Temporal variations of suspended sediment transport in Oneida Creek watershed, central New York

SummaryUsing event-based suspended sediment data collected from 2008 to 2010 in a medium-size agricultural watershed in Central New York, we first examined the statistical properties of suspended sediment concentration, C and the associated water discharge, Q. Next, we identified two different transport processes in two discharge ranges separated by a different threshold Qt for each season. Different exponents of sediment rating curves (SRCs) in each season revealed that sediment was transported near capacity during lower discharges but well below capacity during higher discharges. The persistence of these two trends in all seasons suggested that suspended sediment transport was generally supply limited. Sediment loads predicted by a single seasonal SRC are similar to those predicted by the two separate SRCs for above and below Qt, which suggests that the two transport processes are not significantly different and seasonal sediment transport may be described by a single SRC. The better fit of SRC for the combined 3-year data compared to those for individual years indicates that seasonal changes of suspended sediment transport are limited and the transport dynamics that emerge at shorter time scales (i.e., event and season) are effectively averaged out. We then calculated sediment yields for 3 years using a process-based SRC method: annual hydrograph was divided into storm and base flows using values of Qt for all seasons and only storm flows were used to calculate sediment yields based on the developed SRCs. Comparing sediment yields of 3 years calculated using three seasonal SRCs to those using the combined 3-year SRC indicated that the discrepancies between the two were less than 5%, suggesting that sediment yield may be accurately estimated using the single combined-year SRC. Finally, we discussed the appropriate sampling strategy in the region and demonstrated geomorphological nature of sediment transport based on the calculated effective discharges and cumulative sediment loads.

► The exponent of a sediment rating curve reflects the degree of sediment supply.
► Short-term sediment variations can be averaged out at longer time scales.
► A process-based approach for seasonal sediment loads and sediment yields.