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<br /> <br />on2546 <br /> <br />DESCRIPTION OF WATER-QUALITY MODELS USED FOR ANALYSIS <br /> <br />Two models were used in the calibration phase of the analysis: A U.S. <br />Geological Survey model and a modified Pioneer-I model developed by Battelle <br />Pacific Northwest Laboratories. The purpose of this comparison was to show <br />any differences in the computational algorithms used in the models for the <br />same model-parameter values. <br /> <br />U.S. Geological Survey Model <br /> <br />The U.S. Geological Survey model is documented by Bauer and' Jennings <br />(1975). The model is based upon the oxygen-sag equation of Streeter and <br />Phelps (1925). The model is intended for use under steady-state (constant <br />flow rate of waste and stream discharges) conditions. When applying the model <br />to a given reach of a river, the reach is divided into a given number of <br />subreaches, generally defined by locations where a waste or tributary inflow <br />mixes with the river water. The formulation assumes complete mixing in a <br />stream cross section. <br /> <br />Some of the original programing concepts made for this form of model <br />been described by Shindala (1972). The first large-scale'application of <br />model was in Arkansas (Jennings and Bryant, 1973). <br /> <br />have <br />this <br /> <br />The original model (Bauer and Jennings, 1975) was expanded to include <br />processes for determining concentrations of fecal-coliform and total-coliform <br />bacteria, the various nitrogen components, and orthophosphate. The equations <br />for determining concentrations of coliform bacteria that were incorporated are <br />those described by Mahloch (1973), equations for nitrification reactions are <br />described by Thomann (1972), and the equation for determining concentrations <br />of orthophosphate is described by Willis, Anderson, and Dracup (1975). <br /> <br />Pioneer-I Model <br /> <br />The Pioneer-I model (Waddel and others, 1973) is based upon the DOSAG-I <br />model, originally developed by the Federal Water Pollution Control <br />Administration and modified by the Texas Water Development Board (1970); The <br />Pioneer-I model, which also utilizes the oxygen-sag equation of Streeter'and <br />Phelps (1925), was developed for stream studies relating to dissolved-oxygen <br />and biochemical oxygen demand dynamics. <br /> <br />The mathematical 'basis of the Pioneer-I model is formulated around <br />concepts of steady-state flow and uses Lagrangian coordinates to determine <br />concentrations of various constituents for a given flow condition, waste- <br />source concentration, water temperature, reaction coefficients, and water- <br />diversion data. The water-quality dynamics usually are characterized by <br />algorithms of first-order differential equations, although some algorithms of <br />this model have the option for using second-order functions. <br /> <br />11 <br /> <br />~ <br />