[AHW32-14] Assessment of hydrological processes and sediment yield in Dakbla catchment, Kon Tum province, Vietnam.
キーワード：Water discharge, Soil loss, Agricultural fields, Central Highland of Vietnam
The Dakbla catchment, a sub-basin of Se San river basin, is located in the Central Highland of Vietnam with an area of about 3,507 km2, the length of the main river is 152 km. As it belongs to the tropical monsoon climate, there are two distinct seasons including rainy season (May - October) and dry season (November - April). The average annual temperature is about 20 - 25oC and the total annual rainfall is 1,500 - 3,000mm. The meteorological and hydrological monitoring system has not been invested and developed. Moreover, the economy in the study area depends heavily on cultivation activities with the main crops such as rubber and coffee grown on basalt soil. During rainy season, intensive rainfall has damaged farmlands and accelerated soil erosion from the areas. Thus, soil fertility in farmlands and crop productivity have been reducing. Therefore, simulating the flow and sediment yield are extremely important as the first step to understand an impact of land degradation in the catchment against local economy, based on the historical time series.
At present, there are many critical issues for water resource management ranging from hydrological variability, environmental degradation, erosion, and conflicts over the use of water for different purposes. So far, many studies have assessed water discharge in Dakbla catchment but still lack of data on sediment and water quality. In this study, SWAT model, a physically based semi-distributed hydrological model, was selected to assess hydrology and water quality in an agricultural catchment. The results showed that model was calibrated and validated for the period 2000 - 2005 and 2006 - 2011, respectively, using the observed water discharge data at Kon Tum station. Statistical evaluations including R2 (coefficient of determination) and NSI (Nash–Sutcliffe index) indicated good performance of the model in simulating water discharge on monthly time step during the calibration and validation period. The calibration result of water discharge at Kon Tum station from 2000 to 2005 was good with R2 = 0.78 and NSI = 0.77. Similar to the calibration period, water discharge was simulated well with R2 = 0.82 and NSI = 0.80 during the validation period (2006 - 2011). Focusing on sediment yield, the results were R2 = 0.70, NSI =0.70 in calibration period, and R2 = 0.58, NSI = 0.50 in validation period, respectively. As next step, it is very important to assess local farming activities and to analyze its influence for sediment discharges from agricultural fields.
At present, there are many critical issues for water resource management ranging from hydrological variability, environmental degradation, erosion, and conflicts over the use of water for different purposes. So far, many studies have assessed water discharge in Dakbla catchment but still lack of data on sediment and water quality. In this study, SWAT model, a physically based semi-distributed hydrological model, was selected to assess hydrology and water quality in an agricultural catchment. The results showed that model was calibrated and validated for the period 2000 - 2005 and 2006 - 2011, respectively, using the observed water discharge data at Kon Tum station. Statistical evaluations including R2 (coefficient of determination) and NSI (Nash–Sutcliffe index) indicated good performance of the model in simulating water discharge on monthly time step during the calibration and validation period. The calibration result of water discharge at Kon Tum station from 2000 to 2005 was good with R2 = 0.78 and NSI = 0.77. Similar to the calibration period, water discharge was simulated well with R2 = 0.82 and NSI = 0.80 during the validation period (2006 - 2011). Focusing on sediment yield, the results were R2 = 0.70, NSI =0.70 in calibration period, and R2 = 0.58, NSI = 0.50 in validation period, respectively. As next step, it is very important to assess local farming activities and to analyze its influence for sediment discharges from agricultural fields.