Suspended particulate matter (SPM) concentrations in estuaries have been observed to vary strongly over the spring–neap cycle. A systematic framework for analysing the processes causing this SPM variability is missing. In this study we set up such a framework. It is demonstrated using two model cases: an idealised test case and one representative of the Loire estuary. Using this, we explain the locations and timing of maximum concentrations in terms of the governing physical mechanisms.