The hydrological models are typically classified in stochastic, lumped conceptual and detailed physically-based models. Among these models, only physically-based models consider spatial distribution of driving factors and describe the physical processes by mathematic equations. In this study, the semi-distributed model QSWAT model is selected to simulate the flow to Dak Wi reservoir in Kon Tum province.
Tuyển tập Hội nghị Khoa học thường niên năm 2018 ISBN: 978-604-82-2548-3 A SIMULATION OF INFLOW TO DAK WI RESERVOIR BY THE MEAN OF SWAT MODEL Nguyen Thanh Thuy Faculty of Hydrology and Water resources, Thuyloi University Email: thanhthuy_rt@tlu.edu.vn INTRODUCTION May to October Each season lasts for The flow regime has been changed under months, however, 80-90% of yearly precipitation is in the rainy season the climate and land use change conditions There was no hydrological station at the To support the river basin management, a outlet of Dak Wi reservoir Therefore, the mathematical model which can simulate the influence of these two factors on the flow catchment with the outlet at Trung Nghia hydrological station was selected for should be used to simulate different scenarios The goal of this study is applying a calibration and validation Dak Wi was defined as a sub-basin of Trung Nghia basin such model to simulate the flow under current condition The calibrated and (Figure 1.) validated model will be the primary condition to conduct further studies such as water quality modelling and assessment of climate change on water quantity and water quality The hydrological models are typically classified in stochastic, lumped conceptual and detailed physically-based models Among these models, only physically-based models consider spatial distribution of driving factors and describe the physical processes by mathematic equations In this study, the semi-distributed model QSWAT model is selected to simulate the flow to Dak Figure Trung Luong basin Wi reservoir in Kon Tum province The DEM with resolution of 90 m was used STUDY AREA AND DATA (http://opentopo.sdsc.edu/raster?opentopoID Dak Wi reservoir is located in Dak Wi =OTSRTM.042013.4326.1) The soil type river which is a branch of Krong Po Co river and land use maps were subtracted from The catchment area with the outlet at the dam Global Land Use map of Dak Wi reservoir is 83 km The observed (https://landcover.usgs.gov/global_climatolo data at Kon Tum meteorological station gy.php) and Digital World Soil map indicates that the annual precipitation is (http://www.fao.org/geonetwork/s rv/en/metada around 2600-3000 mm and divided into dry ta.show?id=14116), respectively There are and rainy seasons Dry season is from rain gauges including Dak Glei, Dak To, Sa November to April and rainy season is from Thay, Kon Plong and Kon Tum are located 603 Tuyển tập Hội nghị Khoa học thường niên năm 2018 ISBN: 978-604-82-2548-3 inside and close to Trung Nghia catchment RESULTS AND DISCUSSIONS The observed daily discharge is available Calibration during the period 1991-1997 at Trung Nghia Figure a shows that the water balance was station Therefore, the meteorological and simulated very well with the small hydrological data since 1988 to 1997 was discrepancies between the simulated and used for model calibration and validation observed accumulated volume for the period 1991-1995 The differences increase due to METHODOLOGY the overestimation of flow in the flood season The SWAT model is a semi-distributed of year 1992 The gaps in accumulated model developed by the United States volume between the simulation and Department of Agriculture (USDA) In this measurement are eliminated in the end the study, we used the QSWAT interface for flood season of year 1994 due to the QGIS The SWAT model divides the overestimation of flow in this flood season watershed into sub-basins connected by a In total, the accumulated volume in the stream network, and further delineates each simulation is solely 7% higher than the sub-basin into hydrologic response units counterpart in the measurement Overall, the (HRUs), which consist of unique flow in the dry season is simulated better combinations of land cover, soil type and/or than the flow in the wet season with higher slope It is assumed that there is no values of NASH and R coefficients (Table 1) interaction between HRUs (Neitsch et al 2011) SWAT simulates each HRU separately and calculates daily water balances (Eq 1) t SWt SWo ( Rday Wsurf Ea wse ep Qgw ) (1) i1 Where SWt is the final soil water content (mm H2 0), SWo is the initial soil water content (mm H2 0), t is the time (days), R day is the amount of precipitation on day i (mm H2 0), Qsu rf is the amount of surface runoff on day i (mm H2 0), E a is the amount of evapotranspiration on day i (mm H2 0), wseep is the amount of evapotranspiration on day i (mm H2 0), wseep is amount of percolation and by pass flow exiting the soil profile bottom on day i (mm H2 0) and Qgw is the amount of return flow on day i (mm H2 O) The SWAT model has been widely calibrated and validated through the comparison of observed and simulated streamflow data Most of the studies indicates that CN2 , AWC, ESCO and SURLAG are the most sensitive parameters to surface while GW_ALPHA, GW_DELAP, GW_REVAP and REVAPMN are the most sensitive parameters to baseflow (Arnold et al 2012) Figure Accumulated volume (top) and flow (bottom) in calibration and measurement at Trung Nghia station f or the period 1991-1995 Figure b presents the flow time series in simulation and measurement The low flow and median flow are simulated very well However, there are large differences between high flow in simulation and high flow in 604 Tuyển tập Hội nghị Khoa học thường niên năm 2018 ISBN: 978-604-82-2548-3 measurement The highest discharge is 2300 With the calibrated values of parameters, m3 /s in the historical data while it is 4050 the inflow to Dak Wi reservoir is defined m3 /s in the simulation with mean values of 3.43 m /s and standard Validation deviation of 6.39 m3 /s (Figure ) During the first months of year 1996, the Table Values of NASH and correlation accumulated volume in the simulation is very (R) coefficients calculated for monthly close to the counterpart in the measurement flow in dry and wet seasons in calibration However, the historical data witnesses a and validation sharp increase in the flow since beginning of Dry season Wet season October 2016 to end of December 2016 The NASH (-) R (-) NASH (-) R (-) accumulative volume calculated from the 0.93 0.97 0.79 0.94 observed time series is 17% higher than the Calibrat ion one from simulation results on on 1/1/1997 Validation 0.72 0.88 0.25 0.56 The overestimation of flow in 1997 reduces the gaps in accumulated volume between simulation and observation The difference is solely 1.3% in the end of 1997 The values of NASH and R coefficients are high for flow in the dry season and very low for flow in the wet season Figure Simulated flow time series at the outlet of Dak Wi sub-basin CONCLUSIONS The model for Trung Nghia catchment in SWAT has been calibrated and validated to measured data The set values of parameters cannot simulate the high flow poorly for several years However, they perform very well for dry season and total water volume They can be used for the water balance simulation To improve the accuracy of Figure Accumulated volume (top) and f low simulation results, more investigation should (bottom) in validation and measurement at be conducted for parameters and input data Trung Nghia station for the period 1996-1997 REFERENCES The flow in dry seasons are simulated very [1] Neits ch S.L., Arnold J.G., Kiniry J.R well Nevertheless, the large discrepancies (2011) Soil & Water Assessment Tool exist between the flow in flood seasons Theoretical Documentation Version 2009 There are some flood events in the beginning Texas, US of rainny seasons while there is no flood [2] Arnold, Jeffrey G et al (2012) SWAT: events observed in the historical data Model use, calibration, and validation Addtionally, the highest flow in the observed Biological Systems Engineering: Papers and data is 1610 m /s while it archives the value Publications 406 of 3870 m /s in the simulation 605 ... series at the outlet of Dak Wi sub-basin CONCLUSIONS The model for Trung Nghia catchment in SWAT has been calibrated and validated to measured data The set values of parameters cannot simulate the. .. With the calibrated values of parameters, m3 /s in the historical data while it is 4050 the inflow to Dak Wi reservoir is defined m3 /s in the simulation with mean values of 3.43 m /s and standard... been widely calibrated and validated through the comparison of observed and simulated streamflow data Most of the studies indicates that CN2 , AWC, ESCO and SURLAG are the most sensitive parameters