This is not realy  anymore the Senne here. It's the first vaulting from 1871. It's now used by Vivaqua as storm basin and can be used sometimes as derivative from Aviation. But ALL the flow of the river is going to https://www.openstreetmap.org/way/785901894 

https://metro3.be/fr/article/06-08-2021/travaux-dans-lancien-pertuis-de-la-senne-sous-le-boulevard-lemonnier

https://www.coordinationsenne.be/downloads/La-Senne-souterraine.pdf

So maybe canal or stream is better than river ? Or maybe Ditch ? 

Notice that NGI and Bruxelles environnement don't  mention this way as river or water line at all.