It was some time ago I worked there. As the feeder flows through Public Open Space at Blackweir, Bute Park and at the back of the Castle, whilst not belonging to the Council, it formed part of their consciousness as an attractive interesting historical element of the park land. All the staff referred to it as the feeder and the definitive historian of Cardiff Parks Andrew Alexander Pettigrew 1875 - 1936 referred to it as the feeder as well. An interesting family. His work “The Public Parks and Recreation Grounds of Cardiff” is an authoritative reference source- have a look at the enclosed link which gives details of the Pettigrew dynasty
http://www.cardiffparks.org.uk/pettigrew/index.shtml