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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
MSc thesis presentation
2
CATCHMENT MODELLING
RIVER WATER QUALITY MODELLING
Water quality processes in SWAT 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
1. INTRODUCTION
⇒Need to include a proper water quality module in SWAT⇒ Validated with SOBEK and WEST models
3
CATCHMENT MODELLING
estimate the flows of water and pollutants
released from draining catchment into the
receiving water
RIVER WATER QUALITY MODELLING
SWAT
Data of point source pollutant loads
Model the pollutant transport and water
quality along the river (receiving water)
WEST SOBEKSWAT
1. INTRODUCTION
4
Hydraulic routing- Muskingum method- Variable storage
method+ Adapted routing
methodWater qualityQUAL2E
SWAT
Hydraulic routing1D Saint Venant equation
Water qualityDELWAQ
SOBEKWEST
Hydraulic routingContinuous stirred Tank Reactors in series
Water qualityRWQM1
RIVER WATER QUALITY MODEL
1. INTRODUCTION
5
3. STUDY AREA: Grote Nete basin
Pollution sources
Agriculture Households
WWTPs
Industry
6
SWAT model of Grote Nete river basin (calibrated on flow, water quality: not calibrated)
+ 14 subbasins (1 point source/subbasin)
+ 71 HRU
3. STUDY AREA: Grote Nete basin
7
Data of point sources ( households, industry, WWTP, agriculture point sources): 1998-2006
Data of diffuse source ( fertilizer applied including chemical fertilizer and animal manure) : 1998-2006
Water quality data (2 points on the river used for calibration): 2002-2006. Variables used to calibrate: NO3, NO2, NH4, PO4, DO, BOD5
25300
25500
3. STUDY AREA: Grote Nete basin
8
Routing/in-stream processes in SWAT
SWAT with WEST routing
SWAT with SOBEK routing
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)
10
orgN
00.5
11.5
22.5
33.5
44.5
1 46 91 136 181 226 271 316Day
mg/
l
0
5
10
15
20
25
30
Flow
(m3/
s)
Outflow_with processesOutflow_without processesflow
Routing method used: Muskingum
Residence time < time step When inflow decrease, outflow is possibly bigger than inflow no storage in the reach no WQ processes implemented
4. Routing/in-stream processes in SWAT
11
Storage in reach
0.E+002.E+054.E+056.E+058.E+051.E+061.E+061.E+062.E+062.E+062.E+06
1 229 457 685 913 1141 1369 1597 1825
m3
Variable StorageMuskingummanning
Storage not correctly calculated with Variable storage and Muskingum: new routing module based on manning equation
4. Routing/in-stream processes in SWAT
12
Routing method used: adapted Manning routing method
orgN
0
0.5
1
1.5
2
1 46 91 136 181 226 271 316Day
mg/
l
Outflow_with processesOutflow_without processes
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.
4. Routing/in-stream processes in SWAT
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 0.1655
rs4 Rate coefficient for organic N settling in the reach at 20oC [day-1] 0.6845
rs5 Organic phosphorus settling rate in the reach at 20oC [day-1] 1
rk1Carbonaceous biological oxygen demand deoxygenation rate coefficient in the reach at 20oC [day-1] 1
rk2Oxygen reaeration rate in accordance with Fickian diffusion in the reach at 20oC [day-1] 0.0062
rk3Rate of loss of carbonaceous biological oxygen demand due to settling in the reach at 20oC [day-1] 1
bc1 Rate constant for biological oxidation of NH4 to NO2 in the reach at 20oC [day-1] 0.1787
bc2 Rate constant for biological oxidation of NO2 to NO3 in the reach at 20oC [day-1] 0.0076
bc3 Rate constant for hydrolysis of organic N to NH4 in the reach at 20oC [day-1] 0
bc4Rate constant for mineralization of organic P to dissolved P in the reach at 20oC [day-1] 0.0001
4. Routing/in-stream processes in SWAT
14
NO3
NO3
0
1
2
3
4
5
01/01/2002 05/02/2003 11/03/2004 15/04/2005 20/05/2006Time
NO3
(mg/
l)
measured simulated
NO3
0
1
2
3
4
5
0 10 20 30 40 50 60Rank
NO3
(mg/
l)
measured simulated
0
20
40
60
80
100
1/1/02 1/1/03 1/1/04 1/1/05 1/1/06
Time
NO
3 (g
/s)
measuredsimulated
2. CALIBRATION Result of calibration
4. Routing/in-stream processes in SWAT
15
PO4
PO4
0.0
0.1
0.2
0.3
0.4
0.5
01/01/2002 05/02/2003 11/03/2004 15/04/2005 20/05/2006Time
PO4(
mg/
l)
simulated measured
PO4
0
0.1
0.2
0.3
0.4
0.5
0 10 20 30 40 50 60 70Rank
PO4
(mg/
l)
measured simulated
2. CALIBRATION Result of calibration
4. Routing/in-stream processes in SWAT
16
Routing/in-stream processes in SWAT
SWAT with WEST routing
SWAT with SOBEK routing
17
WEST model of a reach of Grote Nete river (calibrated both on flow and water quality)
5. SWAT with WEST routing
18
5. SWAT+WESTIntegrated model SWAT-WEST
in5 + sub5
1
2
3
Input nodes 3 input nodes for diffuse souces which are taken from SWAT
6 input nodes for point souces
5p + sub4
4p + out1+ sub3
WEST river model:
Flow model: 10 tanks in series
Water quality model: simplified RWQM1 with 16 processes and 16 variables
19
Output of SWAT Input of WEST
Directly transfer, only change unit
/COD_OM_S_S
*f_BOD_COD/COD_OM_S_I
*1.5
*1.5
FlowNO3NH3NO2MinPDO
CBOD
CHLA
H2OS_NO3S_NHS_NO2S_POS_O2
S_SS_IX_SX_I
X_HX_N1X_N2X_PXII
X _ALG*α0
From calibration
Integrated model SWAT-WEST
6. SWAT+WEST
20
Routing/in-stream processes in SWAT
SWAT with WEST routing
SWAT with SOBEK routing
21
Integrated model SWAT-SOBEK
Boundary condition
Lateral flow
Cross section
5
4
3
2
5p + sub4
4p+out1+sub3
Input nodes 2 boundary nodes:
+ Upstream: discharge
+ Downstream: water level
8 lateral flow nodes
21 cross sections
SOBEK river model:
Flow model: 1D Saint Venant equation with dx=100m
Water quality model:predefined process “Oxygen and Nutrients”
6. SWAT+SOBEK
22
7. RESULT AND DISCUSSION
23
COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK
Water routingUpstream boundary
Outflow chosen to compare
Downstream boundary
0
4
8
12
16
20
24
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
Flow
(m3/
s)
SOBEKSWATWEST
26
COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEK
NH4
NH4
0
0.5
1
1.5
2
2.5
1/1/200
2
7/1/200
2
1/1/200
3
7/1/200
3
1/1/200
4
7/1/200
4
1/1/200
5
7/1/200
5
1/1/200
6
7/1/200
6
Date
mg/
l
Result fromSOBEK Result from SWAT Result from WEST
SWAT SOBEKNitrification to NO2
Aerobic Growth of heterotrophs
Loss Nitrification
WESTGrowth of 1st stage nitrifier
Gain
Mineralization from orgN
Diffusion from sediment
Respiration of organisms Mineralization from detN
27
COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEKNO3
NO3
0
1
2
3
4
1/1/200
2
7/1/200
2
1/1/200
3
7/1/200
3
1/1/200
4
7/1/200
4
1/1/200
5
7/1/200
5
1/1/200
6
7/1/200
6
Date
mg/
l
Result from SOBEK Result from SWAT Result from WEST
SWAT SOBEK
Aerobic Growth of heterotrophs
Loss Denitrification
WESTAnoxic growth of heterotrophs
Gain
Nitrification to NO3
Diffusion from sediment
Growth of 2nd stage nitrifiers Nitrification of NH4
28
COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEKPO4
PO4
0
0.2
0.4
0.6
1/1/200
2
7/20/2
002
2/5/200
3
8/24/2
003
3/11/2
004
9/27/2
004
4/15/2
005
11/1/
2005
5/20/2
006
12/6/
2006
Date
mg/
l
Result from SOBEK Result from SWATResult from WEST measured value
SWAT SOBEK
Growth of nitrifiers
Loss
Adsorption to inorganic matter
WESTGrowth of heterotrophs
Gain
Mineralization from orgP
Diffusion from sediment
Respiration of organisms Mineralization from detP
29
COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEKCBOD
CBOD
0
2
4
6
8
1/1/2002
7/1/2002
1/1/2003
7/1/2003
1/1/2004
7/1/2004
1/1/2005
7/1/2005
1/1/2006
7/1/2006
Date
mg/
l
Result from SOBEK Result from SWAT Result from WEST
SWAT SOBEK
Loss
WEST
Growth of heterotrophs
Gain
Hydrolysis
Settling to sediment
Decay of OM
Settling to sediment
Decay of OM
30
COMPARISON BETWEEN DIFFERENT SWAT, WEST AND SOBEKDO
DO
0
3
6
9
12
15
1/1/2002
7/1/2002
1/1/2003
7/1/2003
1/1/2004
7/1/2004
1/1/2005
7/1/2005
1/1/2006
7/1/2006
Date
mg/
l
Result from SOBEK Result from SWAT Result from WEST
SWAT SOBEK
Growth of heterotrophs
Loss
WESTGrowth of nitrifiers
Gain Aeration Aeration Aeration
Decay of OM
Nitrification
SOD Respiration of organismsDecay of OM
Nitrification
31
8. CONCLUSION AND RECOMMENDATION
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.
CONCLUSION
32
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