PUBLICATIONS

Knisel, W. G. (Ed.). 1980. CREAMS: A field-scale model for non-point source pollution evaluation. Proc. Non-point Pollution Control Tools and Techniques for the Future Symposium. Gettysburg, PA. June 11-13. pp. 100-106.

ABSTRACT: The publication describes a mathematical model developed to evaluate non-point source pollution from field-sized areas. CREAMS consists of three components: hydrology, erosion/sedimentation, and chemistry. The publications is presented in three volumes: Volume I, model documentation, describes the concepts of each of the model components; Volume II, user manual, describes the model application and selection of parameter values; Volume III, supporting documentation, provides additional data and parameter information.

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Svetlosanov, V., and W. G. Knisel (eds.) 1982. European and U. S. Case Studies in Application of the CREAMS Model. International Institute for Applied Systems Analysis, Laxenburg, Austria. CP-82-S11. 148 pp.

ABSTRACT: A brief description is given for all components of the CREAMS model. Applications of CREAMS in European countries and the United States are presented as case studies. Case studies in Finland, Federal Republic of Germany (West Germany), Poland, Sweden, England, U.S.S.R., Czechoslovakia, and the U.S.A. are presented to demonstrate applications of the model for evaluating alternate management practices. A review and discussion of the case studies are given.


Leonard, R. A., W. G. Knisel, D. A. Still, and A. W. Johnson. 1985. Modeling vertical flux of pesticides with CREAMS. Proc., Nonpoint Source Pollution Abatement Symposium. Milwaukee, Wisconsin, Apr. 23-25. pp. T-I-D-1 to T-I-D-12.

ABSTRACT: The pesticide component of the CREAMS model considered only surface runoff and sediment losses of pesticides, and any movement of pesticides below the surface 1-cm of soil was "lost" from the active evaluations. The hydrology, erosion, and pesticide components of CREAMS were modified for assessing the vertical flux of pesticides into and through the effective root zone of the soil. The principles of pesticide movement through the soil computational layers are described in the paper, and these modifications became the basis for development of the GLEAMS model.


Leonard, R. A., W. G. Knisel, and D. A. Still. 1987. GLEAMS: Groundwater Loading Effects of Agricultural Management Systems. Trans., Amer. Soc. of Agric. Engrs. 30:1403-1418.

ABSTRACT: GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) is a mathematical model developed for field-size areas to evaluate the effects of agricultural management systems on the movement of agricultural chemicals within and through the plant root zone. This paper describes the concepts of the hydrology, erosion, and pesticide components of GLEAMS. Results of sensitivity analysis and validation with observed bromide and pesticide data are given. The validation includes comparisons of model simulations and observed soil concentrations in the root zone, and simulated and observed leaching losses.

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Leonard, R. A., and W. G. Knisel. 1988. Evaluating groundwater contamination potential from herbicide use. Weed Tech. 2:207-216.

ABSTRACT: Potential herbicide loadings to groundwater are determined by soil, chemical, management, and climatic factors. Several simple assessment procedures to rank pesticides according to their potential impact on groundwater are available. Most of these procedures are not specific to any climatic region, cropping practice, or soil. Using a continuous simulation model, GLEAMS, to assess potential herbicide leaching allows more condition-specific assessment. Simple relationships for relative comparisons in a specific soil/climate setting were developed by relating simulated 50-yr mean leaching losses to the herbicide half-life/Koc ratio. Other criteria of herbicide leaching potential such as 50-yr maxima or other values based on probability distributions could be used. Although differences in soils were demonstrated in this exercise, the same procedures could be applied to different management systems.


Asmussen, L. E., D. W. Hicks, R. A. Leonard, W. G. Knisel, and H. F. Perkins. 1989. Potential pesticide contamination in ground-water recharge areas: A model simulation. Proc., Georgia Water Res. Conf., Athens, Georgia, May 15-16. pp. 161-164.

ABSTRACT: Results of 50-year GLEAMS model simulations indicate soil characteristics and agricultural management have a profound affect on the quality of ground water loadings in aquifer recharge areas. Thus it is important to develop a system for assessing the long-term impacts of agricultural management on groundwater quality. Field-scale model simulations for different surface and subsurface soil strata can indicate where chemicals may be transmitted to aquifer systems and where underlying layers may prevent aquifer contamination.


Beasley, D.B., W. G. Knisel, and A. P. Rice (Eds.) Proceedings of the CREAMS/GLEAMS Symposium, Athens, Georgia, September 27-29. UGA-CPES-Agricultural Engineering Department, Tifton, Georgia, Publication No. 4. 247 pp.

ABSTRACT: Concepts, philosophies, and overviews of modeling are given with emphasis on CREAMS and GLEAMS models. Modifications and applications of CREAMS and GLEAMS given by research scientists and specialists in universities, federal and state agencies, and agrichemical industries. Papers are presented for applications in Canada and Italy as well as the U.S.


Knisel, W. G., and R. A. Leonard. 1989. Irrigation impact on groundwater: A model study in the humid region. Amer. Soc. of Civil Engrs., J. of Irr. & Drain. Engr., 115(5):791-806.

ABSTRACT: The Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) model was applied to estimate the effects of: (1) soil; (2) planting date; (3) irrigation level; and (4) pesticide characteristic on pesticide leaching below the root zone of representative coarse-grained soils. Climate/application/pesticide characteristic interactions are shown to significantly affect pesticide losses, whereas irrigation practice has little effect. Persistent and mobile compounds exhibit the highest losses.


Knisel, W. G., R. A. Leonard, and F. M. Davis. 1989. Agricultural management alternatives: GLEAMS model simulations. Proc., Computer Simulation Conf., Austin, Texas, July 24-27. pp. 701-706.

ABSTRACT: The GLEAMS model was used to simulate potential pesticide loadings to groundwater for alternative management strategies. A 50-year climatic record at Tifton, Georgia was used to estimate impacts of alternate planting dates, irrigation scheduling and depths applied, and pesticide selection and application dates on loot zone leaching for two representative Coastal Plain soils. Results of simulation are given to demonstrate the utility of comprehensive model applications to select among possible alternative systems to maintain or improve groundwater quality.


Leonard, R. A., and W. G. Knisel. 1989. Groundwater loadings by controlled-release pesticides: A GLEAMS simulation. Trans., Amer. Soc. of Agric. Engrs., 32(6):1915-1922.

ABSTRACT: Controlled-release pesticide application was represented for the GLEAMS model simulation to evaluate impacts of the practice on leaching below the root zone. Pesticides with high mobility and slight to moderate persistence were simulated using a 50-year climatic record at Tifton, Georgia on two representative soils that occur in groundwater recharge areas of the Coastal Plain. A threshold level of pesticide concentration in the soil surface 7.5 cm was assumed for targeted pest control, and the annual duration of time the threshold was exceeded was analyzed for each simulated formulation. This measure of control and simulated leaching through the bottom of the root zone were analyzed to consider efficacy as well as potential impact on groundwater loadings.


Leonard, R. A., W. G. Knisel, and F. M. Davis. 1989. Groundwater loadings of pesticides from chemigation: A GLEAMS model simulation. Proc., Amer. Soc. of Civil Engrs., Irr. & Drain. Natl. Water Conf., Newark, Delaware, July 17-20. pp. 430-442.

ABSTRACT: The GLEAMS model has been shown to be an effective tool in assessing potential pesticide leaching below the root zone. A wide range of management scenarios can be represented effectively with the model. A modification was made to consider the effects of a common practice in intensely-managed irrigation areas: chemigation.

Chemical application in irrigation systems is an efficient method of pesticide application even when crop height is too great for ground rig operation. Also this method permits timely applications when soil or weather conditions are not conducive to other methods. However, the environmental impact, particularly on groundwater quality, has been questioned.

Little data have been obtained on pesticide leaching under chemigation systems. There has been considerable speculation by proponents and opponents of the method without conclusive evidence the or against. The limited data available cannot be transferred to other climate, soil, and aquifer conditions without the use of models.

This paper describes how, with slight modifications, the GLEAMS model was used to represent chemigation for herbicides, nematicides, insecticides, and fungicides applied through overhead sprinkler systems. Simulation results were compared with limited data available on soil pesticide concentrations subsequent to applications by chemigation. A 50-year climatic record at the Coastal Plain Experiment Station near Tifton, Georgia (USA) was used to demonstrate the application on two representative Coastal Plain soils. Results of the simulations are presented in the paper, and leaching losses are compared for conventional and chemigation application of pesticides.


Leonard, R. A., H. F. Perkins, and W. G. Knisel. 1989. Relating agrichemical runoff and leaching to soil taxonomy. Proc., Georgia Water Res. Conf., Athens, Georgia, May 15-16. pp. 158-160.

ABSTRACT: Complex interactions of agrichemical properties and processes, farm management practices, climatic factors, and soils result in an infinite number of possible combinations requiring decisions by management and regulatory agencies to alleviate water quality problems. Mathematical models representing these interactions provide the only feasible means of making sound decisions. Short-term data collection must be supplemented with model applications to extrapolate results to other climates, soils, management systems. A method of combining (grouping) soils and pesticide characteristics is presented in this paper with application of the GLEAMS model to demonstrate the methodology. Pesticide persistence and mobility characteristics are arranged in groups, or classes, and some Coastal Plain soils are grouped by taxonomy that reflect their capability to produce runoff and transmit water into and within the profile. These combinatorial factors are treated in the model application to show the applicability of the method.


Magliola, C., and W. G. Knisel. 1989. Impact of agriculture on water quality in Circeo National Park, Italy: A model study. I--Pesticides. In: D. B. Beasley, W. G. Knisel, and A. P. Rice (Eds.) Proceedings of the CREAMS/GLEAMS Symposium, Athens, Georgia, September 27-29. UGA-CPES-Agricultural Engineering Department, Tifton, Georgia, Publication No. 4. pp. 161-169.

ABSTRACT: The GLEAMS model was applied for representative agricultural systems of the Circeo National Park area, Italy, to estimate the potential for pesticide inflow by surface waters and shallow groundwater into the Park lakes. Two cropping systems were modeled on the two major agricultural soils using climatic data for 1986-87. Selected pesticides were represented in the model applications, and similar analyses were made for a range of pesticide characteristics. Results of the model studies showed that surface runoff losses of pesticides were negligible for all characteristics on both soils. Potential pesticide leaching was simulated for most compounds represented on the sandy, low organic matter soil. However, leaching was simulated for only the very mobile pesticides with long half-life on the soil with a high organic subsoil.


Shirmohammadi, A., and W. G. Knisel. 1989. Irrigated agriculture and water quality in the South. Amer. Soc. of Civil Engrs., J. of Irr. & Drain. Engr., 115(5):823-838.

ABSTRACT: Irrigated agriculture in the humid region has resulted in more intensive management including crop production and the associated increase in fertilizer and pesticide use. Multiple cropping in most of the southeast (Alabama, Florida, Georgia, and South Carolina) and Delta states (Arkansas, Louisiana, and Mississippi) increases the demand for water and agricultural chemicals. Pesticide usage in the 48 contiguous states and the District of Columbia totaled 299,829,159 kg of active ingredient (AI) by 1982. Agricultural chemicals may percolate to aquifers in some soils and geologic formations resulting in groundwater contamination. Groundwater fluctuations are related to irrigation. Groundwater quality data are used to show the trend in quality related to irrigated agriculture and cropping systems. Areas with specific groundwater problems such as salt-water intrusion and pesticide levels are identified. A total of 17 pesticides have been reported in groundwater in the U.S. and four of these were found in the southeast and Delta states. Data show that less than 1% of wells in these states had nitrate concentrations exceeding the 10 mg/L drinking water standard. Degradation of surface water quality relative to irrigation is discussed in the paper.


Knisel, W. G., and R. A. Leonard. 1990. Representative climatic record for pesticide runoff and leaching simulations. Dept. Pub. No. 2, Agric. Engr. Dept., Univ. of Georgia, Coastal Plain Expt. Sta., Tifton. 16 pp.

ABSTRACT: Rainfall amount and distribution for year-to-year and within the year are important in selecting a representative climatic record for model simulation of pesticide runoff and leaching. Long-term simulations are necessary for risk analyses and to experience the chance occurrence of runoff-producing storms. A 50-year climatic record in the Coastal Plain of Georgia was used with the GLEAMS model to consider the effects of year-to-year differences in annual and seasonal amounts of rainfall on runoff, percolation, and the annual runoff and leaching losses of mobile pesticides. Moving average schemes for 3- and 5-year periods were used to compare long-term and short-term simulated values for different time periods.


Leonard, R. A., and W. G. Knisel. 1990. Can pesticide transport models be validated with field data: Now and in the future? Dept. Pub. No. 3, Agric. Engr. Dept., Univ. of Georgia, Coastal Plain Expt. Sta., Tifton. 26 pp.

ABSTRACT: Pesticide runoff models developed in the 1980's have proven useful in evaluating management practices and in pesticide registration. As computer systems become more powerful and water quality concerns extend to groundwater as well as surface water, conceptually sound and adequately validated models must provide the foundation of further model development.

Theory of pesticide entrainment in runoff and leachate and representation in models is reviewed in the paper. Limitations in calibration and validation using field data are discussed relative to data deficiencies and uncertainties, parameter variabilities, and different degrees of temporal and spatial resolution in hydrology, sediment transport, and chemistry data. Comparisons of results from model simulations with field data on pesticide runoff, leaching, and/or persistence in the root zone are valuable and may provide general confirmation that a model provides a "reasonable" representation of the real world. The uncontrolled nature of field data is discussed as well as how developers tend to add more sophistication that cannot be evaluated using field data.


Leonard, R. A., W. G. Knisel, F. M. Davis. 1990. The GLEAMS model - A tool for evaluating Agrichemical ground-water loading as affected by chemistry, soils, climate and management. Proc., Amer. Water Resour. Assoc. Conf., Transferring Models to Users. Denver, CO., Nov. 1990. pp. 187-197.

ABSTRACT: The GLEAMS model was developed as an extension of an earlier USDA model, CREAMS. Both models simulate soil water balance and surface transport of sediments and chemicals from agricultural field management units. GLEAMS, in addition, simulates chemical transport in and through the plant root zone. Several other features were added such as irrigation/chemigation options, pesticide metabolite tracking, and software to facilitate model implementation and output data analysis. Because of its comprehensiveness, ease of implementation and user support, GLEAMS is widely used by researchers, state and federal agencies responsible for water quality programs, the agrichemical industry, and others. Input requirements for the model include daily rainfall volumes, crop and management parameters; soil and physical parameters for soil detachment and transport; pesticide property data such as solubility, expected half-life in soil and/or on foliage, and adsorptivity; and soil physical data by horizon to route water and chemicals. Output data includes, but is not limited to, water, sediment, and pesticide masses in runoff, volumes of water percolated through the root zone, masses of pesticide percolated, and irrigation volumes required. Output frequency can be by day, month, or year. Daily or storm outputs also provide data on distribution of pesticide within the root zone. Several examples of model application to agricultural management systems are illustrated.


Leonard, R. A., W. G. Knisel, F. M. Davis, and A. W. Johnson. 1990. Validating GLEAMS with field data for fenamiphos and its metabolites. Amer. Soc. of Civil Engineers, J. of Irr. & Drain. Engr. 116(1):24-35.

ABSTRACT: The GLEAMS model was modified to simulate the generation and degradation of pesticide metabolites. Translocation of the metabolites within and through the root zone is considered. The modifications have been verified and preliminary validation has been made using field data. The paper presents the model concepts for metabolite generation and degradation. Results of model simulations for fenamiphos metabolite concentrations in the root zone are compared with observed concentrations from a research location in the Georgia coastal plain. These additions to GLEAMS will be helpful to model users working with those nonvolatile pesticides that have toxic metabolites with mobility and persistence characteristics differing from those of the parent compounds. Soil samples are taken periodically during the cropping season at depths corresponding to the GLEAMS model computational layers. The samples are analyzed for fenamiphos and its metabolites for comparison with model simulations. Field observations of metabolite mobility and persistence are compared with limited data in published literature.


Knisel, W. G., R. A. Leonard, F. M. Davis, and J. M. Sheridan. 1991. Water balance components in the Georgia Coastal Plain: A GLEAMS model validation and simulation. Journal of Soil and Water Conservation, 46(6):450-456.

ABSTRACT: Results of the GLEAMS model hydrology simulation were compared with observed data for a small watershed in the Coastal Plain near Tifton, Georgia. A 10-year simulation revealed that only slight improvement resulted from fine-tuning initial estimates of four sensitive parameters. Updating mean monthly temperature and radiation or mean daily temperature input each year did not improve the simulated water balance components compared with observed values. The same results would not be expected in climatic regions where snowmelt and frozen soil occur. Initial parameter estimates would have given entirely satisfactory results for model application in evaluating alternative management systems. Although model calibrations is not required, comparisons with observed data are recommended when possible.

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Leonard, R. A., W. G. Knisel, F. M. Davis, and C. C. Truman. 1991. Application of the GLEAMS model at the Plains, Georgia, agricultural-management site. Proceedings of the U. S. Geological Survey Toxic Substances Hydrology Program, Monterey, California, March 11-15, 1991. USGS Water-Resources Investigations Report 91-4034. pp. 601-604.

ABSTRACT: In 1988, the U.S. Geological Survey; the U.S. Department of Agriculture, Agricultural Research Service; the U.S. Environmental Protection Agency; and the University of Georgia began a cooperative study of chemical transport in a representative agricultural management system near Plains, Georgia. A major objective was to establish data bases for interagency model testing and evaluation. The U.S. Department of Agriculture team of the Southeast Watershed Research Laboratory, Tifton, Georgia, through development and testing of the GLEAMS model, is providing a tool specifically aimed at questions associated with soil, management, and climatic variables in the root zone. The GLEAMS model was successfully tested with the limited data currently available and the model applied to a number of practical questions.


Leonard, R. A., C. C. Truman, F. M. Davis, and W. G. Knisel. 1991. Soil-pesticide grouping for water quality management. Proceedings, Amer. Soc. of Civil Engineers, International Ground Water Symp., Nashville, Tennessee, July 29-August 2, 1991. pp. 262-267.

ABSTRACT: Pesticide and soil properties contribute to changes in runoff and ground water quality. Because pesticides have been found in runoff and ground water, those managing water quality need tools to evaluate surface and groundwater vulnerability to pesticides in complex pesticide/soil/climate/management scenarios. The purpose of the study was to demonstrate an approach for creating data bases to use in soil-pesticide vulnerability maps and other management decision-aids. The GLEAMS model was used to compare different soil and pesticide properties. Nine soils from the Southeastern Coastal Plain were grouped by series based on 3 surface and 7 subsurface textural classes. The grouping system was tested for potential pesticide loss by runoff, sediment, and percolation.


Knisel, W. G., R. A. Leonard, and F. M. Davis. 1992. Simulating processes in nonpoint source pollution. In: J. J. Swain, D. Goldsman, R. C. Crain, and J. R. Wilson (Eds.) Proceedings of the 1992 Winter Simulation Conference, Arlington, Virginia. pp. 1159-1165.

ABSTRACT: The paper describes development of a mathematical model to evaluate nonpoint pollution from diffuse agricultural and forestry sources. Although the model includes numerous physical and chemical processes, a generalized flow chart is used to present the entire system along with more detailed components. The nitrogen cycling and pesticide elements of the chemistry components are presented. The interactions of complex processes are described relative to climate, soil, and agricultural management practices.


Leonard, R. A., C. C. Truman, W. G. Knisel, and F. M. Davis. 1992. Pesticide runoff simulations: Long-term annual means vs. event extremes. Weed Technology, 6:725-730.

ABSTRACT: The GLEAMS model is used to illustrate model application in evaluating potential pesticide runoff of two similar pesticides from one soil. This limited application was chosen for simplicity in illustrating relationships between annual means and single events. When using annual totals of simulated pesticide runoff for comparing two pesticides or assessing risks, long-term 50-yr simulations are preferable to short 10-yr simulations. When short-term simulations are performed care must be exercised in selecting representative climatic periods. For short half-life pesticides, as demonstrated in this study, initial rainfall events on or near the day of application will often contribute most to annual pesticide lost. In these cases, single event analysis may be required. Procedures are demonstrated for expressing annual total pesticide losses and single rainfall event losses probabilistically in terms of expected recurrence intervals.


Workman, S. R., A. D. Ward, and W. G. Knisel. 1992. Assessing the leaching potential of herbicides at the Ohio MSEA. Proceedings, Amer. Soc. of Civil Engrs., Irr. & Drain. Specialty Conf., July 1992. pp. 413-418.

ABSTRACT: The GLEAMS model was used to assess the potential for herbicide leaching at the Ohio MESA. Input data, typical of the Ohio MESA, was used in conjunction with precipitation data for the period 1986-1992. Leaching occurred primarily in the winter months following chemical application with peak concentrations of 35 ppb atrazine being simulated at the bottom of the root zone for a low organic matter soil. Simulated atrazine concentrations rarely exceeded 1 ppb for a typical high organic matter soil. Simulated leaching potential of alachlor was low due to its chemical characteristics. Preliminary field observations from May 1991 are presented. Atrazine and alachlor were detected at a depth of 0.3 m within three weeks of chemical applications despite low rainfall during this period.


Nutter, W. L., W. G. Knisel, P. B. Bush, and J. W. Taylor. 1993. Use of GLEAMS to predict insecticide losses from pine seed orchards. Environ. Tox. and Chem. 12:441-452.

ABSTRACT: Intensive pine forest management practiced in the southern U.S. relies heavily on seed orchards to produce genetically improved seedlings to achieve high productivity. On of the most critical problems is the control of seed and cone insects requiring heavy and frequent applications of insecticides. Hydrologic modeling of insecticide fate in surface water and ground water is a useful technique for evaluating the environmental fate of the applied insecticides. The GLEAMS model was used to evaluate the differences between fate of insecticides at four pine seed orchard sites in different physiographic regions of the southern U.S. A 50-yr simulation period was used. Insecticides selected for simulation were carbofuran, azinphosmethyl, fenvalerate, and permethrin. The simulation of insecticide losses in storm flow and percolate at each of the seed orchards demonstrated the importance of the time of application relative to precipitation occurrence, effective rooting depth, and soil-water conditions. Although the absolute insecticide losses may not be accurately simulated by GLEAMS, the model can predict the seasonal patterns of loss and relative loss among different insecticides likely to occur under actual seed orchard conditions.


Knisel, W. G. (Ed.). 1993. GLEAMS Groundwater Loading Effects of Agricultural Management Systems, Version 2.10. Dept. Publication No. 5, Biological & Agricultural Engineering Department, University of Georgia-Coastal Plain Experiment Station, Tifton. 260 pp.

ABSTRACT: The publication describes the improved mathematical model to assess the effects of climate-soil-management interactions on edge-of-field and bottom-of-root-zone water quality loadings. GLEAMS is an extension of CREAMS with an enhanced hydrology component, a component for vertical flux of pesticides, and a comprehensive plant nutrient component. Parameter editors are available for user convenience in micro-computer applications. The publication is presented in three parts: Part I, model documentation; Part II, model validation; and Part III, user manual.

allpdfs.zip BAED Pub No. 5 (GLEAMS v 2.10 manual in pdf format)


Smith, M. C., W. G. Knisel, J. L. Michael, and D. G. Neary. 1993. Simulating effects of forest management practices on pesticide losses with GLEAMS. Proc. of the International Symp. on Runoff and Sediment Yield Modelling, September 14-16, 1993, Warsaw, Poland. pp. 157-162.

ABSTRACT: The GLEAMS model pesticide component was modified to simulate up to 245 pesticides simultaneously, and the revised model was used to simulate pesticide application windows for forest site preparation and pine release. Fifty-year simulations were made for soils representing four hydrologic soil groups in four climatic regions of the southeastern United States. Five herbicides commonly used in the region to control competing vegetation were represented in the model study. Within the application windows for each herbicide, the best application dates, or "environmental" windows were determined to minimize environmental effects for each location. Results of the simulation study are tabulated in the paper for use in the forest industry.


Shirmohammadi, A., and W. G. Knisel. 1994. Evaluation of the GLEAMS model for pesticide leaching in Sweden. J. Environ. Sci. Health, A29(6):1167-1182.

ABSTRACT: The complexity and expensive nature of experimental procedures necessitate the use of mathematical models for evaluating the fate of agricultural chemicals as they enter into the soil and plant system. However, a transport model should be calibrated and validated for varying climatic, soils, geologic, and land use scenarios before it can be used with acceptable levels of confidence. Leaching data from lysimeter experiments conducted in Mellby soil near Uppsala, Sweden were used to calibrate and validate the Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) model. Although this model is a field-scale model for evaluating the relative impacts of agricultural management systems on surface and groundwater quality, it was put to the test for a leaching study through lysimeters. The results indicated that the GLEAMS model is capable of predicting both water and pesticide leaching through lysimeters in a reasonable manner. The study also concluded that any variability in GLEAMS predictions may be forgiven considering the variabilities that were observed in the measured data. It was also observed that GLEAMS does not perform well in partially freezing temperatures during a given computation day. This resulted in discrepancies between model simulations of drainage compared to those observed in colder periods during the experiment.


Knisel, W. G., and J. R. Williams. 1995. Hydrology components of CREAMS and GLEAMS models. In: V. J. Singh (Ed.) Computer Models of Watershed Hydrology. Chapter 28. pp. 1069-1114.

ABSTRACT: The hydrology components of the CREAMS and GLEAMS water quality loading models are described. A daily rainfall option using a modification of the USDA-SCS curve number method is the preferred runoff-estimating procedure of CRAMS, but the modified Green-Ampt infiltration option is also described. A revised soil layering procedure to better represent the soil profile was incorporated in the daily rainfall procedure of CREAMS that is described as the principal component of GLEAMS.


Knisel, W. G., R. A. Leonard, and F. M. Davis. 1995. Representing management practices in GLEAMS. Eur. J. Agron. 4(4):499-505.

ABSTRACT: Agricultural and forestry management practices may adversely affect surface and groundwater quality. The GLEAMS model was developed to assess management effects on edge-of-field and bottom-of-root-zone loadings of water, sediment, and chemicals. Management systems may affect one or more of the four model components: hydrology, erosion, pesticides, and plant nutrients. Each component is briefly described, and parameter sensitivity is discussed. The effects of changing management practices are soil and climate dependent, but generalized effects are presented. Effects of crop rotation, terracing, irrigation, and tillage practices on hydrologic response, and their impact on erosion, pesticide fate, and plant nutrient losses are summarized in a table. Effects of timing and application methods for pesticides, inorganic fertilizer, and animal waste are also discussed.


Leonard, R. A., W. G. Knisel, and F. M. Davis. 1995. Modeling pesticide fate with GLEAMS. Eur. J. Agron. 4(4):485-490.

ABSTRACT: The pesticide component of the GLEAMS model was developed to evaluate the complex interrelationships among pesticide and soil properties, management alternatives, and climate using long-term simulations. GLEAMS resulted from an enhancement of the CREAMS model to allow simulation of pesticide transport within and through the plant root zone in addition to transport in surface runoff from field-sized areas. The pesticide sub-model is operated with daily inputs from the hydrology and soil erosion sub-models. Pesticide input parameters are required to specify application rates, dates and methods and the properties of the chemical. Outputs are pesticide concentrations and mass in runoff water and attached to transported sediments, pesticide mass leached below the root zone, and pesticide distribution with depth in the root zone. Multiple applications of up to 10 different pesticides can be simulated simultaneously for periods of up to 50 years. The model also considers pesticide metabolites produced by sequential first-order reactions and plant uptake of pesticides. Application methods simulated may be soil surface application, soil incorporation, soil injection, foliar application, or through irrigation water. Values for pesticide soil half-life, foliar half-life, foliar wash-off potential, solubility, and Koc (sorption coefficient for soil carbon) may be obtained from the internal data base or supplied by the user if more specific information is available.


Smith, M. C., W. G. Knisel, D. L. Thomas, and S. R. Wilkinson. 1995. Representing poultry litter management with GLEAMS. Proc. of the Amer. Soc. of Civil Engrs. '95 International Conf. on Water Resources Engineering/Watershed Symposium, San Antonio, Texas, August 14-18, 1995. pp. 446-450.

ABSTRACT: The GLEAMS model was applied to represent 6 fertilizer an d broiler litter management practices on Coastal bermudagrass with multiple cuttings for hay at Watkinsville, Georgia. Observed data from a 7-year study were used to validate GLEAMS with comparisons of runoff volumes, runoff nitrogen, NO3-N leached, forage yield, and nitrogen yield. Simulated runoff volumes and runoff nitrogen losses compared well with observed values for the record period. NO3-N leached and maximum monthly weighted concentrations were compared with good representation of the timing of peaks for all treatments. The model over-estimated the mass of NO3-N leached, but peak concentrations were both over- and under-estimated. Forage yield was simulated very well, but potential yield was found to be a very sensitive model input parameter. The model under-estimated nitrogen yield in the forage very significantly. The optimum nitrogen concentration relations under-estimated N demand, but coefficients for lush nitrogen uptake were very sensitive interactively with potential yield. Lush nitrogen uptake could result in nitrogen deficiency and cause reduced yield which does not occur in observed data.


Michael, J. L., M. C. Smith, W. G. Knisel, D. G. Neary, W. P. Fowler, and D. J. Turton. 1996. Using a hydrologic model to determine the most environmentally safe windows for herbicide application. New Zealand J. of Forestry Science, 26:288-297.

ABSTRACT: A modification of the GLEAMS model was used to determine application windows which would optimize efficacy and environmental safety for herbicide application to a forest site. Herbicide/soil partition coefficients were determined using soil samples collected from the study site for two herbicides (imazapyr, Koc=46; triclopyr ester, Koc=1038) and published values for two other herbicides (hexazinone, Koc=54; triclopyr amine, Koc=20) were used in the model. Other site-specific characteristics were taken from catchment topographic maps and soil data. Long-term climatic records for the region were then use to provide meteorological data for use in the hydrology component of the model. The model was run with herbicide application for each day of the manufacturers' recommended growing-season application windows. Average surface run-off losses, expressed as a percentage of applied, were low for all herbicides modeled (hexazinone, 0.37%; imazapyr, 0.34%; triclopyr amine, 0.21%; triclopyr ester 1.85%). Model predictions of herbicide loss for each application day were then summarized and the application days with the lowest predicted loss within the manufacturers' application windows were identified as the environmentally safest days (environmental window) for application. This application of the GLEAMS model predicts an environmental window, for each herbicide for the site under consideration, during which the probability of adverse environmental impacts is at the lowest level achievable based upon long-term climatic records. The environmental window for pesticides other than herbicides can also be determined through modeling in a similar fashion. GLEAMS is the model chosen for this example, but other pesticide fate models may be equally applicable.


Morari, F., and W. G. Knisel. 1997. Modifications of the GLEAMS model for crack flow. Trans., Amer. Soc. of Agric. Engrs., 40(5):1337-1348.

ABSTRACT: The GLEAMS model version 2.10 was modified to represent water and solute movement in cracking clay soil. The modification consists of including GLEAMS subroutines to estimate the main processes affecting the phenomena: cracking dynamics in soil, initiation of crack flow, crack flow, concentration of solutes in the crack flow, and transportation through the cracks. Theory for the hydrologic and chemical modifications is presented with model evaluation using data from two experimental sites: at Vallevecchia di Caorle, Italy and Riesel, Texas, USA. There was considerably more water redistribution and solute movement out of the root zone with simulated crack flow compared with simulations with the unmodified model. Metolachlor and terbuthylazine, observed in shallow groundwater at the location in Italy, were simulated to leach out of the root zone with the modified model whereas the unmodified version did not simulate leaching. Simulated chemical runoff differed between the two models: the crack flow modifications resulted in less total pesticide losses because simulated concentrations were lower in the surface soil layer and runoff volumes were less.


Shirmohammadi, A., B. Ulen, L.F. Bergstrom, and W.G. Knisel. 1998. Simulation of nitrogen and phosphorus leaching in a structured soil using GLEAMS and a new submodel, "PARTLE". Trans. Amer. Soc. Of Agric. Engrs., 41(2):353-360.

ABSTRACT: The potential negative impact of agricultural chemicals on the quality of surface and ground water resources is a worldwide concern. The complexity of factors affecting non-point source pollution makes experimental assessment of the environmental consequences for different management strategies laborious and expensive. Therefore, one feasible method is to use the existing research database to validate and modify the computer models, then use the models to simulate the long-term impact of these systems. In this study the hydrologic and nutrient loss data from a subsurface drained, structured clay soil in southwest Sweden was used to examine the applicability of GLEAMS to simulate the drainage discharge and N and P concentrations in the discharge water. The results indicated that GLEAMS was capable of simulating drainage discharge, nitrate-N losses and dissolved-P losses reasonably well, but there were no algorithms to simulate the particulate-P losses via drain tiles. Therefore, a sub-model, "PARTLE" was developed and tested. Our results indicate that the PARTLE sub-model, in association with the GLEAMS model, provided reasonable estimates of particulate-P loss via drainage in this soil. The study concluded that considering the impact of preferential flow and the ratio of annual drainage discharge to annual precipitation is necessary for proper predictions of particulate-P in structured soils.


Knisel, W. G., and E. Turtola. 1999. GLEAMS model application on a heavy clay soil in Finland. Agricultural Water Management, 43(3):285-309.

ABSTRACT: The GLEAMS model version 2.10 was calibrated and validated with data from research plots on illitic clay soil near the Agricultural Research Centre at Jokioinen, Finland. Observed surface runoff, drainage flow, erosion, and associated nitrogen and phosphorus loads from 0.46 ha plots were used in the model application for a 7-year period with different management practices. Two plots were used for calibration and two plots were used for validation in the present study. The model was found to represent the soils and management with adjustment, or fine tuning, of sensitive parameters. The simulated runoff, percolation, evapotranspiration, amount of soil erosion, phosphorus (P) and nitrogen (N) losses in runoff and drainage water compared very well with observed values on the average, but differed considerably from year-to-year and especially month-to-month. Observed data were required after improved drainage installation in order to adjust parameters sensitive in water balance calculations. The P component of the model gave better estimates of losses in runoff and with eroded soil particles than did the more complex N component. P with particulate in drainage water was simulated externally since it is a significant part of the total P lost and it is not considered in the model. Some model modifications were made to better represent the climatic conditions of Finland. The validation study indicated that GLEAMS can be used satisfactorily in Finland for comparisons of alternate management practices as recommended by the model developers.


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