(Luận văn) application of swat model to assess the impact of land use changes on stream discharge in nghing tuong watershed, thai nguyen province

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY DINH NGOC HUAN TOPIC TITLE: “APPLICATION OF SWAT MODEL TO ASSESS THE IMPACT OF LAND-USE CHANGES ON STREAM DISCHARGE IN NGHINH TUONG WATERSHED, THAI NGUYEN PROVINCE” BACHELOR THESIS an Lu va n Study Mode: Full-time Major: Bachelor of Environmental Science and Management Faculty: International Training and Development Center Batch: 2010 - 2015 ac th si nl w d oa an lu lm ul nf va Thai Nguyen, January 2015 oi at nh z z DOCUMENTATION PAGE WITH ABSTRACT Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor of Environmental Science and Management Student name Dinh Ngoc Huan Student ID DTN1054110040 Thesis Tittle Application of SWAT model to assess the impact of land-use changes on stream discharge in Nghinh Tuong watershed, Thai Nguyen Province Suppervisor (s) Phan Dinh Binh, Ph.D Abstract: The purpose of this research is to implement “Soil and Water Assessment Tool (SWAT)” model and GIS to evaluation, assessment impact of land-use changes on stream discharge in Nghinh Tuong watershed (riverhead Cau river watershed) an Lu in Northern Viet Nam The watershed were cover by 56% forestry land, 30% n va agricultural land, and remain for others Stream discharge observed data 2002 - ac th 2012 were used for calibration (2002 - 2007) and validation (2008 - 2012) The si result shown that two coefficients (NSE and PBIAS) to evaluate model nl w performance were 0.76 and 6.54% for calibration period and 0.87 and 4.74%, oa d respectively Stream discharge strongly depends not only on quantity of lu an precipitation but also on land use change Through the scenario 1, agricultural va lm ul nf land (corn, orchard and tea) increases 9782.67 (2.45%), meanwhile forest (forest-mixed) decreases 1091.77 (2.75%) as compared to baseline scenario oi at nh ii z z Additionally, precipitation increases 3.74% in mean wet season, but decreases 0.5% in mean dry season with respect to baseline period SWAT model was able to simulate stream discharge and sediment yield for Nghinh Tuong watershed successfully not only for Baseline scenario but also for Scenario In brief, SWAT proves its ability in simulation stream discharge and sediment yield in watershed level It is a useful tool to assist water quantity and quality management process in Nghinh Tuong watershed Keywords: Key words: stream discharge, watershed, GIS, SWAT model, scenario Number of pages: 50 Date of Submision : January 15, 2015 an Lu n va ac th si nl w d oa an lu oi lm ul nf va at nh iii z z ACKNOWLEDGEMENT First and foremost, I wish to express my sincere thanks to the boards of Thai Nguyen University of Agriculture and Forestry, Dean of Faculty Natural Resources Management, Department of Remote sensing and Surveying of Thai Nguyen University of Agriculture and Forestry for providing me all the necessary facilities and all the teachers who built me the scientific knowledge to complete this research In particular, I would like to thank my principal research adviser Dr Phan Dinh Binh who guided me wholeheartedly when I implement this research project I place on record, my sincere gratitude to all staffs, government and people in Nghinh Tuong commune Vo Nhai district and Van Lang commune Dong Hy district, Thai Nguyen province for their expert, valuable guidance and generous support to our project Finally yet importantly, I take this opportunity to express our deepest Lu an appreciation to our families, relatives, friends and fellow students in class of va n K42-Advanced Education Program who encouraged and supported me th ac unceasingly and all who, directly or indirectly, have lent their helping hand in si d oa Thank you very much! nl w this venture an lu Thai Nguyen, January 15, 2015 lm ul nf va Student oi Dinh Ngoc Huan at nh iv z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 TABLE OF CONTENTS ACKNOWLEDGEMENT iv TABLE OF CONTENTS v LIST OF TABLES viii LIST OF FIGURES ix LIST OF ABBREVIATIONS xi Part 1: INTRODUCTION 1.1 Research rationale 1.2 Research’s objectives 1.3 Research questions and hypotheses 1.4 Limitations 1.5 Definitions Part 2: LITERATURE REVIEW 2.1 Research situation Lu an 2.2 Soil and Water Assessment Tool (SWAT) Model va n 2.2.1 Concept of SWAT th ac 2.3 SWAT Theory si nl w 2.3.1 SWAT hydrologic component d oa 2.3.2 The land phase of the hydrologic cycle an lu 2.3.2.1 Climate nf va 2.3.2.2 Hydrology lm ul 2.3.3 Routing phase of the hydrologic cycle 10 oi 2.3.3.1 Routing in river 10 nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at v z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 2.3.3.2 Routing through reservoirs 10 2.3.3.3 Sediment routing 10 2.4 Component processes in model (Neitsch et al., 2005a) 11 2.4.1 Surface runoff 11 2.4.2 Underground Flow 13 2.4.2.1 Lateral subsurface flow 13 2.4.2.2 Underground flow 13 2.5 SWAT sediment component (Neitsch et al., 2005a) 14 2.5.1 The Modified Universal Soil Loss Equation (MUSLE) 14 Part 3: METHODS 16 3.1 Materials 16 3.1.1 Description and topography 16 3.1.2 Climatic characteristics 18 3.2 Methods 19 3.2.1 Watershed delineation 19 Lu an 3.2.2 Soil classification and soil physical characteristics 19 va n 3.2.3 Land cover classification 20 th ac 3.3 SWAT model 20 si nl w 3.4 SWAT model performance evaluation 22 d oa Part 4: RESULTS 25 an lu 4.1 Overview of Nghinh Tuong basin 25 nf va 4.2 Preparation input data 26 lm ul 4.2.1 Climatic parameters 26 oi 4.2.1.1 Precipitation 29 nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at vi z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 4.2.1.2 Stream discharge 31 4.2.2 Spatial databases 33 4.3 Land use scenarios 36 4.3.1 Baseline scenario (2012) 36 4.3.2 Scenario (2020) 37 4.3.3 Scenario (2030) 37 4.4 Assessing the impact of land-use changes on stream discharge in Nghinh Tuong watershed, Thai Nguyen Province 41 4.4.1 Baseline scenario 41 4.4.2 Land use scenario (2020) 45 4.4.3 Land use scenario (2030) 47 Part 5: CONCLUSIONS AND DISCUSSION 49 5.1 Conclusions 49 5.2 Discussion 50 REFERENCES 52 an Lu n va ac th si nl w d oa an lu oi lm ul nf va nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at vii z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 LIST OF TABLES Table 4.1 Summarized climatic characteristics (1983- 2012) of Nghinh Tuong watershed for SWAT simulation 27 Table 4.2 Total monthly precipitation in Nghinh Tuong watershed from 1983 to 2012.(mm) 30 Table 4.3 Observed monthly stream discharge at Nghinh Tuong outlet from 2002 - 2012 (m3/s) 32 Table 4.4 Sub-watershed characteristics of Nghinh Tuong watershed 35 Table 4.5 Sub-outlet’s characteristics of Nghinh Tuong watershed 36 Table 4.6 Land use scenarios for Nghinh Tuong watershed 39 Table 4.7 Observed and simulated stream discharge for each period in Nghinh Tuong watershed 42 Table 4.8 Coefficients of monthly NSE and PBIAS as calibrating and validating stream discharge 44 Lu an Table 4.9 Stream discharge of Scenarios (2020) and Baseline scenario in va n Nghinh Tuong watershed (m3/s) 46 th ac Table 4.10 Stream discharge of Scenarios (2030) and Baseline scenario in si nl w Nghinh Tuong watershed (m3/s) 47 d oa an lu oi lm ul nf va nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at viii z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 LIST OF FIGURES Figure 3.1: Map of Vo Nhai District 18 Figure 3.2 SWAT soil database builder schematization 20 Figure 3.3 Application of SWAT on Nghinh Tuong watershed for simulation stream discharge and sediment load 22 Figure 4.1: The position of Nghinh Tuong basin 25 Figure 4.2 Monthly maximum, minimum and average temperature in Nghinh Tuong watershed from 1983 to 2012 28 Figure 4.3 Monthly relative humidity in Nghinh Tuong watershed from 1983 to 2012 28 Figure 4.4 Monthly wind speed in Nghinh Tuong watershed from 1983 to 2012 29 Figure 4.5 Total monthly precipitation in Nghinh Tuong watershed from 1983 to 2012 31 Figure 4.6 Observed monthly stream discharge at Nghinh Tuong Lu an outlet from 2002 - 2012 32 va n Figure 4.7 Digital elevation model (DEM) and stream network of Nghinh Tuong th ac watershed 33 si nl w Figure 4.8 Map of land use status Nghinh Tuong River basin in 2012 34 d oa Figure 4.9 Soil map of Nghinh Tuong River basin in 2012 34 an lu Figure 4.10 Sub-watershed and stream network of Nghinh Tuong watershed 35 nf va Figure 4.11 Map of Baseline Land use scenario (2012) for Nghinh Tuong lm ul watershed 40 oi Figure 4.12 Map of Land use scenario 1(2020) for Nghinh Tuong watershed 40 nh 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37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Figure 4.13 Map of Land use scenario (2030) for Nghinh Tuong watershed 41 Figure 4.14 Observed versus simulated monthly stream discharge and precipitation of Nghinh Tuong watershed during calibration and validation periods 43 Figure 4.15 Observed versus simulated average monthly stream discharge during calibration and validation periods of Nghinh Tuong watershed 44 Figure 4.16 Locations of land use change for scenario (2020) for Nghinh Tuong watershed 45 Figure 4.17 Locations of land use change for scenario (2030) for Nghinh Tuong watershed 47 an Lu n va ac th si nl w d oa an lu oi lm ul nf va nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at x z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Figure 4.11 Map of Baseline Land use scenario (2012) for Nghinh Tuong watershed an Lu n va ac th si nl w d oa an lu lm ul nf va Figure 4.12 Map of Land use scenario 1(2020) for Nghinh Tuong watershed oi nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 40 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Figure 4.13 Map of Land use scenario (2030) for Nghinh Tuong watershed 4.4 Assessing the impact of land-use changes on stream discharge in Nghinh an Lu Tuong watershed, Thai Nguyen Province 4.4.1 Baseline scenario n va ac th The daily observed and simulated stream discharge were calculated si and summarized into mean wet season, mean dry season, and mean annual nl w Results from Table (4.7) indicate that the simulated data is lower than observed d oa data for both mean wet and dry season for calibration (2002-2012) For example, an lu mean wet and dry season of observed data were 24.85 and 5.13 (m3/s), while for va simulated data were 14.42 and 24.15 (m3/s), respectively oi lm ul nf nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 41 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Table 4.7 Observed and simulated stream discharge for each period in Nghinh Tuong watershed Calibration Validation Entire Period (2002-2007) (2008-2012) (2002-2012) Items Observed (m3/s) Mean annual Mean wet season 15 10.90 12.95 24.85 18.55 21.70 5.13 3.35 4.23 Mean dry season Simulated (m3/s) Mean annual 14.42 10.71 12.55 Mean wet season 24.15 18.35 21.24 Mean dry season 4.65 3.10 3.90 an Lu n va ac th si nl w d oa an lu oi lm ul nf va nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 42 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 an Lu n va ac th si nl w d oa lu an Figure 4.14 Observed versus simulated monthly stream discharge and va periods oi lm ul nf precipitation of Nghinh Tuong watershed during calibration and validation nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 43 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Table 4.8 Coefficients of monthly NSE and PBIAS as calibrating and validating stream discharge Simulation period Period Monthly NSE PBIAS (%) Calibration 2002 - 2007 0.76 6.54 Validation 2007 - 2012 0.87 4.74 Table 4.8 shows the results of the evaluation model through the NSE index PBIAS index quite good + Commissioning phase (2002-2007) NSE index = 0.76; PBIAS = 6.54 + Testing phase (2008-2012) NSE index = 0.87; PBIAS = 4.74 an Lu n va ac th si nl w d oa an lu ul nf va oi lm Figure 4.15 Observed versus simulated average monthly stream discharge nh during calibration and validation periods of Nghinh Tuong watershed 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 44 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Figure 4.15 illustrates that SWAT tends to underestimate stream discharge for major months of year The conceivable reason contributing to this result is the land use map generated based on year 2010 survey data which may cause differences in land use installed in the previous period Another reason causing discrepancy between simulated and observed sediment yield may be attributed to soil types 4.4.2 Land use scenario (2020) Stream discharge of Scenario results at Nghinh Tuong outlet were summarized in Tables 4.9, and Figure 4.16 an Lu n va ac th si nl w d oa an lu va Tuong watershed oi lm ul nf Figure 4.16 Locations of land use change for scenario (2020) for Nghinh nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 45 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Table 4.9 Stream discharge of Scenarios (2020) and Baseline scenario in Nghinh Tuong watershed (m3/s) Stream discharge (m3/s) Precipitation (mm) Items Baseline Scenario Baseline Scenario Difference Change Mean annual Scenario Scenario (%) 1698.0 1753.12 14.42 14.93 0.50 3.46 1390.2 1453.78 24.15 25.20 1.05 4.35 305.8 297.34 4.65 4.60 -0.05 -1.09 Mean wet season Mean dry season In general, stream discharge strongly depends not only on quantity of precipitation but also on land use change; high precipitation will lead to high stream discharge and land use change with increasing agricultural land will reduce stream discharge, especially in dry season an Lu In Mean wet season, precipitation increases 63.58 mm (4.57%) from va n 1390.20 mm in 2012 to 1453.78 mm in 2020 In this case, stream discharge in th ac 2020 is 25.20 m3/s, increases 1.05 m3/s (4.35%) in comparison with baseline si nl w scenario period However, in Mean dry season, stream discharge in 2020 d oa decreases 0.05 m3/s (1.09%) in comparison with baseline scenario period, from an lu 4.65 m3/s (2010) to 4.60 m3/s (2020) Meanwhile, precipitation decreases 8.46 nf va mm (2.77%) from 305.80 mm in 2010 to 297.34 mm in 2020 Therefore, mean with respect to baseline period oi lm ul annual of stream discharge just increases 3.46% (from 14.42 m3/s to 14.93m3 /s) nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 46 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 4.4.3 Land use scenario (2030) Figure 4.17 Locations of land use change for scenario (2030) for Nghinh Tuong watershed Table 4.10 Stream discharge of Scenarios (2030) and Baseline scenario in Nghinh Tuong watershed (m3/s) Baseline Scenario Baseline Scenario Difference Change Scenario 1698.0 1771.58 14.42 15.05 0.63 4.37 24.15 25.48 1.33 5.51 4.56 -0.09 -1.94 ac th n Scenario si Mean annual Stream discharge (m3/s) va Items an Lu Precipitation (mm) (%) nl w Mean wet 1478.26 305.8 291.32 lu 1390.2 an Mean dry oi lm ul nf 4.65 va season d oa season nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 47 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 Simulated result of Scenarios stated that stream discharge at mean wet season increases 1.33 m3/s (5.51%) from 24.15 m3/s (baseline period) to 25.48 m3/s (2030), while that at mean dry season decreases 0.09 m3/s (1.94%) from 4.65 to 4.56 m3/s (Table 4.10) One of the reasons of decreasing stream discharge in dry season is: when 1190.95 and 555.78 Forest-mixed land is converted into Agricultural land, especially Corn and Agricultural land-row crops which consume more water for cultivation Moreover, reducing forest land brings about decrease of ability for keeping and generating water within watershed an Lu n va ac th si nl w d oa an lu oi lm ul nf va nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 48 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 PART CONCLUSIONS AND DISCUSSION 5.1 Conclusions In this research, SWAT model was setup, calibrated and validated successfully at Nghinh Tuong watershed with the drainage area of 39700.58 In order to assess the impacts of land use change on stream discharge and sediment yield in Nghinh Tuong watershed, the land use scenarios were formulated combined with climate change in SWAT simulation In scenario 1, agricultural land (corn, orchard and tea) increases 786.08 (1.98%), meanwhile forest (forest-mixed) decreases 1091.77 (2.75%) as compared to baseline scenario Additionally, precipitation increases 3.74% in mean wet season, but decreases 0.5% in mean dry season with respect to baseline period In scenarios 2, agricultural land increases 1348.87 (3.39%) meanwhile forest decreases 1838.14 (21.41%) with respect to baseline scenario respectively Furthermore, precipitation increases 6.33% in mean wet season, but decreases 4.74% in mean dry season for scenario SWAT was able to simulate stream an Lu discharge and sediment yield for Nghinh Tuong watershed successfully not only for Baseline scenario but also for Scenario n va ac th During calibration process, sensitive parameters were identified as: CN2 (curve number), ESCO (soil evaporation compensation factor), EPCO (plant si uptake compensation factor), C FACTOR (cover and management factor) nl w d oa Simulation result for Baseline scenario showed a good agreement an lu between observed and simulated data SWAT shows its high capability in nf va stream discharge oi Spatial databases for SWAT model lm ul Through this research we have constructed Actiview database and nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 49 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 The results of running the model calculated stream discharge for the period (2002 - 2012) shows that Mean annual: 12,55 m3/s Mean wet season: 21.24 m3/s Mean dry season: 3.90 m3/s The results of the evaluation model through the NSE index PBIAS index quite good In brief, SWAT proves its ability in simulation stream discharge and sediment yield in watershed level It is a useful tool to assist water quantity and quality management process in Nghinh Tuong watershed 5.2 Discussion The Application of SWAT model is very large However, the input data requirements for models and need much time to process the data especially, maps like topographic maps, soil maps, forest maps and their attribute data To be able to use this model to quantitatively assess the impact of the floods forest Lu an necessarily have a uniform data input So that, the following time, we need to va n investigate basic data such as meteorology, climate, land, soil, hydrology, forest th ac etc to be able to put the model into more widespread use si nl w The model was validated for stream discharge and sediment yield at main d oa outlet, but not yet validated for sub-outlets due to the limited data Hence, the an lu validation process for stream discharge and sediment yield process at some important nf va sub-outlets must be done in the next step to ensure the validity of simulation lm ul In Nghinh Tuong watershed, when farmers cultivate agricultural crops, oi (especially in slope land) and apply pesticides and fertilizers for crops, which nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 50 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 make not only soil erosion but also pesticides and phosphorous load on stream into downstream However, there were no comprehensive assessments of pesticides loads in this river basin Hence, a modeling effort to simulate these problems in Nghinh Tuong watershed should be implemented in the near future an Lu n va ac th si nl w d oa an lu oi lm ul nf va nh 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.99 at 51 z z 37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.C.33.44.55.54.78.655.43.22.2.4.55.2237.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.55.77.77.99.44.45.67.22.55.77.C.37.99.44.45.67.22.66 REFERENCES Arnold, J G., J R Williams, and D R Maidment 1995 Continuous-time water and sediment-routing model for large basins Journal of Hydrology Engineering, ASCE 121(2): 171-183 Arnold, J G., R S Muttiah, R Srinivasan, and P M Allen 2000 Regional estimation of base flow and groundwater recharge in the upper Mississippi basin Journal of Hydrology 227(1-4): 21-40 Arnold, J G., R Srinivasan, T S Ramanarayanan, and M Di Luzio 1999 Water resources of the Texas gulf basin Water Science and Technology 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