Monday, 29 February 2016

Mapping Mountains – Significant Height Revisions – Y Pedwarau


Cwm Cynydd Bank (SO 061 726)

This is the twenty sixth post under the heading of Significant Height Revisions, and the Trimble survey that resulted in this height revision was conducted on 18th February 2016.

The resulting significant height revision was conducted in the hills of the Pegwn Mawr range in mid Wales, during a walk taking in one 300m Twmpau and three Pedwarau, with some of these hills immersed in part of the conifer plantation that takes in land to the north of Abaty Cwm Hir (Abbey Cwmhir).

The hill is situated in this 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 and situated 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.

The name of the hill is Cwm Cynydd Bank and prior to the Trimble survey it was listed as a Pedwar with its summit height of 450m taken from the Ordnance Survey 1:50,000 map.  This height equates to the old imperial height of 1,477ft that is given 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 accuracy level of the Trimble to attain its 0.1m 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 at least 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 current Ordnance Survey 1:25,000 maps.



The full details for the hill are:


Cardinal Hill:  Brondre-fawr Hill

Summit Height:  454.9m (converted to OSGM15)

Name:  Cwm Cynydd Bank

OS 1:50,000 map:  136, 147

Summit Grid Reference:  SO 061 726

Drop:  83.9m (converted to OSGM15)


Gathering data from the summit of Cwm Cynydd Bank (SO 061 727)

For details on the survey of this hill please click {here}


Myrddyn Phillips and Aled Williams (February 2016)



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