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<br /> <br />002547 <br /> <br />The Pioneer-I model was used in this study by the Colorado Department of <br />Health to compare model results with those obtained with the U.S. Geological <br />Survey model. The Pioneer-I model currently used by the Colorado Department <br />of Health has been further modified with respect to the original Pioneer-I <br />model developed by Battelle Pacific Northwest Laboratories (Waddel and others, <br />1973) for the U.S. Environmental Protection Agency. The additional <br />modifications to the Pioneer-I model were made by the URS/Ken R. White Co. <br />(1975) to facilitate the use of the model in situations where data are scarce. <br />These modifications make it possible to study discrete segments of a river <br />rather than an entire river basin, to add or remove discharges without <br />redefining the entire model, and to allow streamflow in reaches or subreaches <br />of the river to decrease to zero without physically removing these reaches or <br />sub reaches from the model input. <br /> <br />The Pioneer-I model recently has been modified again by the Colorado <br />Department of Health to estimate the concentrations .of the following <br />constituents: Total nitrogen, dissolved solids, metal ions, orthophosphate, <br />fecal-coliform pacteria, ammonia nitrogen, nitrite nitrogen, pitr~te nitrogen, <br />carbonaceous biochemical oxygen demand (CBOD), chlorophyll-a, and dissolved <br />oxygen (DO). <br /> <br />DATA USED FOR MODEL CALIBRATION <br /> <br />Data-Collection Program <br /> <br />Field data used for calibrating the models were collected at 33 sites <br />along the study reach during 24 hours on September 23-24, 1975. Samples were <br />taken at approximately 3-hour intervals. The basic data collected for this <br />study are tabulated in a report by Giles and Brogden (1977). A total of 16 <br />main-stem, 11 tributary, and 6 wastewater-effluent sites were sampled (table 2 <br />and fig. 6). Only 10 of the 17 tributaries in the study reach were sampled <br />because the remainder had flows of less than 0.1 ft3/s (0.003 m3/s). At all <br />sites, field determinations were made for DO, water temperature, specific con- <br />ductance, fecal-coliform and total-coliform bacteria, and pH. In addition, <br />water samples were collected for laboratory analysis of biochemical oxygen <br />demand (BOD), organic nitrogen (nonfiltered form), ammonia nitrogen, nitrite- <br />plus-nitrate nitrogen" Kjeldahl nitrogen, orthophosphate, total phqsphorus, <br />and total nitrogen. At least one discharge measurement was made at each sam- <br />pling site during the 24-hour sampling period. <br /> <br />As stated previously, data for this investigation were collected during a <br />single' 24-hour period. As noted by Rickert and Hines (1975), there is an <br />inverse relationship between the complexity of a water-quality process and the <br />ability to produce useful modeling assessments within a given time span. The <br />Yampa River from Steamboat Springs to Hayden is not extremely complicated with <br />respect to the flow regime or water-quality characteristics. Ideally, data <br />for modeling would be collected during different seasons of a year; however, <br />data collected during critical-flow conditions are sufficient to adequately <br />calibrate a model (Hines and others, 1975). Both flow and water-quality char- <br />acteristics in the study reach normally vary considerably over a yearly cycle. <br /> <br />12 <br />