Trung thesis 2005

AN APPLICATION OF SOIL AND WATER ANALYSIS TOOL (SWAT) FOR WATER QUALITY OF UPPER CONG WATERSHED, VIETNAM by Le Bao Trung A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering Examination Committee: Nationality: Previous Degree: Scholarship Donor: Dr Mukand Singh Babel (Chairman) Prof Ashim Das Gupta (Co-Chairman) Dr Roberto S Clemete Dr Sutat Weesakul Vietnamese Bachelor of Engineering in Hydrology and Environment Hanoi Water Resources University Hanoi Water Resources University MARD- WaterSpS - DANIDA Asian Institute of Technology School of Civil Engineering Thailand May 2005 i ACKNOWLEDGEMENTS The author wishes to express his sincere gratitude to his advisors, Dr Mukand Sigh Babel and Prof Ashim Das Gupta, for their advices, valuable suggestion and guidances Sincere thanks are also expressed to Dr Roberto S Clemete and Dr Sutat Weesakul for serving as as members of the thesis committee Grateful thanks are extended to Mr Hoang Thanh Tung, Ms Phung Thu Trang and Dr Nguyen Van Thang for their valuable datasets of this study Grateful acknowledgement is also due to the Hanoi Water Resources University, Ministry of Agriculture and Rural Development – the Government of Vietnam and DANIDA for the award of a scholarship and also Asian Institute of Technology for giving him the opportunity for this advanced study The author wants to express his sincere from the bottom of his heart for his friends for their supports, encourages and advices He also wants to express his intrinsic understanding of his family members, his beloved girlfriend for their unconditional loves ii ABSTRACT Under the rapid development of agricultural activities, water quality has become a serious problem in many watersheds of Vietnam Intensive agriculture has raised a public concern when huge amount of fertilizer and pesticides was used without proper management obviously making a severe impact to human health In this study, Soil and Water analysis Tool (SWAT) is used to simulate water quality problems in Cong watershed (Vietnam) Digital Elevation Model was obtained by United States Geologic Survey with resolution of 90 m Land cover was also obtained by Ministry of Agricultural and Rural Development of Vietnam (MARD) for years 1996, 1999, 2003 classified from LANDSAT images Digitized stream network and soil map (map scale 1:50000) were also obtained from MARD Meteorological data was collected from Ministry of Natural Resources and Environment of Vietnam (MONRE) Land operation and fertilizer information was provided by MARD and field surveys Rain fall data (six stations with recording duration from 1961-2003) were processed by using Integrated Quantity and Quality Model (IQQM) while a back-calculation process was implemented to estimate the natural inflow to the Nui Coc reservoir Baseflow filter was also used to determine the baseflow Results of calibration and validation show that the observed and simulated streamflow matches very well on monthly basis, quite reasonable on daily basis for both “natural” (1961 – 1970) and intensive agriculture condition (1994 – 2001) Sediment and nitrate yield maps were extracted from the long-term simulation results (1994 – 2001) SWAT simulation results suggested that sediment is not a severe problem with the watershed but nitrogen loads are the real threats Moreover, high concentration of ammonia endangered Thai Nguyen downtown residents in a relatively long period of time In brief, SWAT proved its ability in simulating the water quality problems in watershed level It is a useful tool to assist water quality management process in Cong watershed iii Table of contents CHAPTER 1.1 1.2 1.3 1.4 2.1 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.2 3.3 4.1 4.2 4.3 4.4 4.5 4.6 4.6.1 4.6.2 4.6.3 4.7 4.8 4.9 5.1 TITLE Title page Acknowledgement Abstract Table of Contents List of Tables List of Figures Acronym Introduction Problem Statement Rationale Objectives Scope of Study Literature Review Distributed Non-point source models Soil and Water Analysis Tool (SWAT) SWAT Theory SWAT climatic simulation SWAT hydrologic simulation SWAT sediment simulation SWAT nitrogen processes simulation Methodology Data treatment methods Topologic delineation Soil classification and soil physical characteristics Land cover classification Rainfall synchronization Runoff back-calculation and baseflow separation Irrigation water demand estimation Domestic and industrial water demand estimation SWAT (Soil and Water Analysis Tool) Evaluation of model prediction Study area and data collection Cong watershed description and its topography Soil characteristics and soil classification Land cover characteristics Fertilizers and management practices Reservoir data Hydrologic characteristics Rainfall Runoff Sediment Climatic characteristics Water demand Water quality Results and discussions Data treatment results iv PAGE i ii iii iv vi viii x 1 2 3 9 10 13 13 22 22 22 22 23 23 23 24 25 25 26 28 28 29 29 30 32 33 33 33 33 34 34 34 36 36 5.1.1 5.1.2 5.1.3 5.1.4 5.1.5 5.1.6 5.1.7 5.1.8 5.1.9 5.1.10 5.1.11 Climatic parameters Rainfall Reservoir data treatment and runoff back-calculation Runoff treatment and baseflow filter Sub-basin delineation and stream schematization Land cover classification, changes and assumptions Soil classificationand soil database development Derivation of domestic and industrial demand Irrigation demand Land operation and management assumptions Rainfall water quality Thai Nguyen surface water quality elementary 5.1.12 assessment 5.2 SWAT Calibration 5.2.1 SWAT model setup and land management scenarios 5.2.2 SWAT Cold Run 5.2.3 Water balance and stream flow calibration Impact of thresholds value for land use and soil 5.2.4 classification and simulation result 5.2.5 Flow Validation 5.2.6 Sediment calibration 5.2.7 Nutrient calibration 5.3 SWAT simulation for sediment and nutrient loads Summary, conclusions and recommendations 6.1 Summary and conclusions 6.2 Recommendations 6.3 Futher works References Appendix v 36 38 42 45 46 47 48 51 53 55 58 59 60 61 62 72 78 80 81 82 83 91 91 92 92 94 98 List of Table Table 2.1 Table 2.2 Table 3.1 Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 4.8 Table 4.9 Table 4.10 Table 4.11 Table 4.12 Table 4.13 Table 4.14 Table 4.15 Table 4.16 Table 4.17 Table 5.1 Table 5.2 Table 5.3 Table 5.4 Table 5.5 Table 5.6 Table 5.7 Table 5.8 Table 5.9 Table 5.10 Table 5.11 Table 5.12 Table 5.13 Table 5.14 Table 5.15 Table 5.16 Table 5.17 Table 5.18 Table 5.19 Table 5.20 Table 5.21 Table 5.22 Table 5.23 Table 5.24 TITLE Non-point source model applications Prominent SWAT applications in recent years Demand per capita for various country List of Soil types in Cau river basin Characteristics of some soil types in Cong watershed Land use statistics of Cong watershed in 1999 dataset Pesticides and fertilizers used in Thai Nguyen province Planted rice area and output in Thai Nguyen province in 2002 Maize and sweet potatoes planted area and outputs in Thai Nguyen Peanut and soybean planted area and outputs in Thai Nguyen Tea planted area and outputs in Thai Nguyen province in 2002 General parameters of Nui Coc Reservoir Dam structures of Nui Coc Reservoir Flood spillways and intake conduit of Nui Coc Rainfall Stations Stream gage stations Sediment characteristics of Thai Nguyen Irrigation area of Thai Nguyen and nearby province Irrigation demand volume of Thai Nguyen Annual Water quality control points Summarized climatic characteristics of Cong watershed Statistical characteristics of the four continuous recorded stations Comparison between Diem Mac and Yen Lang daily rainfall Filled years in rainfall records Statistical parameters of calculated and observed time series Temporal distribution of Cong watershed runoff characteristics Maximum observed discharges in Cong watershed Minimum observed discharge of Thai Nguyen Baseflow separation results Sub-basin characteristics of Cong watershed SWAT Land use code Soil classification translation and coding Saturated hydraulic conductivity and bulk density Soil type and its corresponding landuse in Cong watershed (unit Thai Nguyen sub-basin and equivalent Cong sub-basin Sub-basin population and domestic demand Industrial water demand of Thai Nguyen Crop intensity of Thai Nguyen province Calculated and statistical crop area Irrigation demand in each sub-basin of Cong river basin in 2000 Original P – factor values for contouring, strip-cropping, terraces Conservation P factor-assumed for SWAT simulation Paddy field storage characteristics Nutrients soil properties in Cong river basin vi PAGE 25 29 29 30 31 31 31 31 32 32 32 33 33 33 33 34 34 35 36 39 39 39 44 45 45 45 46 47 48 49 50 50 51 52 52 54 54 55 56 56 57 57 Table 5.25 Table 5.26 Table 5.27 Table 5.28 Table 5.29 Table 5.30 Table 5.31 Table 5.32 Table 5.33 Table 5.34 Table 5.35 Table 5.36 Table 5.37 Table 5.38 Table 5.39 Table 5.40 Table 5.41 Table 5.42 Table 5.43 Table 5.44 Table 5.45 Table 5.46 Table 5.47 Table 5.48 Table 5.49 Table 5.50 Applied fertilizer for land preparation in Spring (Jan – March) Applied fertilizer for tea Cropland operation assumed for SWAT simulation Tea land operation assumed for SWAT simulation Rainfall dataset for different simulation periods Hydrologic response unit characteristics Comparison between observed and calculated values – Cold Run Statistics of daily simulated and observed streamflow at Nui Coc Calculated sediment concentration at Tan Cuong station- Cold Run Statistics of monthly simulated NO3andNH4 concentration Statistics of daily simulated and observed monthly streamflow Statistics of monthly simulated sediment concentration in 1994-2002 Statistics of monthly simulated NO3 and NH4 concentration Statistics of daily simulated and observed value in 2001 Water balance calibration result Input used in water balance calibration Input used in daily flow calibration Statistics of calibrated and observed monthly streamflow Statistics of daily calibrated and observed value in 2001 Statistics of daily calibrated and observed value in 1994 - 2001 Statistics of simulated and observed daily streamflow in 2001 Final value after fine-tune calibration Statistics of daily validated and observed value in 2002 Value for sediment calibration Value for nutrient calibration Simulation results for long-term period 1990 - 2003 vii 57 57 58 58 62 62 65 66 66 68 69 70 71 72 73 73 74 74 75 78 79 80 80 81 82 84 List of Figures Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 Figure 3.1 Figure 3.2 Figure 4.1 Figure 4.2 Figure 4.3 Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9 Figure 5.10 Figure 5.11 Figure 5.12 Figure 5.13 Figure 5.14 Figure 5.15 Figure 5.16 Figure 5.17 Figure 5.18 Figure 5.19 Figure 5.20 Figure 5.21 Figure 5.22 Figure 5.23 Figure 5.24 Figure 5.25 Figure 5.26 Figure 5.27 Figure 5.28 Figure 5.29 Figure 5.30 Figure 5.31 Figure 5.32 Figure 5.33 Figure 5.34 Figure 5.35 TITLE SWAT information layers and results Conceptualization of SWAT model (MRC, 2004) Muskingum method explanations Nitrate cycle in watershed SWAT soil nitrogen pools and processes Nitrogen cycle in natural waters Linkage of FAO Soil Classification to Hydrologic Soil Group SWAT soil database builder schematization Cong watershed location on Vietnam map Cong watershed land cover datasets in 1996 and 1999 Rainfall, runoff gauges and water quality monitoring points in Cong Thai Nguyen downtown station – Monthly wind speed Monthly Maximum, Minimum and Average daily temperature Thai Nguyen Station – Monthly relative humidity Thai Nguyen piche evaporation Phu Ho station – Monthly solar radiation from 1997 - 2001 Synchronization between Diem Mac and Ky Phu Filling the missing rainfall records at Diem Mac station Frequency analysis of Diem Mac daily rainfall data Regression analysis between Diem Mac daily rainfall data Regression analysis between Minh Tien daily rainfall data Frequency analysis between Minh Tien daily rainfall data Frequency analysis of four rainfall stations Water level and Volume relationship and water level at Nui Coc Total outflow of Nui Coc reservoir Calculated and smoothed inflow of Nui Coc reservoir in 2002 Frequency analysis between calculated inflow and gauged runoff Comparison between calculated and observed runoff Baseflow separation result at Nui Coc Cong watershed topography and sub-basin delineation Cong watershed land use distribution after classification Cong watershed soil distribution after classification Soil and its corresponding landuse of Cong river basin Thai Nguyen sub-basin and equivalent Cong sub-basin Population distribution in sub-basin in Thai Nguyen province Irrigation zones of Thai Nguyen province Crop area in Cong watershed – detailed classification Estimated irrigation demand in 2000 at Cong river basin Terraced- ponding cultivation system in Thai Nguyen NO3and NH4 concentration of rainfall water in Thai Nguyen DO concentration at Nui Coc in 2003 NO3 concentration in Cong River from upstream to downstream NH4 concentration in Cong River from upstream to downstream Upstream Cong watershed sub-basin schematizations Runoff results of TAN CUONG Station – Cold Run 1961 -1970 Relationship and runoff frequency analysis viii PAGE 10 11 14 14 19 22 23 28 30 35 37 37 37 38 38 39 40 40 40 41 41 42 42 43 43 44 44 45 46 48 49 50 51 52 53 54 55 56 59 59 60 60 61 63 64 Figure 5.36 Figure 5.37 Figure 5.38 Figure 5.39 Figure 5.40 Figure 5.41 Figure 5.42 Figure 5.43 Figure 5.44 Figure 5.45 Figure 5.46 Figure 5.47 Figure 5.48 Figure 5.49 Figure 5.50 Figure 5.51 Figure 5.52 Figure 5.53 Figure 5.54 Figure 5.55 Figure 5.56 Figure 5.57 Figure 5.58 Figure 5.59 Figure 5.60 Figure 5.61 Figure 5.62 Figure 5.63 Figure 5.64 Figure 5.65 Figure 5.66 Figure 5.67 Figure 5.68 Figure 5.69 Figure 5.70 Figure 5.71 Figure 5.72 Figure 5.73 Figure 5.74 Runoff results of Nui Coc– Cold Run 1994 – 2002 (natural condition) Relationship and frequency analysis of observed runoff and calculated runoff at Nui Coc – Cold Run 1994 – 2002 (natural condition scenario) Daily simulated and observed streamflow at Nui Coc in 2001 Frequency analysis and relationship of observed and calculated daily runoff at Nui Coc– Cold Run 2001 (natural condition scenario) Sediment concentration – observed and calculated value Relationship between observed and calculated value – Cold Run NO3 and NH4 concentration at Nui Coc in 1961-1970 – Cold Run Monthly simulated and observed streamflow at Nui coc 1994 – 2002 Frequency analysis and relationship of monthly streamflow Sediment concentration in Nui Coc – 1994 – 2002 Nitrogen concentrations at Nui Coc - 1994 – 2002 Daily simulated and measured at Nui Coc in 2001 Frequency analysis and relationship of observed and calculated daily runoff at Nui Coc– Cold Run in 2001 –( Intensive Agriculture scenario) Calibrated and observed runoff at Nui Coc 1994 – 2001 Frequency analysis and relationship of calibrated and observed monthly runoff at Nui Coc 1994-2001 Calibrated and observed daily runoff at Nui Coc - 2001 Frequency analysis and relationship of calibrated and observed daily runoff at Nui Coc -2001 Observed and simulated daily stream flow at Nui Coc 1994 - 1996 Observed and simulated daily stream flow at Nui Coc 1997 - 1999 Observed and simulated daily stream flow at Nui Coc 2000 - 2001 Frequency analysis and correlation between observed and simulated Simulated and observed daily runoff at Nui Coc – 2001 Frequency analysis and relationship between simulated and observed daily runoff at Nui Coc -2001 Validated and observed daily runoff at Nui Coc - 2002 Frequency analysis and relationship of validated and observed daily runoff at Nui Coc -2002 Observed and simulated sediment concentration at Nui Coc Observed and simulated nitrate concentration at Nui Coc Observed and simulated ammonia concentration at Nui Coc Temporal distribution of ranfall runoff, lateral flow, total water yield and evapotranspiration as presented in depth (mm) on the upstream of Nui Coc Spatial surface and total water yield distribution in upstream Nui Coc Total water yields in each sub-basin Annual sediment yield and corresponding land use of each sub-basin Sediment yield of sub-basin 1, 2, 3, 4, from 1990 to 2003 Erosion from different land use type Total nitrogen and organic nitrogen yield transported with surface flow Nitrogen loads transported with surface water to the reach at each subbasin Organic nitrogen transported with surface water to the reach Nitrate yield from different land use Nitrate and organic N yield in each HRU of upstream Cong watershed ix 64 64 65 66 67 67 68 69 69 70 70 71 71 75 75 76 76 76 77 77 78 79 79 80 81 82 83 83 85 85 86 86 87 87 88 88 89 89 90 ACRONYM ASAE BMP BOD CRBC DO Ens FRSE ARGL RNGE RNGE HRU IAN1 IFPM IQQM MARD MONRE MUSLE MRC NHIC NMRSE NSA R2 SWAT USGS USLE USEPA American Society of Agricultural Engineers Best Management Practice Biological Oxygen Demand Cau River Basin Committee Dissolved Oxygen Nash – Sutcliffe Efficiency Forest Evergreen Generic Agriculture Land Rangeland Rangeland Brush Hydrologic Response Unit Institute for Aquaculture No.1 Institute of Forest Planning and Management Integrated Quantity and Quality Modeling Ministry of Agriculture and Rural Development Ministry of Natural Resource and Environment Modified Universal Soil Loss Equation Mekong River Committee National Hydrologic Institute Normal Root Mean Square Error National Statistical Agency Correlation coefficient Soil and Water Analysis Tool United States Geologic Survey Universal Soil Loss Equation United States Environmental Protection Agency x Average monthly values for upstream of Nui Coc reservoir in 1990 - 2003 400 350 Runoff 300 Lateral flow Water yield Evapo-trans RAIN mm 250 200 150 100 50 Jan Feb Mar Apr May Jun Jul Month Aug Sep Oct Nov Dec Figure 5.64: Temporal distribution of ranfall runoff, lateral flow, total water yield and evapotranspiration as presented in depth (mm) on the upstream of Nui Coc Figure 5.65: Spatial surface and total water yield distribution in upstream Nui Coc 85 Figure 5.66: Total water yields in each sub-basin Figure 5.67: Annual sediment yield and corresponding land use of each sub-basin 86 Figure 5.68: Sediment yield of sub-basin 1, 2, 3, 4, from 1990 to 2003 Sediment yield from different land use Sediment yield (tonne/ha) 2.5 1.5 0.5 FRSE RICE Figure 5.69: Erosion from different land use type 87 Tea Figure 5.70: Total nitrogen and organic nitrogen yield transported with surface flow to the reach in upstream Nui Coc Figure 5.71: Nitrogen loads transported with surface water to the reach at each sub-basin 88 Figure 5.72: Organic nitrogen transported with surface water to the reach at each sub-basin Nitrate yield of each land use (kg/ha) 72.56 80.00 60.00 FRSE 40.00 20.00 RICE 12.25 6.31 0.00 FRSE RICE TEA Figure 5.73: Nitrate yield from different land use 89 TEA Nitrate & organic N loads in each HRU 400 Load (kg/ha/year) 350 OrganicN (kg/ha) NO3 Kg/ha 300 250 200 150 100 50 10 11 12 13 14 15 16 17 18 19 20 HRU Figure 5.74: Nitrate and organic N yield in each HRU of upstream Cong watershed 90 CHAPTER 6: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 6.1 Summary and Conclusion In this research, SWAT model was setup, calibrated and validated successfully at upper part of Cong watershed with the drainage area of 535 km2 Digital Elevation Model was provided by United States Geologic Survey agency with resolution of 90 m Land cover was provided by Ministry of Agricultural and Rural Development (MARD) for years 1996, 1999, 2003 with the classification from LANDSAT images Digitized stream network and Soil Map was also obtained from MARD (equivalent map scale 1:50000) Meteorological data was obtained from Ministry of Natural Resources and Environment (MONRE) Land operation and fertilizer information was provided by MARD and field surveys Rain fall data was processed by using Integrated Quantity and Quality Model (IQQM) while a back-calculation process was implemented to estimate the natural inflow to Nui Coc reservoir (at the outlet of upper Cong watershed) Baseflow filter was also used to estimate baseflow (Arnold, 1999) The entire watershed was divided into sub-basins under threshold area for stream definition of 5700 SWAT simulation was implemented with the threshold value for land use and soil varies from 1% to 20% which result from 20 to 83 HRUs Results from calibration process show very fitted between observed and simulated results on monthly basis (R2 = 0.89, Nash – Sutcliffe Efficiency = 0.75) and quite acceptable on daily basis (R2 = 0.83, Nash – Sutcliffe Efficiency = 0.6) for both “natural” period (1961 – 1970) and intensive agriculture period (1994 – 2001) Daily calibration result for the entire period (1994 – 2001) gives reasonable results with R2 = 0.72 and Nash – Sutcliffe Efficiency = 0.48 Validation for stream flow simulation assure the simulation result in the year 2002 on daily basis (R2 = 0.86, Nash – Sutcliffe Efficiency = 0.55) SWAT shows its high capability in sediment and nitrogen loads simulation with the NRMSE is mostly less than (NRMSE = 0.68 for sediment and NRMSE = 0.89 for nitrate concentration) Water quality verification is the limitation of the model due to the data availability However, the new established monitoring system in Cong watershed will provide sufficient water quality data and it guarantees the validity of the model Sediment and nitrate yield maps were extracted from the long-term simulation results (1994 – 2001) The highest sediment and nitrogen yield locations (sub-basin and 4) are indicated The following conclusions can be withdrawn: 1) Soil characteristics determine all simulation results 2) Muskingum routing is suitable for Cong watershed but Variable storage routing is not suitable for Cong watershed 3) Sediment is not the real problem to Nui Coc reservoir 4) Nutrient is the severe problem (highest peak of ammonia concentration can reach mg/L which can severely affect human health) 5) Sediment and nutrient mostly come from paddy fields Spatial rainfall distribution played a decisive factor on daily stream flow simulation SWAT allows only one rainfall station in one sub-basin Consequently, the determination of sub-basin and its corresponding rainfall station (spatial rainfall distribution) is the key factor for streamflow simulation Results also show that soil characteristics have higher effects than crop management practice in sediment and nutrient simulation Unfortunately, soil information was poorly investigated in the field by experiment in this study It obviously affected much on the simulation results 91 The model shows better results in some cases in comparison with recent SWAT researches (Barsanti, 2003; White, 2001; Saleh et al, 2001; Gassmma et al 2003) Simulation shows a fit result in the period 1961-1970 and 1994 – 2001 due to rainfall data availability: the enormously continuous recorded rainfall (six stations available) Error increases when the number of recording stations reduces (four stations in 2002) and especially in 2003 (with only two stations) In brief, SWAT proved its ability in simulation the water quality problems in watershed level It is a useful tool to assist water quality management process in Cong watershed 6.2 Recommendations More detailed topography of Cong watershed should be provided (finer resolution of 30m); detailed crop management and land practices must be further investigated to improve the simulation results In this research a high threshold value (rough delineation) for stream definition was defined (5700ha) due to study time limitation Therefore, a finer threshold value must be defined up to 20ha (Romanowicz, 2005; Grizzetti, 2003; Tolson and Shoemaker, 2004) which results larger number of sub-basins and obviously promises more accurate simulation results However, the lower value of threshold value for stream definition only increased the accuracy of model simulation to a certain point (Romanowicz, 2005) Therefore, this threshold value should be examined under calibration process In this research, spatial rainfall distribution was determined by empirical method as well as calibrating The need of in-depth research which determines the weight of each gauge by Theisson polygon is then necessary to be completed The model was not validated for water quality components due to the limitation in water quality data Hence, the validation process for sediment and nutrient process must be done in the next step to ensure the validity of simulation The monitoring system in Cong watershed has been established for years and it will provide more available information in the next few years which assists the management process The big reservoir as Nui Coc cannot be modeled directly due to the well-mixed assumption of QUAL2E model Therefore, a careful modeling effort should be carried out in the downstream of Nui Coc reservoir (where the agriculture is extremely intensive with high irrigated areas) Pesticides and phosphorous problems are the real threats to Nui Coc reservoir according to MONRE survey in 2002 However, there were no comprehensive assessments of pesticides loads in this river basin Hence, a modeling effort to simulate these problems in Cong watershed should be implemented in the near future Because of the fact that rainfall contributes significant natural nitrogen for this area (23 kg / ha/ year) the concentration of nitrate in rainfall must be examined carefully However SWAT does not have a mechanism for using recorded rainfall water quality by time steps and it should be recommend for the developers to add it Best Management Practice (BMP) was not examined carefully due to time constraints However, SWAT indicates that BMP existence is realistic and it is recommended to be further investigated in in-depth studies 6.3 Further works The impact of agriculture on environment in this region is severe However, there were no proper studies focusing on pesticides transport and phosphorus loading in this region It is the case that Nui Coc reservoir supplying for 200,000 people in the downtown 92 and water quality is the most concerned problem in the area Consequently, the following works should be implemented: ‰ Improving the spatial rainfall distribution ‰ Adding point sources nutrient loads ‰ Validating the water quality component ‰ Pesticides transport (surface and river routing) ‰ Phosphorus loading ‰ Best Management Practice should be investigated 93 REFERENCES Albek M., Ogutveren B., Albek E (2003) Hydrological modeling of Seydi Suyu watershed (Turkey) with HSPF Journal of Hydrology ,285(2004), 260–271 Anderson R (1976) A Land Use and Land Cover Classification System for Use with Remote Sensor Data Geological Survey Professional Paper 964, 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transplant June Oct Early rice Apr - May Sow Apr, June - Jul August transplant May - June Spring Maize Jan Jan Feb- Mar Apr Summer – autumn June June Jul-Aug Oct maize Spring soybean Jan Jan Feb-Mar Apr Summer-autumn Jun Jun Aug Late Sept soybean Sugar cane Jan - Feb Jan - Feb Mar, Apr, Nov,Dec, Jan May, Jun Cassava Feb Feb Mar - May Oct, Nov, Dec Taro Oct, Nov, Dec Oct, Nov, Dec Feb-Mar May -Jun Peanut Jan - Feb Jan -Feb Feb-Mar Apr –May Chiem peanut Jun Jun Jul -Aug Oct Tea Jul - Aug Aug All year Jan - Oct around Vegetable Oct- Dec Oct -Dec Oct-Dec Oct-Dec Source: Institute for Aquaculture No.1 survey Table A - Cropping pattern in Phuong Tien Commune – Thai Nguyen province Plant Land Sowing and planting Care taking Harvest preparation Winter- spring rice Late Jan Sow Jan, transplant Mar-Apr Late Jun Feb Feb-March Early rice Early Jul Sow early Jun, Jul -Sep Late Sep – Oct transplant Jul Summer – autumn Jul Sow early May, Jul, Aug, Sep Mid-late Nov rice Transplant May- Jun Spring maize Feb Feb Mar-Apr May Summer-autumn Jun Jun Jul-Aug Sep maize Winter maize Sep Sep Oct- Nov Dec –Jan Sweet - potato Sep-Oct Sept-Oct Oct-Nov Dec-Jan Cassava Feb-Mar Feb-Mar Apr, May, Jun, Oct-Dec Jul Tea Oct-Nov Oct-Nov All year around All year around Winter vegetables Aug- Sep Aug-Sep Oct- Nov Oct- Nov -Dec Source: Institute for Aquaculture No.1 survey (2001) 98 Table A Sub-basin 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Mean Table A - Yearly sediment yield from each sub-basin (unit : tonne/ha/year) 0.861 0.096 0.317 0.494 0.102 1.26 0.016 0.453 0.119 0.096 1.39 0.08 0.361 0.253 0.076 0.419 0.099 0.269 0.222 0.094 1.26 0.165 0.466 0.435 0.175 1.36 0.113 0.43 0.418 0.093 2.78 0.194 0.57 0.676 0.155 0.992 0.138 0.489 0.387 0.139 0.52 0.051 0.211 0.136 0.087 0.666 0.047 0.253 0.151 0.096 4.14 0.142 0.362 0.371 0.103 4.25 0.163 0.606 0.638 0.137 0.466 0.073 0.264 0.179 0.102 1.24 0.247 0.444 0.739 0.149 1.54 0.116 0.392 0.372 0.114 4Average annual simulated results for each HRU in upstream Nui Coc Sediment NO3 OrganicN Land Area Yield yield yield Biomass Yield HRU SUB Cover Soil (km2) T/ha Kg/ha (kg/ha) (t/ha) (t/ha) 1 RNGB Dystric Cambisol 30.80 0.1 9.94 1.59 13.53 4.4 RNGB Leptosol 14.90 0.07 13.1 1.95 RICE Eutric Fluvisol 9.95 10.34 26.3 206.47 6.51 2.6 RICE Dystric Cambisol 17.10 0.3 31.32 4.01 6.51 2.6 RNGB Dystric Cambisol 28.70 0.07 3.61 0.12 10.75 3.5 RNGB Haplic Acrisol 13.40 0.06 5.52 0.07 9.84 3.2 RNGB Dystric Cambisol 13.70 0.07 5.87 0.89 13.53 4.4 RNGB Leptosol 39.90 0.06 6.22 6.36 2.07 RICE Haplic Acrisol 22.50 0.34 25.88 2.06 6.47 2.58 10 RICE Haplic Acrisol 19.30 0.11 51.55 0.6 6.47 2.58 11 RNGB Dystric Cambisol 71.40 0.14 10.76 1.92 13.61 4.43 12 RNGB Ferralic Cambisol 35.50 0.16 9.71 0.04 9.67 3.15 13 RICE Dystric Cambisol 103.00 0.65 8.54 4.69 6.46 2.58 14 RNGB Dystric Cambisol 6.69 0.13 25.78 0.02 8.2 2.67 15 RNGB Leptosol 15.60 0.05 30.16 4.13 1.34 16 FRSE Leptosol 14.90 0.06 6.31 3.03 1.77 17 RICE Eutric Fluvisol 7.02 2.24 1.71 34.7 6.53 2.6 18 RICE Regosols 19.40 0.28 362.62 0.12 6.53 2.6 19 RNGB Dystric Cambisol 21.20 0.16 11.57 1.21 14.01 4.56 20 RNGB Leptosol 25.50 0.07 14.81 4.9 1.59 99 ... and Shoemaker, 2003; Romanovicz, 2005) Moreover, the development of input data treatment methods is being considered (Tolson and Shoemaker, 2004; Chaplot et al, 2005) The most valuable researches... glucose to carbon dioxide and water is used for various cell processes, including protein synthesis Protein synthesis requires nitrogen If the residue from which the glucose is obtained contains enough... from very small basin (22 km2 – Bosch, 2004), small basin (212 km2 – Neitsch, 2002; Romanovicz, 2005) to medium basin (1115 km2, Tolson and Shoemaker, 2004) and large basin (15200 km2 Barsanti,