Where the shape comes from
Three parallel strokes for the banks and the flow of a river seen from above, a simplification of the more elaborate wave-lines of 水. Sandbars rising in mid-current, dotted along the same three strokes, give 州, a river island that grew into the word for an administrative region or state; walking its length along the banks gives 巡, to patrol; and 训, to instruct, uses it only for its sound.
汉字 filed under 川
No published character on HSK Guide is filed under this radical yet. 汉字库.