A Model for Evaluating the Impacts of Spatial and Temporal Land Use Changes

on Water Quality at Watershed Scale

Jae-Pil Cho and Saied Mostaghimi

07/29/2003

Overview of presentation

Introduction Model characteristics Model components Model application Summary & Future improvement

Introduction

Effectiveness of BMPs varies both temporally and spatially

Ideal NPS model for BMP evaluation Long-term, continuous-simulation model Distributed-parameter model Process-oriented model

Objectives To develop a continuous, distributed, and

process-oriented watershed scale model for assessing the effectiveness of temporally and spatially changing BMPs

To demonstrate the model applicability

Model Characteristics

Conceptual Model

Baseflow

Interflow

Root zone

Interception Evapotranspiration

Infiltration

Percolation

Overland flow

Channel flow

Flowchart of the model

Define soil layers

Read main input

Begin Simulation

Initialize the model

End SimulationSimulation Period Over ?

Read weather data (1day)

Yes

Pesticide degradation

Calculate daily changing

Check rotation changes

Calculate daily changing variables (ET,crop, soil,surface)

No

Runoff=0 ?No

Read breakpoint data(get start time of rainfall)

Yes

Overland flow routing

Infiltration

Overland sediment routing

Overland pesticide routing

Channel flow routing

Percolation

Pesticide leaching

Channel sediment routing

Channel Pesticide routing

Lumped Interflow and Baseflow

Precipitation ? No

Yes

Multiple soil layers based on physical soil layers and rotation information such as pesticide application depth and tillage depth

Soil Parameters• Porosity, bulk density• Effective hydraulic conductivity• Rill and Interrill erodibilityCrop Parameters• Canopy cover and height• Leaf Area Index(LAI)• Root depthGround surface parameters• Random roughness• Ridge height• Residues(flat, buried, dead root)

RunoffRunoff

RainfallRainfall

1-dayUser defined during rainfall time step

Before rainfall

time step

During rainfall

time step

After runoff

time step

Separate input files

Blocks in main inputSeparate output files

Output parametersOutput parameters

WeatherWeather

Break-pointBreak-point

MainMain

InitialInitial

Flag & General inputFlag & General input

InitialInitial

CellCell

CropCrop

TillageTillage

PesticidePesticide

RotationRotation

ChannelChannel

SoilSoil

OutputRotation InitialRotation Initial

Input file structure for considering spatial and temporal land use changes

Physical Data

Temporal Data

Spatial Data

Dynamic parameters

Leaf Area Index (LAI) Canopy cover Canopy height Root depth

CropCrop

SurfaceSurface

SoilSoil

Water andTemperatur

e stress

Biomass Above ground Root Random roughness

Ridge height Residues

Flat residue Buried residue Dead root residue

Porosity, B-Density Effective hydraulic conductivity Rill and Interrill

erodibility

Rainfall Cu. amount Kinematic E.

Spatial and Temporal Land Use Changes

Tillage Type App. date

Model Components

Hydrology & Sediment

Hydrology Overland flow: Continuity and Manning’s

equation Evapotranspiration: Ritchie’s method Infiltration: Green-Ampt infiltration for

unsteady rainfall Percolation: WEPP approach

Sediment (Based on WEPP) Rill detachment Interrill detachment Channel scour

Pesticide: application methods

Surface and Foliage application User defined depth & linearly decreasing with depth

Soil and foliage

application

Depth Pesticide

Incorporation

Pesticide

Injection

Pesticide

Incorporation User defined depth & Uniform distribution

Injection User defined depth & no mixing above this depth

Pesticide:Retention / degradation / transport

Interaction between solution and soil phase Linear isotherm: instantaneous & reversible

Cs = Kd X Cw

Degradation First-order kinetics: lumped dissipation

parameter

Cd = Co e –k d Adjustment of dissipation rate based on soil

temperature and soil moisture content Transport

Runoff Leaching Plant uptake

Model Application

Nomini Creek Watershed

Virginia

WestmorelandCounty

$

$

##

# #

#

##

#

%

%

%

%

%

%

%

PN1

PN2

PN3

PN4

PN5

PN6

PN7GN1GN2

GN3

GN4

GN5GN7GN8

GN6

QN1

QN2

QN1 boundaryQN2 boundaryStream

$ Stream gaging stations# Ground water wells% Precipitation gages

1 0 1 2 Miles

N

EW

S

Nomini Creek Watershed

Ground water dominant watershed(GWI=0.85)

Detail land use changes and pesticide application data (1985-1997) Typical planting, harvesting, tillage, pesticide

application date was decided Simulation period: 01/01/1989- 12/31/1991 Cell size: 90m*90m (267 cells) Pesticide

Pesticide

Solubility

(ppm)

Half Life Soil(days

)

Half Life

Foliage

Washoff

Fraction

Koc(ml/g)

Atrazine

33.0 60 5 0.5 100

Land use changes in QN2 55 fields and 36 different land use changes Land use changes in field#6 (1989-1991)

Pesticide application

Pesticide application

Corn

Small grain

Soybean

Corn

Tillage application

Available Output Files

Flux Surface to Root zone Root to Intermediate zone

Outlet Daily Event

User defined cell Vertical distribution Time series Dynamic soil, crop, surface parameters

Outlet output: Daily and monthly runoff

02468

1012141618

1/1/1989 1/1/1990 1/1/1991

Date

Dai

ly R

unof

f (m

m) Observed (mm) Simulated (mm)

0

10

20

30

40

50

60

70

80

Jan-

89

Apr-8

9

Jul-8

9

Oct-89

Jan-

90

Apr-9

0

Jul-9

0

Oct-90

Jan-

91

Apr-9

1

Jul-9

1

Oct-91

Month

Mon

thly

Run

off

(mm

) ObservedSimulated

Error QN2(89’-91’)

Error in total volume -11.56 %

0.0

0.1

0.2

0.3

0.4

0.5

1/1/89 1/31/89 3/2/89 4/1/89 5/1/89 5/31/89 6/30/89 7/30/89 8/29/89 9/28/89 10/28/89 11/27/89 12/27/89

Da

ily P

est

icid

e L

oss

(mg)

0.0

0.5

1.0

1.5

2.0

Jan-89 Feb-89 Mar-89 Apr-89 May-89 Jun-89 Jul-89 Aug-89 Sep-89 Oct-89 Nov-89 Dec-89

Mo

nth

ly P

est

icid

e L

oss

(mg

)

Outlet output: Daily and monthly pesticide load

Daily

Monthly

0

0.2

0.4

0.6

0.8

1

0 500 1000 1500

Time (minutes)

Flo

w R

ate

(m

3/se

c)

Outlet output: Event hydrograph

0.000

0.001

0.002

0.003

0.004

0.005

0 500 1000 1500

Time (minutes)

Con

cent

ratio

n (u

g/l)

07/16/89 Storm event

User-defined cell output:- Vertical distribution of pesticide concentration

0.00.20.40.60.81.01.21.41.6

0 5000 10000 15000

Concentration (ug/l)D

ep

th (

m)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 500 1000

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 200 400 600

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 20 40 60

Concentration (ug/l)

Dep

th (m

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 10 20 30

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 5 10 15

4/26/1989(Application)

5/5/1989

8/5/1989 9/5/1989 10/5/1989

6/5/1989

Conclusions & Future Improvement A model was developed for assessing

the impacts of spatial and temporal land use changes on hydrology and water quality and applied to NC watershed

Future improvement Model validation (Hydrology, sediment,

pesticide) Distributed ground water modeling

Linkage with MODFLOW and MT3DMS Pre- and post-processor

Expecting modeling system

GIS

WeatherData

Surface/Unsaturated zone model

Surface/Unsaturated zone model

MODFLOW/MT3DMSMODFLOW/MT3DMS

ResultDBOutputInput

InputDB

Arc/View(ASCII)

Pesticide,Crop, SoilData

OutputInput

-Weather-Rainfall Input

Excel(VBA)

1

2

3 4

Interface

Data flow

1

2

Update input database

Create weather and breakpoint rainfall input data

3Create main input

4 Update result database

Interface

THANK YOU…

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