IN-STREAM WATER QUALITY PROCESSES IN SWAT · 2 CATCHMENT MODELLING RIVER WATER QUALITY MODELLING...

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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

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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

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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

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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

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3. STUDY AREA: Grote Nete basin

Pollution sources

Agriculture Households

WWTPs

Industry

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SWAT model of Grote Nete river basin (calibrated on flow, water quality: not calibrated)

+ 14 subbasins (1 point source/subbasin)

+ 71 HRU


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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


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Routing/in-stream processes in SWAT

SWAT with WEST routing

SWAT with SOBEK routing

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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)

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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

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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


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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.


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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


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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


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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


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WEST model of a reach of Grote Nete river (calibrated both on flow and water quality)

5. SWAT with WEST routing

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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

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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

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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

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7. RESULT AND DISCUSSION

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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

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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

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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


Growth of 2nd stage nitrifiers Nitrification of NH4

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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


Respiration of organisms Mineralization from detP

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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


SWAT SOBEK

Loss

WEST

Growth of heterotrophs

Gain

Hydrolysis

Settling to sediment

Decay of OM

Settling to sediment

Decay of OM

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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


SWAT SOBEK

Growth of heterotrophs

Loss

WESTGrowth of nitrifiers

Gain Aeration Aeration Aeration

Decay of OM

Nitrification

SOD Respiration of organismsDecay of OM

Nitrification

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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

IN-STREAM WATER QUALITY PROCESSES IN SWAT · 2 CATCHMENT MODELLING RIVER WATER QUALITY MODELLING...

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