| Abstract | In Thailand, a typical irrigation system composes of canals, channels, drainage and
civil works. Water is stored in reservoirs such as dams, ponds for supply to irrigated
areas mainly by gravity, and in some cases water is diverted from natural rivers to
irrigation canals. Therefore, aquatic weeds from reservoirs and rivers can move with
water into irrigation networks and continue growing in both earthen and concrete
lined canals where deposited sediment is available for their root substrate. Based on
reports and researches, as many as 116 species of weed listed as major weeds in
Thailand, but a few were considered to be serious, such as water hyacinth (Eichhornia
crassipes), hydrilla (Hydrilla verticillata), pondweed (Potamogeton malaianus),
waterfern (Salvinia molesta), water primrose (Ludwigia adscendens), giant sensitive
plant (Mimosa pigra), parrot feather (Myriophyllum spicatum), and water lettuce
(Pistia stratiotes). Among these seriously problematic species, the dominating weeds
in irrigation canals are hydrilla and pondweed. These submerged weeds result
seriously impeded flow of water by 40-70% of the designed discharge, blocking
regulators and pump intakes.
Therefore, removal of the weeds from the irrigation networks is necessary for
improving irrigation efficiency. A few imported and expensive aquatic weed
harvesters have been used to control aquatic weed in irrigation canals of Thailand, but
owing to their large size and heavy weight, their effectiveness are limited. They may
not be effectively used in areas of dense weed infestation and in the cases of earthen
canal with low bearing capacity of soil. The cost for transportation of harvesters to the
infected area is unacceptably high and inconvenient – especially in case of urgent
cleaning operation requirement. Therefore, the development of an appropriate aquatic
weed harvester, which is conveniently mobile to remote areas where heavy harvesters
cannot be transported, and can be operated in both concrete lined and earthen canals,
is greatly required.
This research aimed at designing, testing and developing an aquatic weed harvester
with aforementioned desired characteristics. The process of development consisted of
two parts. In the first part, characteristics of the hydrilla and pondweed were
investigated through laboratory and field tests of their physico-mechanical properties;
and in the second part of the research, characteristic values of the aquatic weeds were
used in the design and later on in development of the desired harvester – subsequently
followed by its performance evaluation.
Measurements of weed physico-mechanical properties, stem diameter, weed density
and uprooting force, were performed in densely infestation areas. Results revealed
that 82.82% of hydrilla stems diameter was between 1.0 to 2.0 mm, and its density
and wet weight were between 50 to 270 stem/m2 and 0.31 to 3.37 kg/m2 respectively.
About 91.27% of pondweed stems diameter was between 1.0 to 2.5 mm, and its
density and wet weight were from 25 to 240 stem/m2 and 1.45 to 7.98 kg/m2
respectively. Uprooting force requirement for hydrilla and pondweed was recorded as
the maximum force per stem of 7.85 and 9.81 N for hydrilla and pondweed
respectively. The maximum tensile force per stem ranged between 1.72 to 2.82 N and
3.55 to 4.59 N for hydrilla and pondweed respectively.
iv
Based on the physico-mechanical properties of the weeds, design values of crucial
mechanical parts of the prototype harvester were determined. The designed prototype
consisted of two main components: a harvesting unit and a carrying unit. Furthermore,
the harvesting unit comprises two components, a chopper and a suction pipe. It was
tested in the laboratory to obtain important correlations between: the length of cutweed
and spike tooth drum rotating speed of chopper; propeller rotating speed and
water discharge through the suction pipe; and the water cut-weed ratio and shaft
rotating speed in suction pipe. The correlations form laboratory tests and weed
properties were used in design of the harvester. An aquatic weed harvester prototype
consisting of a harvesting unit and a carrying unit was developed. The harvesting unit
included a chopper to pull and cut the weeds and a suction pipe to carry chopped
weeds to a porous basket fixed on the carrying unit of appropriate capacity to carry
harvesting unit, harvested weeds and operators. The parameters namely physicomechanical
properties of the weed, weed density (number of stems/m2), weight
density (kg/m2), force (N) to uproot weeds from soil and tensile force (N) to cut weed
stem into small pieces were considered to design the harvesting unit.
The machine was then fabricated by the author in a local workshop. The prototype
harvester comprises two main components: a harvesting unit, consisting of a chopper,
a suction pipe, and one engine as power source for driving the harvesting unit and a
carrying unit, consisting of a couple of shuttle fiberglass pontoons, aluminum
platform, canvas roof, guard rail, aluminum perforated basket, and one engine as
power source for driving the carrying unit. Overall dimension of the prototype
harvester is 1,700 mm x 5,400 mm x 3,100 mm (width x length x height). The
harvester consisted of a 13 hp gasoline engine (Honda, Model GX390) to operate the
harvesting unit, rotating drum of chopper and impeller of the suction pipe of 15 cm
diameter and 2.0 m long. The harvesting unit was installed on a carrying unit of 1.7 m
wide and 5.4 m long carrying unit composed of two 4 m long fiber glass pontoons that
can carry 2,000 kg of total toad. It was driven by another 9 hp gasoline engine
(Honda, Model GX270) through a long rudder propeller, which can be operated
separately from the harvesting unit. The total weight of the harvester was about 560
kg. The maximum harvesting depth was 1.0 m from water surface. The minimum
working water depth and canal width that the harvester can be operated are 0.5 and
2.0 m respectively. The harvesting capacity for hydrilla at the highly infestation for
the weed density of 25 ton /ha was 1.9 ton/h at 2 km/h operational travelling speed.
The maximum fuel consumption in operation of harvester is 3.0 l/h. Two operators
are required for operating harvester, one for steering the harvester another for
operating the harvesting unit |