Abstract |
- Variation in fluvial suspended sediment–discharge behavior is generally thought to be the product of changes in
processes governing the delivery of sediment and water to the channel. The objective of this study was to infer
sediment supply dynamics from the response of suspended sediment behavior to antecedent hydrologic factors.
The Salinas River (California) is seasonally active, moderately sized, and potentially susceptible to lasting impacts
of hydrologic event history because of aridity, high discharge variability, and in-channel terminating flows. Forty-five
years of suspended sediment data from the lower Salinas and 80 years of hydrologic data were used to construct
hydrologic descriptors of basin preconditioning and to test the effects of these preconditions on suspended
sediment behavior. Hydrologic precondition factors — including change in mean daily discharge and increasing
elapsed time since the last moderate discharge event (~10–20 times mean discharge (Q[subscript mean])) — were found to
have significant positive effects on discharge-corrected, fine suspended-sediment concentrations. Conversely, increased
elapsed time since the last low discharge event (~0.1–0.4 times Q[subscript mean]), and the sum of low flow conditions
over interannual time scales were found to cause significant negative trends in fine suspended sediment
concentration residuals. Suspended sand concentrations are suppressed by increased elapsed time after threshold
discharges of ~0.1–2 and 5–100 times Q[subscript mean], and increased low to no flow days over time scales from 1 to
2000 days. Current and previous year water yield and precipitation magnitudes correlate positively with sand
concentration. Addition of fine sediment from lower Salinas hillslope or channel sources on the rising limb of
the hydrograph is the major mechanism behind an overall positive hysteretic pattern, which was forensically
supported by the annual occurrence of in-channel suspended sediment deposition by early season, channel terminating
flows and by the flushing function of moderate hydrologic events found in this study. The importance of
hillslope and/or channel fine sediment contributions proximal to the lower Salinas are further highlighted by the
lack of control exerted by upper subbasin water provenance on fine suspended sediment concentration, while
sand behavior is differentiated by upper basin water provenance. Investigation of suspension of bed-sized sediment
showed that the channel bed could exert significant effects on fine and sand-sized suspended sediment dynamics,
but this mediation for fine sediment was most likely small in terms of decadal-scale sediment budgets.
The magnitude of the effects of hydrologic variables on sediment dynamics remains uncertain, but the factors
identified here may play a significant role in water quality, if not long-term sediment flux to the ocean.
- Keywords: Rating curves, Antecedent conditions, Arid rivers, Suspended sediment transport, Small mountainous rivers
- Keywords: Rating curves, Antecedent conditions, Arid rivers, Suspended sediment transport, Small mountainous rivers
- Keywords: Rating curves, Antecedent conditions, Arid rivers, Suspended sediment transport, Small mountainous rivers
- Keywords: Rating curves, Antecedent conditions, Arid rivers, Suspended sediment transport, Small mountainous rivers
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