Complex sentence: The Cambodian floodplain or the Mekong Plain is a vast low-lying area traversed by the Mekong river; however, only a relatively small portion of the plain consists of fluviatile deposits of the young Mekong.
Split into simpler sentences: The Cambodian floodplain or the Mekong Plain is a vast low-lying area traversed by the Mekong River. Only a relatively small portion of the plain consists of fluviatile deposits of the young Mekong.