Event-based suspended sediment dynamics in a central New York watershed

Using discharge and sediment data collected from 23 events between 2008 and 2010 in a 311-km2 watershed of central New York, we investigated event sediment dynamics of the studied watershed. After showing the statistical difference of the data in different seasons, we examined the detailed hysteresis patterns of all events. Spring events had figure eight with anticlockwise (figure-8/AC), clockwise (C), anticlockwise (AC), and complicated patterns. Summer events had C, AC, figure-8/AC, figure-8/C, and complicated patterns. Fall and winter events had the same patterns as those in summer, as well as a weak loop pattern. The diversity of patterns within and between seasons suggests that detailed processes of sediment transport were not only complicated during one event but also varied from season to season. Although hysteresis analysis failed to identify these detailed processes and the associated sediment sources in such a relatively large watershed, it successfully revealed a common feature dominating the transport processes: event sediment transport was generally supply limited. Further analysis on the correlation between event sediment yield (SSYe) and event peak discharge (Qpeak) indicated that (i) events with clockwise patterns tended to have more SSYe than those with other patterns for the same Qpeak and (ii) data from all events may be statistically well described by a single SSYe–Qpeak equation, regardless of hysteresis patterns. This equation (i) reveals that complicated event transport processes may be lumped into a simple process over events and (ii) reflects the general supply-limited nature identified by hysteresis analysis. Using this equation and the magnitude–frequency analysis, we further discovered that in the past 21 years, sediment was mainly transported by more frequent but relatively small discharges with the recurrence interval no more than 0.5 year.