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"Based on a case study of water management in the Kirindi Oya Irrigation and Settlement Project (KOISP) in southern Sri Lanka, this report describes the constraints in seasonal scheduling of water allocations from relatively small reservoirs that were not designed to carry storage from one season to the next. Predicting reservoir inflow is complicated because of annual variations in the beginning and end of the rainy season, as well as the amount of seasonal rainfall.
"In the case of KOISP, irrigation scheduling is confounded by changes in the catchment that have resulted in periodic water scarcity. These changes have occurred since 1986 when the Lunugamwehera reservoir started operations and large-scale migration of settlers in the upstream catchment increased the local water demand. As a result, estimated average annual inflow into the reservoir started to decline. The problems are most acute during periods of low rainfall, for instance, during the 1992 yala (dry season from April to September) and the 1999 yala.
"Crops failed completely during the 1992 yala, except in one part of KOISP served by a separate reservoir (Wirawila tank). This resulted from the fact that farmers had planted paddy in the entire Ellegala Irrigation System (EIS) in spite of warnings from the Irrigation Department (ID) that water levels in the reservoir were low. Reservoir inflow during the season was also lower than expected.
"Stakeholder participation and farmers acceptance of advice from the ID had improved much in the 1999 yala. This seasons crop production was successful, although rainfall was much below average. This can be attributed to rotational operation of the system, but especially to greater cooperation from Distributary Channel Organization (DCO) leaders, ID staff and representatives of the farmer organizations (FOs). On the basis of the experience gained in the 1999 yala, members of the ID staff now argue that the yala inflow in years with water scarcity should not be taken into account when planning the yala cropping, but kept instead in reserve in the reservoir for a timely start of the following maha (wet season from October to March) cropping.
"The farmers have learned to be more disciplined in their water use, and to value the reuse of drainage water, which was earlier not considered suitable for irrigation. It was found that farmers in the EIS, who have clayey or clay-loam soils may actually have higher yields in waterscarce years than in normal years. Further investigation is needed to determine the exact reason. Interestingly, most farmers who had high yields in the 1998 yala had even higher yields in the 1999 yala, although the average yields of 1999 were much lower than those of the previous year. Most farmers growing high-yielding varieties are located in the EIS. Farmers located in the Right Bank (RB) were especially affected by water scarcity at all stages of crop growth. Apparently, inequity in water distribution, due both to location within the system and to head-tail differences along canals, is exacerbated during dry years." |
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