Water Resources Research

Estimating fluvial sediment transport: The rating parameters


  • James P. Syvitski,

  • Mark D. Morehead,

  • David B. Bahr,

  • Thierry Mulder


Correlations between suspended sediment load rating parameters, river basin morphology, and climate provide information about the physical controls on the sediment load in rivers and are used to create predictive equations for the sediment rating parameters. Long-term time-averaged values of discharge, suspended load, flow duration, flow peakedness, and temporally averaged values of precipitation, temperature, and range in temperature were coupled with the drainage area and basin relief to establish statistical relationships with the sediment rating parameters for 59 gauging stations. Rating parameters (a and b) are defined by a power law relating daily discharge values of a river (Q) and its sediment concentration Cs, where Cs = aQb. The rating coefficient a (the mathematical concentration at Q = 1 m3/s) is inversely proportional to the long-term mean discharge and is secondarily related to the average air temperature and the basin's topographic relief. The rating exponent b (the log-log slope of the power law) correlates most strongly with the average air temperature and basin relief and has lesser correlations with the long-term load of the river (which is related to basin relief and drainage area). The rating equation describes the long-term character of the suspended sediment load in a river. Each river undergoes higher-frequency variability (decadal, interannual, and storm event) around this characteristic response, controlled by weather patterns and channel recovery from extreme precipitation events.