سال انتشار: ۱۳۸۴
محل انتشار: سمپوزیوم برآورد عدم قطعیت در مهندسی سد
تعداد صفحات: ۹
L. W. SENEVIRATNE – Deputy Director of Irrigation, Irrigation Department, Colombo, Sri Lanka
Tropical countries are periodically subjected to wind generated by annual Earth orbital motion.Monsoon is the wind carrying precipitation in South Asia and Southeast Asia. Recently due to global warming in climate, major changes took place in rainfall patterns. Earth orbital motion with fixed inclination of NS axis creates monsoon in Dec-Jan from NE and May-Jun from SW to precipitate water to Sri Lanka. In addition inter-monsoons caused by crossing the Sun over Sri Lanka come in September and April. Around the same time frontal type cyclones develop with heavy floods. Traditionally combined effect is used to compute the uncertainty of floods. Global warming is a phenomenon in all tropical countries. South Asia has increased mean temperature by 10C during the last 60years. Astronomical features observed during the same time revealed many cyclic events leading to floods and droughts. The common plane episode of Moon and Earth leads to a prolonged drought in tropics as happened in 1974, 1983, 1992 and 2001. The short-term effects of heavy planets like Jupiter and Saturn are causing floods in half year when the earth is in between them and Sun. Full moon days are rainy in Sri Lanka. These astronomical aspects are excluded in calculating the design floods for spillways. The shift in precipitation made Hambanthota dry and Puttalam, Kandy wet. Embankment designs carry greater impact from this shift. 200year storm selected for spillway design is revised. Greater impact has shown over earth slips in wet zone. Dry zone old major tanks need rehabilitation to suit the new conditions. Each basin needs reassessment of certainty in parameters using fresh data. Coastal hydraulics needs designs to face Tsunami in addition to Sea erosion. Discovery in droughts and floods is common to tropics. Brazil had the same drought in 2001 as predicted by the author in 1993. Astronomical features appeared in cyclic form during the last 30years when the global warming increased in tropical countries. Variation in rainfall patterns is a classic example of sources to identify exceptions. Flood hydrology is disturbed when the normal rainfall is concentrated to less duration and increased droughts cause insufficient water in the reservoirs.