SUSPENDED SEDIMENT DYNAMICS DURING HYDROLOGICAL EVENTS IN A CENTRAL NEW YORK WATERSHED

Short-term dynamics of suspended sediment transport are still poorly understood in watersheds of central New York. At the outlet of a medium-size agricultural watershed, we collected suspended sediment samples for both snowmelt and rainfall events from 2008 to 2010. By examining the variations of mean and peak event discharges, and mean and peak suspended sediment concentrations among three seasons (i.e., spring, summer, and fall), we identified variable statistical patterns among seasons. Next, we analyzed hysteresis loops of these events in each season using not only the classic visual classification of loops, but also a quantitative index HL. The value of HL was calculated as a ratio of total suspended sediment load in the rising limb(s) of a hydrograph to that in the falling limb(s). HL > 1 infers a clockwise-dominated hysteresis pattern, HL < 1 signifies an anticlockwise-dominated one, and H » 1 indicates no loop. Values of HL can effectively identify whether suspended sediment is mainly transferred from upland hillslopes or from in-channel bed and banks for both simple and complicated hysteresis patterns, as well as different shapes of the same hysteresis patterns. We also compared HL with a different index, HI, which is calculated based on the shape of a loop. Results indicated that hysteresis loops of events were generally dominated by anticlockwise patterns, suggesting suspended sediment transport in all seasons was primarily controlled by sediment supply from hillslopes. Further analysis for event peak discharge (Q_peak) and event sediment yield (SSY_e) revealed that though each season had a different Q_peak – SSY_e relationship, data from all seasons may be reasonably well described by one equation, suggesting seasonal variations of suspended sediment transport in the studied watershed are not significant.