Suspended particulate matter concentration in response to tidal hydrodynamics in a long mesotidal floodway

Analyses of seasonal data obtained using acoustic Doppler current profilers provide an understanding of the behavior of suspended particulate matter concentration (SPMC) toward different forcings in tide-controlled floodways. In this work, the relative contributions of external forcings on SPMC variability were quantified in a tidal river system using singular spectrum analysis (SSA). The main environmental features affecting SPMC were identified as i) spring-neap tidal oscillation, ii) the ebb/flood velocities, and iii) tidal straining. Large SPMC fluctuations occurred under strong mixing states and were directly related to the sediment resuspension stirred up by spring-neap tidal cycles (73.6%-81.9%) and ebb/flood velocities (9.6%-19.5%). On the seasonal scale, river discharge is the key variable explaining the downstream flushing and promoting the occurrence of a convergence zone at the floodway. Upstream from the floodway (greater than 4.8 km from the river mouth), the spring-neap tidal oscillation dominated the suspended particulate matter (SPM) mobility under low river discharge. Two interesting findings were revealed in this work: (i) the SPMC/SPM transport variation responses to tidal forcing (tidal asymmetry) were dominated and modified by river discharge and (ii) the effect of river discharge on the SPMC/SPM transport did not result in a uniform state along the floodway. It is believed that these findings provide further understanding of the dynamics of suspended sediments in shallow tidal systems.