Particle size distributions (PSDs) of suspended particulate matters in a coastal zone are lognormal and multimodal in general. The multimodal PSD, which is caused by the mixing of multiple particle and aggregate size groups under flocculation and erosion/resuspension, is a record of the particle and aggregate dynamics in a coastal zone. Curve‐fitting software was used to decompose the multimodal PSD into subordinate lognormal PSDs of primary particles, flocculi, microflocs, and macroflocs. The curve‐fitting analysis for a time series of multimodal PSDs in the Belgian coastal zone showed the dependency of the multimodality on (1) shear‐dependent flocculation in a flood and ebb tide, (2) breakage‐resistant flocculation in the spring season, and (3) silt‐sized particle erosion and advection in a storm surge. Also, for modeling and simulation purposes, the curve‐fitting analysis and the settling flux estimation for the multimodal PSDs showed the possibility of using discrete groups of primary particles, flocculi, microflocs, and macroflocs as an approximation of a continuous multimodal PSD. Key Points Decomposition of the multimodal PSDs to the subordinate unimodal lognormal PSDs Investigation on particle/floc dynamics in a coastal zone Identification of primary particles, flocculi, microflocs, and macroflocs