River sediment, fine sand / silt interface sensing

For a column of river sediment I want to measure fine sand / silt interface and perform analog control. So far I could not find a sensor to do this and resorted to density control for the moment. Density control (DT-1/DIC-1) SK-5A may work for recent tank collection? Any thoughts are greatly appreciated. Attached is a concept to collect sediment with dissolved fertilizer returning to the river and any thoughts on this concept is also appreciated.