So in my further research and investigation, I would say that the term that is used to described for the uncovered soil when river waters recede after floods is called a Silt. I hope you are satisfied with my answer and feel free to ask for more if you have question and clarifications.
When river water recedes after a flood, uncovered soil is usually fertile and suitable for processing and sowing, because water during the flood has left a lot of good materials that make the soil fertile and usable. River floods are usually periodic, ie. they have their cycles during the year, so that people living in these areas know at what time of year and how, they should sow seeds and process such soil. Such surfaces are called alluvial levels, or only the alluvial.
