When " Kemena River" ?

In 1867, the Italian botanist by the name Odoardo Beccari visited Bintulu . Throughout his writings he only referred to the main river in Bintulu as the "Bintulu" river. This begs the question" When did the name " Kemena River" as we now call the main river in Bintulu gained usage? This is an interesting problem that needs further research. Since when and who did change the name from "Bintulu" river to "Kemena" river? We know the meaning of Bintulu river viz from the meaning of "Bintulu". But what about Kemena? What does it mean?