades

or steel plates with lugs
welded on one side for
bolting into the platform.
The unit weighs about
400 pounds.

The forward lever is
attached to a rolling
coulter which the oper-
ator manipulates to keep
the sled near the center
of the ditch. A movable
arm on the hitch can be
pinned in several posi-
tions to produce a more
direct pull. The verti-
cal staff at rear of the
platform serves only

as a handhold for the
second rider who adds
weight and also helps
balance the sled,


8 feet long from rear to nose and the nose cone is 24 inches in length.
A drawing of the device can be made available by writing the Regional
Director, U. S. Bureau of Reclamation, Boise, Idaho.

Fig. 159

Cutters

Periodic draining and drying of the channels are the most economical
and practical methods of controlling submersed waterweeds. Where

the method can be used, the sun and wind rapidly dry the exposed
weeds and within a few days the tops are dead. Even though water must
be carried in the laterals the year round, the Imperial Irrigation
District operation and maintenance forces practice drying entire
lateral systems for 3 days every 3 weeks, effectively reducing the
weed problem.

Periodically, it is necessary to groove or channel the bottom of the
ditches to connect the low areas and permit rapid and complete drain-
ing so all weeds will dry quickly. This can be done by the unit shown
in operation in Figure 160 being towed by a wheeled tractor. The
device shown in more detail in Figures 161 and 162 was designed and
constructed by personnel of the Imperial Irrigation District, Imperial,
California. Several sizes of the channel groover, sometimes referred
to as the moss plow" have been constructed but each is designed to
slice a groove about 12 inches wide and 8 inches deep.

137


most successful
method, termed a
"moss trap," Fig-
ure 177, consists of
two 30-foot poles or
large timbers placed
parallel to each other
and three 4- by 12-
inch timbers bolted
crosswise, one at
each end and a third
in the middle, thus
two stilling ponds
were formed. The
length of the 4- by
12-inch cross tim-
bers depends on the
width of the canal or
lateral.

Fig. 176 The traps are placed
in the canal or lat-
eral at points readily
accessible to a truck
crane and are held
in place by cables,
As the moss and
weeds are torn laose
by chaining and float
downstream, they
lodge against the
upstream cross
timber of the trap.
Some of the floating
material is forced
under and lodges
against the middle
cross timber. Very
little moss is found
Fig. 177 in the second stilling
pond of the trap.
The blanket of moss lodged against the trap has been 1/4 of a mile
long at times without seriously impeding the flow of water. When
sufficient moss has been ponded, a truck crane removes it witha
fork. The traps are left in place throughout the year.

Trash Booms

A simple floating boom has been installed across the Gila Canal
on the Gila Project, Arizona, at a wasteway immediately upstream

150


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140



£1 68913--, ane

oe + af Projection.

Of Spex 25g hd mach bolt
ve with Ther. nuts, 2
© My) mm thread.

te INSTALLATION

TRASHRACK SEAT
STRUCTURAL STEEL
ONE REQUIRED

- Bor 3h
6" Std pipe-

TRASHRACK SUPPORT
ONE REQUIRED

ft
=

w--End of groting Yo cross members spaced egually-~
Hoo

NOTES
Grating ponels shall be Tipe I welded stee! gelanized
SECTION B-8 Greting conforming with Federel Specifications FR- 6-661 a
rs Spd ith booring ban sizes ard spacing as shown 2” his
} 33 Cross members shell be crewing
& nob less thon sguere Number af ponels paking up the overall width of trashrack
Inch in cross sechonel {to be determined by fe tontracter, buh re pane! to be
oneans less thon Winches wide.

Total estimated weight 2,900 Ibs

REFERENCE DRAWING
AVON SIPHON -'NLET TRANSITION-TRASHMACE
AND CHECK STRUCTURE

566-0-686

UNITED STATES.
DEPARTMENT OF Thad IETERIOR

pp dedi
EPR OSE
scorn ec MENNEWIER BITS OM UAEHINGTON
- MAIN CANAL STA.130]* 27.20 TO STA 19224 6131
T RACK
STE SR NN cc AMON SIPHON
ONE REQUIRED TRASHRACK- SEAT ano SUPPORT

Fig. 185

156



P222-D-29228

Fig. 151

Mechanical Methods for Control of Aquatic Weeds

Numerous devices from hand tools to very elaborate cleaning devices,
have been used for the cleaning of aquatic weeds from canals. The
few illustrations given in this section of the bulletin are typical of
many devices and convey the general idea that disposal is the impor-
tant problem as discussed in a later section,

Chaining and Drags

Removal and disposal of submersed aquatic weeds in large canals is

a problem which has thus far been solved only by mechanical methods.
Chaining, Figure 152, is one of the most used mechanical methods
and consists of the passage of a very heavy linked drag, Figure 153,
over the bottom of the canal.

Usually, at least three passes of the chain drag are required, how-
ever, treatments are repeated as often as necessary to relieve the
aquatic weed problem. Two or three chainings a season would be a
minimum. On other projects the treatments may need to be repeated
every 10 days.

On projects containing many pumps, farm sprinkler systems,

siphons or spiles, project management would chain only as a last resort,
In these instances special diversion structures might be constructed
to keep the water relatively free of weed debris which clog pumps

132


and weed traps. Some of the devices described in the preceding
sections of this bulletin also may play a part in weed disposal.

The diversion of weeds into larger channels and wasteways is often
practical. Where there are pumps in the system, however, the
vegetative debris must generally be removed from the trashracks;
and often this must be done by hand. Unattended or semiunattended
pumping stations must of necessity become attended stations unless:
the weeds can be prevented from occurring; they can be divided into
such small pieces that they are no longer a problem; or the disposal
of the weeds is made semiautomatic.

Self-cleaning trashracks are only semiautomatic. Weeds are
removed from the rack, but they must be destroyed or hauled from
the site.

Disposal of Dry Weeds by Burning

Butane dry weed burning is a disposal process which can be accom-
plished in an unlined channel, as in the case of windblown tumble-
weeds, or on the banks where weeds still in place have not been
prevented or controlled.

Hazards of burning include the escape of the fire to dry range grasses
and damage to flammable structures. The burning of dry weeds is

a once-over job, but strong wind can create a new job overnight, by
loosening tumbleweeds and carrying them into the channels.

Burning of loosened weeds in channels is aided by air movement.
Burning of dry weeds rooted in place may be aided, but is as likely
to be hindered by air movements.

The total amount of heat necessary to ignite dry weeds varies with
the moisture content of the weeds. But it is much less than that
required for green weed burning.

Much of the dry weed burning is intermittent. Oilor L.P. gas
burners described previously under Weed Control are effective,
especially if igniter devices permit the main burners to be turned
off when not needed, and turned on when they are needed. A pilot
light or other form of remote igniter is useful also for the ignition
of burners on long booms.

Long booms and vehicles capable of moving rapidly are essential.
The long booms permit ignition at the bottom of long slopes or
across channels. A vehicle capable of moving at least 10 or 15 miles
per hour is a safety feature. Updrafts, flash fires, and fast changes
in wind direction may cause accidents if the men and equipment can-
not be moved rapidly away.

143



WEED DISPOSAL
The Problem

Weeds which enter a waterway or which become detached after
growing in a waterway must be removed or diverted from the irri-
gation system to prevent their collecting at structures, causing
overflows and the breaking of banks. They also interfere with water
deliveries. The delivery of clean water also is becoming more
important as sprinkler irrigation and the delivery of municipal and
industrial water increases.

A problem with tumbleweeds is illustrated in Figures 165 and 166.
The removal and disposal of dead weeds from this channel is neces-
sary before water can be delivered. They may be rapidly burned
with motorized burners; however, the fine charred debris that
remains may clog pumps of certain types, and may initiate sediment
bars which favor growth of pondweeds. Such channels are usually
flushed thoroughly with water before deliveries are begun.

Fig. 165 Fig. 166

Equipment for disposal of dead or detached weeds may be incorpo-
rated in the same equipment used for mechanical control. Devices,
machines, and structures described in this section include buckets
for heavy motorized cleaning equipment, trashracks, diverters,

142


Fig. 162

Every year small, sluggish sublaterals on the Tieton Division of the
Yakima Project, Washington, become infested with aquatic growths.
The weed growths, together with the silt deposits which accumulate
among them, rapidlyincrease the elevation of the water surface to a
point where corrective action is required. Often the weeds in small
ditches are removed by rakes or by dragging chains behind teams of
horses or small tractors. However, hand-operated devices are use-
ful in very small laterals where the infestation is not heavy or is in
isolated patches,

A hand-type ''moss cleaner"! developed by project personnel to cut the
aquatic plants on the bottom of the ditch is shown in the drawing,
Figure 163, The implement is pushed by the operator wading up the
ditch. Cut weeds float downstream to be removed with a weedhook

at a screen or a structure.

The implement is a diamond-shaped blade of saw steel which is
attached to a fork handle. Both edges of the blade are kept very sharp
so the weeds are cut rather than being pulled. The hardwood handle
is fastened to the blade at an angle of 30°.

Trouble has been experienced at the pumping plants on the Yakima
Project, Washington, from weeds and debris collecting on plant
trashracks and weed screens in such a way as to be very difficult to
remove. A knife for cutting, and thereby loosening the weeds and
debris from the trashracks and screens has greatly reduced the weed
removal problem.

139


Small Trashrack Installations

Fine debris collected on the trashrack on two low-lift centrifugal
pumps is the problem illustrated in Figures 181 and 182 on the
Columbia Basin Project, Washington,

Typical of mate-
rials which can
reduce the output
of pumps is that
shown in Figure
182. Some of this
debris may pass
through a trash-
rack, if the rack
is not cleaned fre-
quently during the
period in which
such debris is a
problem.

Weed racks are
placed at the ends
of siphon structures
to prevent the
entrance of trash,
tumbleweeds, and
animals during the
nonoperating season
on the Cambridge
Canal of the
Frenchman-
Cambridge Unit of
the Missouri River
Basin Project in
Nebraska. The
lightweight racks
similar to the ones
shown in Figure
183, are placed in
the fall after the
irrigation season
and removed the
following spring
before water is
again placed in the
canal system.

The lightweight
racks consist of
pipe, steel rail,

or wooden frames,

to which a wire mesh is attached, The racks have been very effective
and are believed to have reduced O&M costs materially,

Fig. 182

153


> lpcnemennnnrarrvnrwnmensomer =; = Alli

P566-0-29326

Motor and Gearbox Looking Downstream at
Fig. 188A Trashrack and Cleaning Device
Fig. 188B

Flap Gate at Bottom of Canal Flap Gate and Lower
Fig. 188C Portion of Rack
Fig. 188D

159


Ye x4¥2 Die. Washers
4 2 Required 9
V2" 7" Removable pins bk
ree kg i

:

Free to tum thu 360° —

Adjusting Holes Sto © a

ss Pine Approx. 14 tant
= an
= 308

Wire Cable - 12"

be attached to wood by
‘extra heavy staples.

‘Approx. 2° Links-4°
2 Requred

«NOTE
Length of spreaders depentont upon canal section

Fig. 156

135



Fig. 171

The cost in 1950 of installing a weed trap similar to that shown in
Figures 170 and 171 was $175 for a 24-foot-wide canal. Traps for
10-foot-wide laterals were installed for about $50.

146


Check
Weed Trap
|, Bypass Canal

Mon Canat--"\\

Check-- Check
Floating Boom — INLET CHECK DETAILS

4

é/

al,

GENERAL PLAN
Scale: "= 200°
Fence made from #* ren bars
& RB Rails Ft ee
(30 RR Rails © I'ctrs > _~ aa
i: :
| = ==
Landing
: Mat
a Gent Flow
| Check
4 f E
Kk— ---—es' — er ate— 10
PLAN
Fe
__fTop of Bank an ceheck.

Se
?  _

LONGITUDINAL SECTION
WEED TRAP DETAILS

UNITED STATES
DEPARTMENT OF THE INTERIOR
BUREAU OF RECLAMATION
PAYETTE Div.- BOISE PROU.- IDAHO

WEED TRAP
D-LINE CANAL ~ MP 23

DRAWN: R.W.R,

[hows ono - o-540 |

Fig. 173

148



A special platform was
constructed on the trac-
tor hitch as a support
for the boom, The
boom was made from
3-inch pipe to which the
free- swinging butterfly
is fitted and held in the
desired position by two
collar clamps. Being
able to move the but-
terfly back and forth

on the boom permits
the operator to center
the drag in ditches of
different widths and
also allows adjustment
for the distance from
the ditch where the
tractor must operate,

When it is desired to
make a return trip,
the hitch end of the
boom is unpinned and
refastened to the
opposite side of the
platform. The butter-
fly is turned over and
the anchor cable is
hooked into an eye
welded to the track-bar
shield on the opposite
side of the tractor.

The plank spreaders
are necessary to keep
the heavy chain at
proper width to attain
full coverage of the
ditch. Sufficient
length of cable and
chain should be used
so the entire loop lies
flat upon the canal bottom and the pull is as vertical as possible. A
drag that is too short results in an upward pull and the chain passes
over the weeds without breaking or tearing them loose.

Fig. 155

134


BILL OF MATERIAL

Single Phase electric motor HP 4°x4"L 12-0" five
Gear box Weed rack 12'x 5 one
13" shaft 12'-6" one Weed rack 12'x 2' one
12" two 10" Sprocket for 13" shaft four
two 13" bronze bearings two
six link chain 94"
i eck spacing before welding 1 ¥
= Pai
_s8 _L(GRY\ Ground
exe L F ¥ y1\ surface
' I \
H 1 5
' I
' I
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exe Z \
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= Wooden bearings--~

Fig. 186

157



Fig. 153

and farm sprinklers. The problem
is illustrated in Figure 154 on the
Boise Project, Idaho, where weeds
loosened from the bottom of the
canal by chaining have been
deposited on a trashrack provided
for collection of the weeds and
debris, Expensive hand removal
of the debris is necessary where
other facilities are not available.

A study of the relative merits of
pondweed control by chaining and
by treatment by aromatic solvents
on projects in Region 1 was
reported in ''Pondweed Control:
Chaining vs. Aromatic Solvents,"

copies of which may be obtained by addressing the Regional Director,
U. S. Bureau of Reclamation, Boise, Idaho.

A side-arm boom has proved satisfactory for towing demossing
equipment through irrigation ditches where only one ditchbank operat-
ing road has been provided. The boom shown in Figures 155 and 156
was designed by personnel of the Patterson Water Company, Patterson,

California.

133


Butane Burners

Motorized large L.P. gas burners have been in use for some time.
Burning units have been fabricated by the irrigation project operators
or purchased from commercial firms. Recently, also, lightweight,
hand burners have been developed which use the L.P. gas. Both
types of burners are illustrated in Figures 167, 168, and 169.

Fig. 168

An L.P. gas, propane burner with a 33-foot boom in operation on
the Columbia Basin Project is shown in Figures 167 and 168. The

144


Diversion Channel Traps

An effective and economical way of collecting floating material in
the irrigation system may be accomplished by a weed trap similar
to that shown in Figure 172, designed and constructed on the Payette
Division, Boise Project, Boise, Idaho. Regardless of quantity of
plants collected or the resulting damming effect, the water will not
overflow the banks as the weed trap is located in a bypass channel
into which the floating material is directed by a log boom. Weeds
floating in the system are forced upon inclined grating by the current
where they subsequently are burned.

The rack is constructed of railroad rails 30 feet long and placed
with flat side up and held in place by spacers which are far enough
below the canal grade to keep floating weeds from collecting against
the ends of the rails. A crossmember holds the upper end of the
sloping rails about 1 foot above high waterline. A grill supported
by an iron frame levels off from the sloping rails and covers the
entire width of the ditch. The grill itself is made from sheets of
steel airplane runway mats placed over 3/4-inch reinforcing rod
that is welded to the support frame. A railing or fence surrounds
the grill to keep weeds confined until they are dry and can be burned.
Details of the construction of the channel and trap are shown in the
drawing, Figure 173.

Fig. 172

147