1. General Model Information
Name: Groundwater Loading Effects of Agricultural Management Systems
Main medium: terrestrial
Main subject: biogeochemistry, hydrology
Organization level: ecosystem
Type of model: ordinary differential equations, partial differential equations
Main application: research
Keywords: chemical movement, root zone, agricultural management effects
Frank M. Davis
Southeast Watershed Research Laboratory (SEWRL)
South Atlantic Area
P. O. Box 946
Tifton, GA 31793
Phone: (229) 391-6846
R.A. Leonard; F.M. Davis; W.G. Knisel.
Groundwater Loading Effects of Agricultural Management Systems
(GLEAMS) is a continuous simulation, field scale model, which
was developed as an extension of the Chemicals, Runoff and
Erosion from Agricultural Management Systems (CREAMS) model.
GLEAMS assumes that a field has homogeneous land use, soils,
and precipitation. It consists of four major components:
hydrology , erosion/sediment yield, pesticide transport, and
nutrients. GLEAMS was developed to evaluate the impact of
management practices on potential pesticide and nutrient
leaching within, through, and below the root zone. It also
estimates surface runoff and sediment losses from the field.
GLEAMS was not developed as an absolute predictor of pollutant
loading. It is a tool for comparative analysis of complex
pesticide chemistry, soil properties, and climate. GLEAMS can
be used to assess the effect of farm level management decisions
on water quality.
Water Quality Applications
GLEAMS can provide estimates of the impact management systems,
such as planting dates, croppina systems, irrigation scheduling,
and tillage operations, have on the potential for chemical
movement. Application rates, methods, and timing can be altered
to account for these systems and to reduce the possibility of
root zone leaching. The model also accounts for varying soils
and weather in determining leaching potential. GLEAMS can also
be useful in long-term simulations for pesticide screening of
soil/management. The model tracks movement of pesticides with
percolated water, runoff, and sediment. Upward movement of
pesticides and plant uptake are simulated with evaporation and
transpiration. Degradation into metabolites is also simulated
for compounds that have potentially toxic products. Erosion in
overland flow areas is estimated using a modified Universal
Soil Loss Equation. Erosion in chemicals and deposition in
temporary impoundments such as tile outlet terraces are used to
determine sediment yield at the edge of the field.
Source: USDA-ARS, Natural Resources Systems Research Unit:
- Automatic irrigation, manual irrigation, and chemigation options
- The erosion/sediment yield component is very comprehensive,
which allows the user to describe in detail the topgraphic
features of the field.
- All channels in the field are assumed to be naturally eroded.
- The evapotranspiration and canopy interception modules allow
simulation of management alternatives in forested areas.
current version (Sep 2000): 3.0
Programming Language(s): FORTRAN 77 (see Section II.1)
User Manual (pdf file): SEWRL, Models, Gleams: http://sacs.cpes.peachnet.edu/sewrl/
Quantity of Available: required includes daily rainfall and temperature, however,rainfall data can be skewed by results of one storm.Other Shortfalls: Default values and data tables are available, but these do not prohibitmodel execution, only reduce the quality of results. Operator error is the only thing that prohibitsmodel execution. Model results cannot be any better than the data input.
III. Mathematical Information
see User Manual ( II.3 )
Model Input Data Requirements: Daily rainfall and temperature; monthly temperature, solar radiation, wind movement, and dewpoint temperature; soil characteristics; pesticide characteristics and application data; fertilization and tillage data.
Model Input Data Source: Various--climatological data; soils data publications; pesticide data bases; erosion handbooks; friends.
Model Output Data: Various--daily, monthly, annual. Runoff, sediment, pesticide mass and concentration, percolation volume, plant nutrient mass and concentrations.
Temporal Scale: Daily
Spatial Scale: Field-size areas
see further publications and abstracts at: http://sacs.cpes.peachnet.edu/sewrl/Gleams/glmspub.htm
Knisel, W.G., R.A. Leonard, and F.M. Davis.GLEAMS Version 2.1 Part I:Model Documentation. UGA-CPES-BAED, Pub. 5, Nov. 1993.
Leonard, R.A., W.G. Knisel, and D.A. Still. 1987.GLEAMS: Groundwater LoadingEffects of Agricultural Management Systems. Trans. Amer. Soc. of Agric. Engrs.30: 1403-1418.
Knisel, W.G.,F.M.Davis, and R.A.Leornard.1994GLEAMS VERSION 2.0PartIII:User Manual.USDA-ARS,Coastel Plain Experiment Station.Southeast Watershed Research Laboratory.Tifton, Georgia, 31793.200pp.
Knisel,W.G.,R.A.Leornard,and F.M.Davis.1994The GLEAMS MODEL PLANT NUTRIENT COMPONENTPart I:MODEL DOCUMENTATION.USDA.ARS,Coastal Plain Experiment Station.Southeast WatershedResearch Laboratory.Tifton,Georgia,31793.57pp.
Knisel,W.G.(Editor).1980.CREAMS:A field-scale model for Chemical,Runoff,and Erosionfrom Agricultural Management Systems.US Department of Agriculture,Science and Education Administration,Conservation,Report No.26.643pp.
V. Further information in the World-Wide-Web
VI. Additional remarks
This model of agricultural management practices of farm chemical flows can be used to examine the human factors contributing to global environmentalchange. The model has the capacity to study long term effects of pesticide management practices.
Last review of this document by: J. Bierwirth: 20. 10. 2000
Status of the document:
last modified by
Tobias Gabele Wed Aug 21 21:44:44 CEST 2002