Mapping Mountains – Significant Height Revisions – Y Pedwarau

Cwm Cynnydd Bank (SO 061 726)

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau that was initiated by a survey with the Trimble GeoXH 6000, with the survey that resulted in this height revision being conducted on 18^th February 2016.  The criteria for Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.

The name of the hill is Cwm Cynnydd Bank and it is situated in the hills of the Pegwn Mawr range which is positioned in mid Wales and the survey was conducted during a walk taking in one Trichant and three Pedwar hills.

The hill is situated in woodland, but can be accessed from open hillside and forest tracks to within a few metres of its summit, which is positioned in mature conifer plantation just to the north of a broad path.  The hill is situated to the north of the small community of Abaty Cwm Hir (Abbey Cwmhir) and to the south-east of the small community of Bwlch y Sarnau.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed as a Pedwar with a 450m summit height taken the spot height that appears on the Ordnance Survey 1:50,000 Landranger map.  This height equates to the old imperial height of 1,477ft that appears on the Ordnance Survey 1:25,000 Historical Map which originates from the series of Ordnance Survey old Six-Inch maps.  This height appears near to or on the broad path that gives access to this hill’s summit and which traverses its broad north-east to south-west ridge.

When surveying this summit I waited a long time for the Trimble GeoXH 6000 to attain its 0.1m accuracy level before data should be logged, during this time I assessed the lay of land around the summit and tried to keep warm.  I estimated the summit of the hill to be approximately 3m higher than the path where the centralised imperial height appears on the old Six-Inch map. 

Therefore this hill’s new summit height is 454.9m (converted to OSGM15) which is 4.9m higher than its previously listed height of 450m and 14.9m higher than the uppermost 440m ring contour that appears on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill:  Brondre-fawr Hill

Summit Height:  454.9m (converted to OSGM15)

Name:  Cwm Cynnydd Bank

OS 1:50,000 map:  136, 147

Summit Grid Reference:  SO 06116 72668

Drop:  83.9m (converted to OSGM15)

Gathering data at the summit of Cwm Cynnydd Bank (SO 061 727) which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (February 2016)