Return flows in large rivers associated with navigation traffic Bhowmik, N. G., B. S. Mazumder, and T. W. Soong. 1992. Return flows in large rivers associated with navigation traffic. Pages 760-765 in Marshall Jennings and Nani G. Bhowmik, editors. Proceedings, Water Forum '92, Hydraulic Engineering Sessions of the American Society of Civil Engineers, Baltimore, Maryland, August 2-6, 1992. Reprinted by U.S. Fish and Wildlife Service, Environmental Management Technical Center, Onalaska, Wisconsin, February 1993. EMTC 93-R022. 6 pp. (NTIS #PB94-113594) ABSTRACT Movement of barge traffic (barge tows) in restricted waterways such as the Illinois or Mississippi Rivers can generate rapid return flows and water-level depressions (drawdown) between the barge and the shoreline. Due to this return flow, velocity distribution in the zone between the barge and the shore changes temporarily in space and time. The return velocity and the drawdown generated by barge traffic depend on many factors, including river width and depth, barge characteristics, tow speed, draft, and lateral distance from the barge to the shore. An overall mathematical modeling concept of the lateral variation of return flow due to navigation traffic is discussed in this paper. The x- and y-components of velocity data were collected by installing two- dimensional electromagnetic current meters along a cross-section of the river from the shore to the barge. Few methods are available in the literature to calculate the shape of the lateral velocity distribution created by the barge passage, and these methods indicate an exponential velocity distribution from the barge to the shore. However, field velocity data show that when a barge moves either upstream or downstream, return velocity becomes most pronounced at a point one-fourth the width of the river from the shore. At this zone at the mid-section between the barge and the shore, velocity is almost zero. Therefore, the width of the channel between the barge and the shoreline has been subdivided into two vertical columns for the present analyses. The lateral velocity distribution from the shore to the one-fourth point of the width follows a parabolic distribution in which water moves in the opposite direction of the barge. For the zone between the barge and the one-fourth point of the width, velocity decreases almost linearly with distance, becoming zero at the one-fourth point. Based on this field data, a lateral velocity profile is postulated. KEYWORDS return flows, navigation, barge traffic, Illinois River, Mississippi River