Water Quality Models for Watershed Management

Abstract

Several water quality models are available for use in assessing the effects of agricultural management on the environment. Since these models are being used to solve a variety of water quality problems, they vary considerably in structure and complexity. For example, simple screening models may be adequate and appropriate for identifying potential pollutant sources. However, more comprehensive models are needed in comparing agricultural management effects on chemical transport by runoff and sediment. Model requirements may also vary depending upon temporal and spatial scales, cost, and risk associated with proposed projects.Some of the most widely used water quality models, particularly those most useful in agricultural management are described briefly. Two of the models, the Erosion-Productivity Impact Calculator (EPIC) and the Simulator for Water Resources in Rural Basins (SWRRB), are presented in more detail to serve as examples of field and watershed scale water quality models. These models were selected because they feature convenient and comprehensive agricultural and soil management components. For example, EPIC is useful in solving management problems involving crop varieties and rotations, tillage, furrow diking, irrigation, drainage, fertilization, pest control, weather variation, atmospheric CO2 concentration, erosion (wind and water), water quality (nutrients and pesticides), manure handling, crop residue management, liming, and grazing. The model operates on a daily time step and is capable of simulating hundreds of years if necessary. It is also useful in solving short term (within growing season) management problems operating in a real time mode. The SWRRB model was designed for solving watershed scale problems like water supply and quality (nutrients and pesticides), pond and reservoir design, groundwater flow contributions, irrigation water transfer, and stream channel routing of sediment and agrichemicals. SWRRB also operates on a daily time step and allows watershed subdivision. Subdivisions are made to account for spatial variability of soils, land use, weather, and topography. This gives SWRRB the capability to estimate off-site impacts including channel and reservoir deposition and total water supplies. Example applications of EPIC and SWRRB to water quality problems are also described.KeywordsSediment YieldRunoff VolumeWatershed ManagementWater Quality ModelStream PowerThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.