Influences of tides, weather, and discharge on suspended sediment concentration

Abstract

This paper presents an analysis of long-term monitoring datasets to determine the influences of different external forcing mechanisms on suspended sediment concentration in Suisun Bay, CA, and to evaluate the degree of timescale dependence in the forcing mechanisms. Time- and frequency-domain time series analytic techniques were used on 2-year-long datasets of suspended sediment concentration, river discharge, and weather variables. Surface and bottom SSC are very closely linked in winter, but less so in other seasons. Wintertime subtidal SSC variability is controlled by precipitation and river discharge. During summer months, control shifts to another undefined forcing mechanism. Fortnightly and monthly tides control background and tidally-varying SSC. The relationship between wind and SSC is statistically significant at certain frequencies, but the wind effect comprises a very small proportion of total subtidal variability. When tested individually, 80% of the variance in SSC can be explained by tides, 55% by discharge – rain, and 65% by wind. Collectively, however, wind, river discharge, and tides in combination explained up to 75% of the variance in subtidal SSC, with the other 25% comprising noise and unknown variables. There is a moderate amount of timescale dependence in the forcing mechanisms, but the dominant tidal processes are consistently present over many timescales of observation.