IN-STREAM WATER QUALITY PROCESSES IN SWAT

Transcription

1 MSc thesis presentation IN-STREAM WATER QUALITY PROCESSES IN SWAT Linh Hoang, Ann van Griensven, Jan Cools, and Arthur Mynett 2009 International SWAT conference, SWAT August 5-7, 2009, Boulder, Colorado 1

2 Water quality processes in SWAT CATCHMENT MODELLING 1. INTRODUCTION Change from focusing on the control of point sources of pollution to setting water quality objectives for the receiving water Integrate all water quality issues both point and diffuse pollution sources at river basin scale RIVER WATER QUALITY MODELLING Need to include a proper water quality module in SWAT Validated with SOBEK and WEST models 2

3 1. INTRODUCTION Data of point source pollutant loads CATCHMENT MODELLING estimate the flows of water and pollutants released from draining catchment into the receiving water SWAT RIVER WATER QUALITY MODELLING Model the pollutant transport and water quality along the river (receiving water) WEST SOBEK SWAT 3

4 1. INTRODUCTION RIVER WATER QUALITY MODEL SWAT WEST SOBEK Hydraulic routing - Muskingum method - Variable storage method + Adapted routing method Water quality QUAL2E Hydraulic routing Continuous stirred Tank Reactors in series Water quality RWQM1 Hydraulic routing 1D Saint Venant equation Water quality DELWAQ 4

5 3. STUDY AREA: Grote Nete basin Pollution sources WWTPs Industry Agriculture Households 5

6 3. STUDY AREA: Grote Nete basin SWAT model of Grote Nete river basin (calibrated on flow, water quality: not calibrated) + 14 subbasins (1 point source/subbasin) + 71 HRU 6

7 3. STUDY AREA: Grote Nete basin Data of point sources ( households, industry, WWTP, agriculture point sources): Data of diffuse source ( fertilizer applied including chemical fertilizer and animal manure) : Water quality data (2 points on the river used for calibration): Variables used to calibrate: NO 3, NO 2, NH 4, PO 4, DO, BOD

8 Routing/in-stream processes in SWAT SWAT with WEST routing SWAT with SOBEK routing 8

9 4. Routing/in-stream processes in SWAT New routing module ( Manning ) Independent on time step Based on Manning equation to calculate velocity, storage, depth. New water quality module Independent on time step Original process applied on output (Conc_output=conc*process rate * residence time) Processes applied IN REACH (Conc_t2= conc_t1*process rate * calculation time step) 9

10 4. Routing/in-stream processes in SWAT Routing method used: Muskingum mg/l orgn Outflow_with processes Outflow_without processes flow Day Flow (m3/s) Residence time < time step When inflow decrease, outflow is possibly bigger than inflow no storage in the reach no WQ processes implemented 10

11 4. Routing/in-stream processes in SWAT Storage not correctly calculated with Variable storage and Muskingum: new routing module based on manning equation Storage in reach m3 2.E+06 2.E+06 2.E+06 1.E+06 1.E+06 1.E+06 8.E+05 6.E+05 4.E+05 2.E+05 0.E Variable Storage Muskingum manning 11

12 4. Routing/in-stream processes in SWAT Routing method used: adapted Manning routing method This method has distinct equations for 2 situations when residence time is bigger and smaller than time step There is always water stored in the reach WQ processes are always implemented. 2 orgn Outflow_with processes Outflow_without processes 1.5 mg/l Day 12

13 2. CALIBRATION Parameter used to calibrate (chosen from result of sensitivity analysis) and their final value BIOMIX Biological mixing efficiency 0 NPERCO Nitrogen percolation coefficient rs4 Rate coefficient for organic N settling in the reach at 20 o C [day-1] rs5 Organic phosphorus settling rate in the reach at 20 o C [day-1] 1 rk1 rk2 rk3 Carbonaceous biological oxygen demand deoxygenation rate coefficient in the reach at 20 o C [day-1] 1 Oxygen reaeration rate in accordance with Fickian diffusion in the reach at 20 o C [day-1] Rate of loss of carbonaceous biological oxygen demand due to settling in the reach at 20 o C [day-1] 1 bc1 Rate constant for biological oxidation of NH4 to NO2 in the reach at 20 o C [day-1] bc2 Rate constant for biological oxidation of NO2 to NO3 in the reach at 20 o C [day-1] bc3 Rate constant for hydrolysis of organic N to NH4 in the reach at 20 o C [day-1] 0 bc4 4. Routing/in-stream processes in SWAT Rate constant for mineralization of organic P to dissolved P in the reach at 20 o C [day-1]

14 4. Routing/in-stream processes in SWAT 2. CALIBRATION Result of calibration NO3 measured simulated 5 NO3 (g/s) NO 3 measured simulated NO3 (mg/l) Rank measured NO3 simulated /1/02 1/1/03 1/1/04 1/1/05 1/1/06 Time NO3 (mg/l) /01/ /02/ /03/ /04/2005 Time 20/05/2006

15 4. Routing/in-stream processes in SWAT 2. CALIBRATION Result of calibration PO4 0.5 measured PO4 simulated 0.5 simulated PO4 measured PO4 (mg/l) PO4(mg/l) Rank /01/ /02/ /03/ /04/ /05/2006 Time 15

16 Routing/in-stream processes in SWAT SWAT with WEST routing SWAT with SOBEK routing 16

17 5. SWAT with WEST routing WEST model of a reach of Grote Nete river (calibrated both on flow and water quality) 17

18 5. SWAT+WEST Integrated model SWAT-WEST in5 + sub5 1 4p + out1 + sub3 3 5p + sub4 WEST river model: Input nodes 3 input nodes for diffuse souces which are taken from SWAT 6 input nodes for point souces Flow model: 10 tanks in series Water quality model: simplified RWQM1 with 16 processes and 16 variables 2 18

19 6. SWAT+WEST Integrated model SWAT-WEST Output of SWAT Flow NO3 NH3 NO2 MinP DO Directly transfer, only change unit Input of WEST H2O S_NO3 S_NH S_NO2 S_PO S_O2 CBOD /COD_OM_S_S *f_bod_cod/cod_om_s_i S_S S_I X_S X_I *1.5 *1.5 CHLA *α 0 X _ALG From calibration X_H X_N1 X_N2 X_P XII 19

20 Routing/in-stream processes in SWAT SWAT with WEST routing SWAT with SOBEK routing 20

21 6. SWAT+SOBEK Integrated model SWAT-SOBEK SOBEK river model: Input nodes 2 boundary nodes: + Upstream: discharge + Downstream: water level 8 lateral flow nodes 21 cross sections Flow model: 1D Saint Venant 4p+out1 +sub3 5p + sub4 Boundary condition equation with dx=100m 2 Water quality model: predefined process Oxygen and Nutrients 3 5 Lateral flow 4 Cross section 21

22 7. RESULT AND DISCUSSION 22

23 COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK Water routing Downstream boundary Upstream boundary Flow (m3/s) Outflow chosen to compare SOBEK SWAT WEST 0 1/1/2002 1/16/2002 1/31/2002 2/15/2002 3/2/2002 3/17/2002 4/1/2002 4/16/2002 Day 23

24 COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK SWAT NH4 WEST SOBEK Loss Nitrification to NO2 Growth of 1 st stage nitrifier Aerobic Growth of heterotrophs Nitrification Gain Mineralization from orgn Diffusion from sediment Respiration of organisms Mineralization from detn 2.5 NH4 Result fromsobek Result from SWAT Result from WEST 2 mg/l /1/2002 7/1/2002 1/1/2003 7/1/2003 1/1/2004 7/1/2004 Date 1/1/2005 7/1/2005 1/1/2006 7/1/

25 COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK NO3 SWAT WEST SOBEK Loss Anoxic growth of heterotrophs Aerobic Growth of heterotrophs Denitrification Gain Nitrification to NO3 Diffusion from sediment Growth of 2 nd stage nitrifiers Nitrification of NH4 4 NO3 Result from SOBEK Result from SWAT Result from WEST 3 mg/l /1/2002 7/1/2002 1/1/2003 7/1/2003 1/1/2004 7/1/2004 Date 1/1/2005 7/1/2005 1/1/2006 7/1/

26 COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK SWAT PO4 WEST SOBEK Loss Growth of heterotrophs Growth of nitrifiers Adsorption to inorganic matter Gain Mineralization from orgp Diffusion from sediment Respiration of organisms Mineralization from detp 0.6 Result from SOBEK Result from WEST PO4 Result from SWAT measured value 0.4 mg/l /1/2002 7/20/2002 2/5/2003 8/24/2003 3/11/2004 9/27/2004 Date 4/15/ /1/2005 5/20/ /6/2006

27 COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK SWAT CBOD WEST SOBEK Loss Decay of OM Settling to sediment Growth of heterotrophs Decay of OM Settling to sediment Gain Hydrolysis 8 CBOD Result from SOBEK Result from SWAT Result from WEST 6 mg/l /1/2002 7/1/2002 1/1/2003 7/1/2003 1/1/2004 7/1/2004 Date 1/1/2005 7/1/2005 1/1/2006 7/1/

28 COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK Loss SWAT DO WEST SOBEK Nitrification Growth of nitrifiers Nitrification Decay of OM Growth of heterotrophs Decay of OM SOD Respiration of organisms Gain Aeration Aeration Aeration DO 15 Result from SOBEK Result from SWAT Result from WEST 12 mg/l /1/2002 7/1/2002 1/1/2003 7/1/2003 1/1/2004 7/1/2004 Date 1/1/2005 7/1/2005 1/1/2006 7/1/

29 8. CONCLUSION AND RECOMMENDATION CONCLUSION Muskingum and newly adapted routing methods in SWAT give different effect for instream water quality processes. The adapted routing method gives logical results for water quality because there is always water stored in the reach in this method Comparison between different river water quality models SWAT, WEST and SOBEK For water routing, the 3 models give quite similar result The trend and value of orgn, orgp, NH4, NO3, CBOD, DO are quite similar in SWAT, WEST and SOBEK The result of PO4 is very different in the 3 models because of the addition of processes to reduce PO4 in WEST and SOBEK (growth of nitrifiers and heterotropic bacteria in WEST and adsorption to sediment in SOBEK) Adsorption process is possibly an important process that has to be included for proper PO4 modelling. 31

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