Abstract:
Kalu ganga is one of the main rivers use for water supply in Sri Lanka. There are many
agricultural areas and plantations around Kalu ganga bellow the Ellagawa catchment. Studying the
relationship of flows of Kalu ganga at Ellagawa catchment with the rainfall and the temperature is very
important. Objective of this study was to find the associations of rainfall and temperature with the
flows of Kalu ganga at Ellagawa. The data was collected on over the period of January 2001 to
December 2006. Daily flow in m3/s at the Ellagawa gauging station was obtained from the Hydrology
Division of Irrigation Department. Daily rainfall in mm in the selected eleven rainfall stations within the
catchment area (Galathura, Wellandura, Eheliyagoda, Keragala, Balangoda, Alupola, Hapugastenna,
Rathnapura, Landsdown, Halwathura and Deepedena) and Maximum daily temperature in centigrade
at the Rathnapura Meteorology station was obtained from the Department of Meteorology.
Regression analysis was used in the analysis. Natural logarithm of flow (Ln-Flow) was used in
model building instead of flow. Average Ln-Flow per day for each month in every year at Ellagawa
was the response variable(Y). Thiessen Polygon Technique was used to find the average rainfall
(Av-Rf) of the Ellagawa catchment. Average Av-Rf per day of the Ellagawa catchment(X1) and
average maximum daily temperature at Rathnapura per day(X2) for relevant month in relevant year
were the predictors. The fitted model is Y = 6.49 + 0.0805 X1 - 0.115 X2 (R-Sq = 85.4%, PRESS =
2.42829, tolerance > 0.9). According to the fitted model the Response Y is collectively associated with
the predictors X1(p=0.00) and X2 (p=0.00). The ratio (Daily Flow / Fitted Daily Flow) for the period of
January 2001 to December 2006 was estimated and results indicate that the model is fairly good for
predict the daily data.
