AQUATIC WEED REMOVING MACHINE FOR THE SRI LANKAN IRRIGATION SYSTEMS
Dr. Sumith Baduge, PHd.
PUBLISHED ON August 12, 2021
Aquatic weeds are plants which grow and complete their life cycle in water and cause harm to
aquatic environment directly and to related eco-environment relatively. Water is one of most
important natural resource and all lives on the earth depend on it. Therefore, appropriate
management of water from source to its utilization is necessary to sustain the normal
functions of life. The presence of excessive aquatic vegetation influences the management of
water in irrigation systems including natural waterways, manmade cannels and reservoirs.
In the Southern province, for the agricultural and house hold purposes more than 843
reservoirs and tanks are utilized throughout a year. Most of the water tanks are connected
with irrigation systems to supply water to faddy fields and cultivated lands. Now a day it
is identified that growing of aquatic vegetations/weeds causes numerous effects not only the
water tanks but also to irrigation channels connected to the water tanks.
Harmful Effects of Aquatic Weeds
Reduces water storage capacity in reservoirs, tanks, pondsbr
Impedes flow and amount of water in canals & drainage systems
Reduces fish production
Interfere with navigation and aesthetic value
Promote habitat for mosquitoes
Aquatic weeds have been found to severely reduce the flow capacity of irrigation canals
reducing the availability of water to the farmers field. Aquatic weeds may also damage pumps
turbines in super thermal power stations and hydroelectric power stations influencing
production and increasing the cost of maintenance of power stations.
In flowing water system, aquatic weeds impede the flow of water in irrigation canals and
drainage channels thereby increasing evaporation damage structures in canals and dams, clog
gates, siphons, valves, bridge piers, pump etc. Impediment in flow of water may result in
localized floods in neighboring areas. The velocity of flowing water is reduced by about 30
- 40 percent due to the presence of aquatic weeds.
Dense weed growth slows the flow of water in rivers, canals and drainage ditches allowing
silt to settle out and be deposited on the bed of the water body. This increase in silt
deposition raises the bed level and finally affects the life of lakes, dams, tanks etc. and
requires expenditure to be increased for frequent desilting through dredging.
Aquatic weeds (emergent, floating and submerged) interfere with the static and flow
water system. They cause tremendous loss of water from water bodies like lakes and
dams through evapo-transpiration.
Aquatic weeds often reduce the effectiveness of water bodies for fish production.
Aquatic weeds can assimilate large quantities of nutrients from the water reducing their
availability for planktonic algae. They may also cause reduction in oxygen levels and
present gaseous exchange with water resulting in adverse fish production. Although
excessive weed growth may provide protective cover in water for small fish growth it
may also interfere with fish harvesting.
Dense growth of aquatic weeds may provide ideal habitat for the development of
mosquitoes causing malaria, encephality filarasis. These weeds may also serve as
vectors for disease causing organisms and can greatly reduce the aesthetic value of
water bodies from a recreational point of view.
Aquatic weeds in Sri Lanka
There are many number of weed species which emerge according to to various habitat.
There includes shallow and deep reservoirs, cannela with earthen and lined
embankments and drainage systems with lined and unlined bunds. Some dominiant
weed of the aquatic environment of Sri Lanka are Eichhornia Crassipes, Salvinia
molesta, Salvinia auriculata, S. accicenlata, Potamogeton stratiotes and Panicum repens.