LOGO

Estimating Nitrate Transport in Surface-Subsurface Hydrologic Systems by the linked SWAT-MODFLOW-RT3D Model

Xiaolu WeiRyan Bailey

Rosemary RecordsMazdak Arabi

Tyler Wible

• Model Overview

• Model Linkage

• Applications: Klamath Basin, OR

Outline

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.

RT3D Introduction

Reactive Transport in 3 Dimensions

Dispersion Advection

Sources and Sinks

Reactions

(first-order kinetics)

Model Overview Klamath Basin, ORModel Code

RT3D Introduction

Reactive Transport in 3 Dimensions

• Finite Difference Method

• Same grid as MODFLOW

• Flows/SS from MODFLOW

Model Overview Klamath Basin, ORModel Code

Overview

Model Overview Klamath Basin, ORModel Code

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)

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

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

Simulation Results

Nitrate Concentration in Groundwater

Model Overview Klamath Basin, ORModel Code

High: 1.26 mg/L

Low: 0 mg/L

Simulation Results

Model Overview Klamath Basin, ORModel Code

Groundwater Discharge to Streams

Simulation Results

Model Overview Klamath Basin, ORModel Code

Groundwater Nitrate Loading to Streams

Simulation Results

Model Overview Klamath Basin, ORModel Code

Stream loading comparison

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

Future work

- Keep increasing N leaching from SWAT

- Balance stream flow, stream loading, and leaching

- Applied to Arkansas River Basin

- Developing: ArcGIS interface

AcknowledgementFunding

Acknowledgements

Box Plot for different Land Use

Simulation Results

Model Overview Klamath Basin, ORModel Code

NO

3-N

Co

nce

ntr

atio

n (

mg

/L)

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