Abstract:
Water balance is a method by which we can account for the hydrological cycle of a specific area, with the emphasis on plants and soil moisture. One of the main purposes of a water balance study is to evaluate the net available water resources, both on the surface and in the subsurface. Understanding the behavior of a catchment from a hydrological point of view is necessary when planning and activities needed to be done in the watershed.
A-two parameter monthly water balance model for two basins was calibrated and verified using 30 years monthly rainfall, observedflow and pan evaporation data. Kalu Ganga at Ellagawa and Mahaweli Ganga at Morape were selected to estimate the streamflow. The model was calibrated and verified and a good performance was shown for both catchments. The C coefficient for Kalu Ganga at Ellagawa and Mahaweli Ganga at Morape were found as 1 and 1.1 respectively while the SC parameter was found as 800 and 1200 respectively.
The MRAE value for calibration period for Kalu Ganga at Ellagawa and Mahaweli Ganga at Morape showed a very good fitting with value of 0.145 and 0.152 respectively. The same for verification period was also very good with value of 0.153 and 0.157 respectively. During the calibration and verification periods value of the Nash–Sutcliffe efficiency for Kalu Ganga at Ellagawa was found as a 93.6% and 92.4% respectively. 93.6% and 94.1% were the Nash–Sutcliffe values for Mahaweli Ganga at Morape respectively. The two parameter monthly water balance model produced a better fitting of MRAE in annual and seasonal values when compared with monthly time series.
The two-parameter monthly water balance model with the simple structure and two parameters proved as a very efficient model when simulating the monthly, seasonal and annual runoff. Due to its simplicity and high efficiency in performance, this two-parameter monthly water balance model can be easily and efficiently used for the water resources planning and management.
