Statistical analysis to find the assosiations of daily flows at Ellagawa with rainfall and temperature

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.