I am looking for real cases of esturies where sediment material from beaches in their vicinity is trapped. As a result, coastal structures like groynes or ports near such estuaries may possibly suffer from erosion problems as well.
You might wish to look at the attached paper by Flor-Blanco et al. (2013) in Geo-Marine Letters 33. It's the closest to your question that I can think of.
For centuries this is the case in the Wester- and Oosterschelde estuaries in the Netherlands and also the Wadden Sea. Banks are protected with stone fills but in the past often bank collapses and flow slides occurred. Recent examples of beach collapse in estuaries we found in Queensland, Australia. You can download the papers on my site.