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.
Automatic irrigation, manual irrigation, and chemigation options are available.
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.
Gleams has been revised for year 2000 compliance. It has long been recognized that GLEAMS was not Y2K compliant in that it utilized a 2-digit year and considered leap year every 4 years irrespective of century. Model users requested that the model be made Y2K compliant in order to maintain it's utility beyond 1999. Some additional features had evolved since the release of version 2.10 in 1993. It was decided to incorporate these features and the Y2K revisions into a new version, V3.0.