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LOGO
Estimating Nitrate Transport in Surface-Subsurface Hydrologic Systems by the linked SWAT-MODFLOW-RT3D Model
Xiaolu WeiRyan Bailey
Rosemary RecordsMazdak Arabi
Tyler Wible
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• Model Overview
• Model Linkage
• Applications: Klamath Basin, OR
Outline
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Overview
Model Overview Klamath Basin, ORModel Code
SWAT
MODFLOW
RT3D
- Groundwater model
- 3D finite difference
- Reactive transport
- 3D finite difference
Method: Link SWAT with physically-based, spatially-distributed groundwater models.
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RT3D Introduction
Reactive Transport in 3 Dimensions
Dispersion Advection
Sources and Sinks
Reactions
(first-order kinetics)
Model Overview Klamath Basin, ORModel Code
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RT3D Introduction
Reactive Transport in 3 Dimensions
• Finite Difference Method
• Same grid as MODFLOW
• Flows/SS from MODFLOW
Model Overview Klamath Basin, ORModel Code
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Overview
Model Overview Klamath Basin, ORModel Code
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SWAT-MODFLOW
Model Overview Klamath Basin, ORModel Code
MODFLOW Grid
Disaggregated HRUs
1. HRU Grid
2. River Cells Subbasin
Recharge
GW Discharge
(Pre-processing tools)
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Soil Percolation
Potential ET not satisfied
River Stage
SWAT
N, P in percolating water
Pumping required
N, P in stream water
MODFLOW
GW/SW Interaction
Water Table Height
Groundwater Flows, Sources/Sinks
RT3D
Mass of N, P to/from Surface Water
N, P concentrations in vadose zone
N, P concentrations in Saturated Zone
Daily Interactions
Linking Three Models
Model Overview Klamath Basin, ORModel Code
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Klamath Basin, Oregon
SWAT Model
MODFLOW ModelUpper Klamath
SWAT Model
- USGS (2012)- 1970-2004- 100,000 grid cells
Records et al (2014)Hydrol. Earth Syst. Sci. 18: 4509–4527
Model Overview Klamath Basin, ORModel Code
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Simulation Results
Nitrate Concentration in Groundwater
Model Overview Klamath Basin, ORModel Code
High: 1.26 mg/L
Low: 0 mg/L
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Simulation Results
Model Overview Klamath Basin, ORModel Code
Groundwater Discharge to Streams
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Simulation Results
Model Overview Klamath Basin, ORModel Code
Groundwater Nitrate Loading to Streams
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Simulation Results
Model Overview Klamath Basin, ORModel Code
Stream loading comparison
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Simulation Results
Model Overview Klamath Basin, ORModel Code
Frequency Plot
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 More
Freq
uen
cy
NO3-N Concentration (mg/L)
Observed Data
Simulated _ Surrounding Wells
Simulated _ Entire Basin
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 More
Freq
uen
cy
NO3-N Concentration (mg/L)
Observed Data
Simulated _ Surrounding Wells
Simulated _ Entire Basin
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Future work
- Keep increasing N leaching from SWAT
- Balance stream flow, stream loading, and leaching
- Applied to Arkansas River Basin
- Developing: ArcGIS interface
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AcknowledgementFunding
Acknowledgements
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Box Plot for different Land Use
Simulation Results
Model Overview Klamath Basin, ORModel Code
NO
3-N
Co
nce
ntr
atio
n (
mg
/L)
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Code Structure
Model Overview Klamath Basin, ORModel Code
simulate
Read/Allocate arrays MODFLOW / RT3D
Years
Days
command
1: subbasin (hru calculations)
19: MODFLOW / RT3D
HRU values disaggregated HRUs (DHRUs)
DHRUs Grid cells
River stage MODFLOW River cells
Run MODFLOWRun RT3D
Map SWAT Grid
Map Grid SWATGW Discharge Subbasin streams
NO3 loading Subbasin streams
2: Route
NO3 in percolation
NO3 in river water
Denitrification
Surface
Aquifer
Routine