::snip from BBC wales site:
An element usually comes before the name of the river in place names, as in Castell-nedd (Neath) and Llanelwy (St Asaph). We connect names including nant (stream), blaen (source of a stream), glan (bank), rhyd (ford), ffynnon (well) with rivers, but the most common element in this context is aber.

Aber (estuary) means either a place where a river flows to the sea, or where a smaller river flows into a larger river. The river Daron flows to the sea at Aberdaron, for example, and Aberhonddu (Brecon) describes the place where the river Honddu joins the river Usk.:: snip

Common useage all over Wales is Glan yr Afon. Also in Cheshire, wide area of flowing river or canal is FLASH. Cheshire seem to make use of word mutations e.g. Oller Bank Benk, Benk also used for raised area, not necces. river bank (Clinkerbenk). Must root out tome "Origins of Anglo Saxon placenames".