Hydraulic changes of three reservoirs (Minneriya, Udawalawe and Victoria) in Sri Lanka
E I L. SILVA and F. SCHIEMER
Hydrological characteristics of three Sri Lanka FISHSTRAT reservoirs namely Minneriya, Udawalawe and Victoria were examined. Victoria reservoir, which is located about 438 m amsl, has the steepest gradient and the largest volume. The gradient of Minneriya and Udawalawe reservoirs which are located in the lowland is more or less similar but the capacity of Minneriya is 50 % that of Udawalawe. The seasonal water level fluctuation in the three reservoirs is influenced by seasonal rainfall and release pattern but shows moderate changes during different years. When compared to the annual draw-down from 1994 to 1999 it was lowest in Minneriya (4.22 m) in 1996 and highest (7.05 m) in 1994 with a six year average of 5.91 m and the draw-down in 1999 was 6.62 m. The Udawalawe reservoir had the lowest annual draw-down of 7.71 m in 1995 compared to its highest (11.9 m) in 1994. The six years average in Udawalawe was 8.20 m and the water level dropped by 7.05 m in 1999. In Victoria, which had an average annual draw-down of 35.3 m for a period of six years had the lowest draw-down (13.3 m) in 1995 and the highest was 47.4 m in 1996 and the draw-down in 1999 was 28.8 m. The littoral exposure resulting from draw-down was highest in Minneriya (82 %) and it was 60.3 % and 52.6 % in Victoria and Udawalawe respectively in 1999. The flushing rate in 1999 was 5.5 times per year in Udawalwe and it was 4 9 and 3.8 time per year in Mimieriya and Victoria reservoirs respectively. The magnitude and seasonal pattern of dam site rainfall was different among the three reservoirs in 1999 and it has no relationship to seasonal fluctuation of water level.