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elevation, and extent of flat-lying depositional surfaces that might be either the active flood plain or terraces. Coordinate data from the total station were downloaded to a personal cDmputer for analysis. A technician then used the coordinate data to hand plot a map of the study site at a I :400 scale. The hand drawn contour lines were then digitized into a geographic information system using a digitizing table and Arc/Info software. Once digitized, controll'oints in each map segment were assigned coordinate values in a local grid system. Each line segment (arc) and enclosed polygon was assigned attributes according to what each represents on the map. Identifying bankfull discharge and the active flood plain The active flood plain is defined as the flat depositional surface adjacent to the channel that is overtopped during times of flooding and is constructed by the present flow regime. The active flood plain is just overtopped at bankfull discharge. The recurrence interval of the bankfull discharge varies on different rivers. We identified bankfull discharge in the study reach by surveying the elevation of each depositional surface at numerous locations throughout the reach and noting the vegetation on each surface. After plotting these points, a best-fit line was plotted through the surveyed elevations and projected through the gage. The discharge of the flood that inundates each surface was determined from the elevation of the line where it passes through the rating relationship at the gage. We identified three different flat surfaces adjacent to the channel within the study reach that might have been the active flood plain. The active flood plain was distinguished from low elevation terraces by choosing the lowest widespread depositional surface that is inundated by frequent low magnitude 11