Modeling Agrichemical Transport in Midwest Rivers Using Geographic
Information Systems
By Pawel J. Mizgalewicz and David R. Maidment
ABSTRACT
A method is proposed for regionalizing watershed scale water quality
estimates. Elementary watersheds are delineated using digital elevation
data and linked to form a river basin scale watershed network. Elementary
watersheds are combined into stream gauge zones for which the only
streamflows into and out of a zone are those measured at the zone
boundary by stream gauges. Time series of monthly streamflow are
obtained by an interpolation procedure in which monthly precipitation
over each elementary watershed is converted to streamflow by a runoff
coefficient, and then adjusted so that the accumulated streamflow
over the gauge zone is equal to the measured outflow. Concentrations
of water quality constituents are found from regression equations
in which the mean annual concentration is estimated as a function
of watershed, chemical application and climatic characteristics,
and a ratio of expected monthly to annual concentration is applied.
Parameters of these equations were found for two constituents: nitrate
plus nitrite as nitrogen, and atrazine, using data sampled by the
US Geological Survey at 151 sites in the Missouri, Upper Mississippi
and Ohio River basins. Nitrate plus nitrite concentrations show
a fairly uniform seasonal pattern and some dependence on spatial
factors; atrazine concentrations show a strong seasonal pattern
with high values in May and June, and little dependence on spatial
factors. Both constituents appear to increase in concentration with
discharge to the 0.3 power approximately. An example application
of the method is made to the 32,000 km2 Iowa-Cedar River
basin using elementary watersheds of average area approximately
30 km2 . In this basin, constituent loading estimates
determined using discharge-dependent concentrations appear to be
too large when compared with independent loading estimates, which
suggests that the sampled water quality database may be somewhat
biased towards processes occurring during high runoff rather than
baseflow periods. Loading estimates found from discharge-independent
concentrations are more reasonable.
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View the Whole Report... 8,774kb
TABLE OF CONTENTS
Title Pages
... 7 kb
Abstract...
8 kb
TABLE OF CONTENTS
... 105 kb
LIST OF TABLES
LIST OF FIGURES
LIST OF PROCEDURES
1. INTRODUCTION
... 23kb1.1 MOTIVATION
1.2 OBJECTIVES
1.3 SCOPE OF STUDY
1.4 PROJECT SUMMARY
1.5 CONTRIBUTIONS OF STUDY
2. LITERATURE
REVIEW ... 46 kb
2.1 LINKING GIS WITH WATER QUALITY MODELS
2.2 GIS MODELS OF WATER QUALITY
2.3 GIS AS A TOOL FOR SPATIAL DATA EXTRACTION
2.4 COMPARISON OF THE PROPOSED METHOD WITH PREVIOUS STUDIES
2.4.1 Time domain
2.4.2 Spatial domain
2.4.3 Model formulation
3. DATA AND COMPUTER
SOFTWARE DESCRIPTION ... 2,399 kb
3.1 DATA SOURCES
3.1.1 Herbicide and nutrient data
3.1.2 Digital Terrain Representation
3.1.3 Reach File 1
3.1.4 Atrazine and nitrogen fertilizer use
3.1.5 Hydrologic and climatic data
3.1.6 Maps of mean annual precipitation and temperature
3.2 COMPUTER SOFTWARE DESCRIPTION
3.2.1 GIS software
3.2.2 Statistical software
4. METHODOLOGY
... 3,504 kb
4.1 REPRESENTATIVE AGRICULTURAL CHEMICALS
4.1.1 Nitrate
4.1.2 Atrazine
4.2 SELECTION OF ANALYSIS REGION AND MAP COORDINATE SYSTEM
4.3 MATHEMATICAL DESCRIPTION
4.3.1 Overview of transport equations
4.3.2 GIS and cascade modeling.
4.3.3 Regression equation development
4.3.4 Agrichemical runoff from the field
4.3.5 Transport in rivers
4.3.6 Seasonal variations
4.3.7 Extracting values of explanatory variables for the regression
analysis
4.3.8 Application of the regression models
4.4 GIS MODEL DESCRIPTION 4.4.1 Subdivision of study region into
modeling units
4.4.2 Unit watershed flow system
4.4.3 Ordering system of the modeling units
4.4.4 Enhancement of the stream delineation process
4.5 REDISTRIBUTION OF THE FLOW RECORD OVER UNGAUGED RIVERS
4.5.1 GIS database of monthly flow rate and the precipitation depth
4.5.2 Average precipitation depth in modeling units
4.5.3 Mathematical description
4.5.4 Example of flow redistribution.
4.6 EXPONENTIAL DECAY MODEL 4.6.1 Exponential decay model overview
4.6.2 Travel time approximation
5. PROCEDURES
... 1,332 kb
5.1 CONCENTRATION AND FLOW MEASUREMENTS
5.2 PREPARING DATA FOR MODEL PARAMETER ESTIMATION
5.2.1 Preparing 500 m (15'') DEM for analysis
5.2.2 Estimation of watershed parameters
5.2.3 Creating grid of sampling sites
5.2.4 Adjusting location of sampling sites
5.2.5 Extracting parameters of the sampled site watersheds
5.2.6 Agrichemical application
5.2.7 Annual temperature and annual precipitation depth
5.3 PREPARING DATA FOR STATISTICAL ANALYSIS
5.4 AGRICHEMICAL CONCENTRATIONS IN THE IOWA-CEDAR RIVER BASIN
5.4.1 Creating a map of the flow direction.
5.4.2 Map of the modeling unit outlets
5.4.3 Watershed connectivity
5.4.4 Refining modeling units
5.4.5 Database of monthly precipitation depth and monthly flow rate
5.4.6 Average precipitation depth in modeling units
5.4.7 Spatial distribution of flow
5.4.8 Determining input values for the Iowa-Cedar River model
5.5 ARCVIEW MODEL OF AGRICHEMICAL TRANSPORT
5.5.1 Model overview
5.5.2 Project “Model”
5.5.3 Project “Results”
5.5.4 Project “Flwprc”
5.5.5 Project “Tools”
6. RESULTS
... 1,095 kb
6.1 SEASONAL VARIATION OF AGRICHEMICALS IN THE MIDWEST STREAMS 6.1.1
Seasonal variation of the atrazine concentration
6.1.2 Seasonal variation of the nitrate plus nitrite as nitrogen
concentration
6.2 AVERAGE ANNUAL AGRICHEMICAL CONCENTRATION IN THE MIDWEST STREAMS
6.2.1 Average annual atrazine concentration in the Midwest rivers
6.2.2 Average annual nitrate plus nitrite as nitrogen concentration
6.3 ERROR OF MODEL PREDICTIONS
6.4 COMPARISON OF PREDICTED FLOW WITH OBSERVED ONE
6.5 AGRICHEMICAL CONCENTRATIONS IN THE CEDAR RIVER BASIN
7. SUMMARY, CONCLUSIONS,
AND RECOMMENDATIONS ... 28 kb
APPENDICES
... 208 kb
APPENDIX A C-CODES
A1 Program newnx.c--reconstructing the flow connectivity between
modeling units after some of units have been removed
A2 Program fdy4.c--calculating the flow rate in ungauged streams
from the available record
APPENDIX B AVENUE SCRIPTS
B1 Changing ArcView projects from the PushButton Bar.
B2 Scripts from the project “model”
B3 Scripts from the project “results”
B4 Scripts from the project “flwprc”
B5 Scripts from the project “tools”
APPENDIX C ARC/INFO MACROS--AMLS
C1 WSHGS.AML
C2 NEXTWSH.AML
C3 RAININFO.AML
C4 RAINMAP.AML
C5 RAINM2.AML
C6 SELDATA.AML
C7 FD4Y.AML
C8 SLOPE3.AML
C9 DEMALB.AML
BIBLIOGRAPHY
... 53kb
These materials may be used for study, research, and education,
but please credit the authors and the Center for Research in Water
Resources, The University of Texas at Austin. All commercial rights
reserved. Copyright 1997 Center for Research in Water Resources.
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