Results on vector breeding

The irrigated areas, which are densely populated, showed low malaria incidence. In contract, the sparsely populated areas outside the irrigated areas, where slash and burn cultivation is practiced, have very high malaria incidence.

The population living in the slash and burn cultivation areas is poorer than the population in irrigated areas and low socio-economic status is an independent risk factor for malaria. Most people do not consider malaria as a problem, though people living in the irrigated area do find mosquitoes a nuisance and use all kinds of measures to protect themselves, such as burning mosquito coils and sleeping under a bed net.

Abundance of immature Anopheles was greater in the irrigated area than in a comparable area nearby, north of Thanamalvila town before the onset of the rainy season. When the rains started in mid-October, a sharp increase in immature Anopheles occurred in the area with slash and burn cultivation and abundance remained greater than in the irrigated area for the remainder of the study period.

Total abundance of adult Anopheles was higher in the high malaria area throughout the study period than in the irrigated area. In the areas under construction, several hydraulic structures create a health risk by providing excellent breeding sites for malaria mosquitoes. A notable risk came from drop structures that were constructed but were not yet operational and which accumulated large numbers of the malaria vector after rainfall.


Results on water for domestic uses

Before lining, groundwater levels fluctuated mildly with water flows in the irrigation canals and more extremely between irrigation seasons with rainfall. After lining, the groundwater was more stable, but at a lower level than before the intervention and some shallow wells dried up.

The water quality analyses had shown that protected shallow wells provided the best drinking water. Water from deeper boreholes often had high fluoride, iron and salt content. Surface water had high fecal contamination.

The extensive hydro-geological studies confirmed the influence of the irrigation water on the groundwater. The highest concentrations of fluoride, both in shallow (dug wells) as in deeper groundwater (tubewells) are found in the eastern part of Uda Walawe, with slash and burn cultivation. The major source of fluoride in the region is biotite, from hornblende bearing rocks. In the irrigated areas, recharge with of lower fluoride-containing surface water plays the major role in diluting the high concentration of fluoride in groundwater. Mixing of groundwater with surface water increases the dissolved constituents, but does not always minimize the risk of high fluoride concentrations, which was confirmed by the dental survey.

The shallow groundwater that turns out to be the safest water for human consumption was now threatened by the lining intervention. From simulation exercises in the newly planned area, it appeared that if the irrigation system would be extended according to the design, the important coastal town of Hambantota would be flooded for more than half of the time. The project has recommended to the irrigation agency the construction of a drain to discharge directly to the sea, bypassing the lagoon.


Results on pesticides

The research results show that the most commonly used pesticides in Sri Lanka, mainly organophosphates and carbamates, may cause poisoning by inhibition of acetylcholinesterase.

Pesticide use was extremely high on vegetables, much lower on paddy, and the lowest for bananas.

Both acute and long-term exposure symptoms were more prevalent in farmers. As more farmers change from rice to banana or vegetables, the need for pesticides is likely to increase. However, the irrigation agency, in collaboration with the agricultural extension service, is very active to promote integrated pest management by organizing training for farmers. This training seemed to result in less insecticide use, and less cholinesterase inhibition.

The main conclusion of the study was that overall reduction in pesticide use seems the best option to protect farmers from the adverse effects of pesticides.