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Traveltime and Dispersion of Contaminants in the cJ7~ ,7 Vampa River from Steamboat Springs to the Green River, Northwestern Colorado -J.E. Vail! INTRODUCTION In the event of a hazardous material spill into a river, traveltime data for various stream flows provide valuable information about traveltime and dispersion of the hazardous material. In this report, traveltime is defined as the time it takes a contaminant particle to move between known points on a river at a constant streamflow. Peak concentration can be defined as the maximum amount of a given substance per volume of water. Streamflow traveltimes and dispersion characteristics for the Yampa River were determined by two U.S. Geological Survey studies. Bauer and others (1979) presented traveltime information for the Yampa River from Steamboat Springs to Craig, Colorado. Ruddy and Britton (1989) presented traveltime information for the Yampa River from Craig to the confluence with the Green River (fig. 1). The results of these two investigations are summarized in this report. Also presented are equations used to predict the traveltime of the leading edge and the trailing edge of a hazardous material cloud and the most probable peak concentration (Jobson, 1996). This report was prepared under the U.S. Geological Survey/ National Park Service Water-Quality Partnership. When a hazardous material spill occurs, traveltime information can be used to answer the following questions: · When will the peak concentration of the spill arrive at a given point in the river? · When will the leading edge of the spill arrive at a given point in the river? · What will the peak concentration be at a given point in the river? · When will all of the contaminant pass a given point in the river? HOW TO DETERMINE ARRIVAL TIME OF PEAK CONCENTRATION To address the questions listed above, follow these six steps: Step i.-Determine the streamflow at the location of the spill by using figure 1 and the nearest streamflow-gaging station listed in table 1. Streamflow information for the U,S, Department of the Interior U,S. Geological Survey streamflow-gaging stations listed in table 1 can be obtained on the Internet: · U.S. Geological Survey at http://webserver.cr.usgs.gov · Colorado Department of Natural Resources at http://www.dnr.state.co.us/water/jlow · or by telephone-Colorado Division of Water Resources Water Talk number at 303-831-7135 If the streamflow information for the stations listed in table 1 is unavailable from the above sources, the average monthly streamflow listed in table 2 can be used. For example, if a spill occurred in May near Maybell, Colo. (site 17), table 2 would provide the average monthly stream- flow for that site, in cubic feet per second (6,280 ft3/s). Because of ice effect at the streamflow-gaging stations during winter months, the streamflow data provided on the Internet and the Water Talk telephone line might be higher than the actual streamflow. The reported streamflows might then be used to estimate a faster traveltime for a winter spill, thereby providing a margin of safety. Locate the nearest traveltime reference site upstream from the spill by using figure 1 and table 3 and the point of interest downstream. Step 2.-Using the streamflow from step 1 and the sites identified in step 2, determine the traveltime of the peak concentration of the hazardous material by using table 4. If the streamflow determined in step 1 is different from the discharge reported in table 4, interpolate between values that bracket the reported streamflow or use the higher streamflow in table 4. This approach would provide a conservative traveltime. HOW TO DETERMINE THE ARRIVAL OF THE LEADING EDGE Step 3. -Detennine the arrival time of the leading edge of the contaminant by multiplying the traveltime of the peak concentration by 0.89 (Jobson, 1996). USGS WRIR 99-4239 January 2000