Adam Clarke on Joshua 4:18

The waters of Jordan returned unto their place - It is particularly remarked by the sacred historian, that as soon as the soles of the priests' feet touched the water, the stream of the Jordan was cut off, Jos 3:15, and the course of the river continued to be inverted all the time they continued in its channel; and that as soon as the soles of their feet had touched the dry land, on their return from the bed of the river, the waters immediately resumed their natural course. All this was done by the sovereign influence of that God whose presence was represented by the ark of the covenant.