I certainly hope someone with more experience in subaqueous soils can weigh in on your question regarding settings that are intermittently dry (semi-permanently subaqueous) on a long cycle. The best defense at this time for lack distinction of such soils is our lack of thorough investigation and mapping of such soils. We hope, in the near future, to begin workshops and to fund activities to advance the investigation and mapping of subaqueous soils and plant communities, and of course their classification in Soil Taxonomy.