Afon Honddu (Monmouthshire)

The River Honddu (Welsh: Afon Honddu) (pronounced hon-thee) is a river in the Black Mountains within the Brecon Beacons National Park, southeast Wales. Early recorded versions of the name are of the form Hothenei and hodni which are believed to contain the adjective 'hawdd' meaning for example, pleasant or easy. Later forms such as Honddye have undergone metathesis whereby -ddn- became -ndd-.

It rises within the county of Powys near the Gospel Pass at the head of the Vale of Ewyas down which it flows, passing southwards into Monmouthshire to Llanvihangel Crucorney before turning northeastwards to join the River Monnow at the point on the Wales-England border where that river too makes a sudden change of direction. The only significant tributary to join the Honddu is the Nant Bwch though numerous smaller streams flow down the steep sides of the Vale of Ewyas to add to the river's flow.

It is likely that the Honddu continued on a southerly course beyond Llanvihangel Crucorney prior to the last ice age but has since been diverted by the presence of a large terminal moraine which stretches impressively across the valley to the west of the village. The southwest to northeast alignment of both the Honddu and the Monnow appear to be related to the course of the Neath Disturbance, an ancient geological weakness, which runs through the valley to the north of the Sugarloaf and on towards Hereford.

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