Sunday, 16 April 2017

Mapping Mountains – Hill Reclassifications – Yr Uchafion

Blaen yr Henbant (SO 254 217) - Double Sub-Uchaf addition

There has been an addition to the listing of Yr Uchafion instigated from analysis of LIDAR data by Aled Williams.  Yr Uchafion is the draft title for a list of the Welsh 500m P15s that takes in all hills in Wales at or above 500m that have a minimum drop of 15m, the list is a joint compilation with Aled Williams, and details relating to this list were published on the Mapping Mountains site in November 2015.

Accompanying the main Yr Uchafion list are three sub lists; 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub-Uchaf categories, with the addition of this hill affecting the Double Sub-Uchaf classification, with the criteria for inclusion to this sub category being all Welsh hills at or above 490m and below 500m in height that have 14m or more and below 15m of drop.

Prior to analysis of LIDAR data the hill was catalogued with 12m of drop based on the 498m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and the 486m bwlch spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The hill is situated in the Mynyddoedd Duon (Black Mountains) group of hills with its Cardinal Hill being Waun Fach (SO 215 299) and is placed in the Region of South Wales (Region C, Sub-Region C3), and is positioned between the town of Crucywel (Crickhowell) to the south-west and the small community of Forest Coal Pit to the east south-east.

The hill can be accessed via a bridleway from its south-west that forms a part of the Beacons Way, or from public footpaths towards the south and north-east.  However, the hill is positioned at the end of one of this hill ranges extended ridges and a two car walk taking in the full length of this ridge ending on the summit of Blaen yr Henbant is highly recommended.

The name of the hill is Blaen yr Henbant and its inclusion as a Double Sub-Uchaf is due to the analysis of LIDAR data by Aled Williams.  LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

Aled’s analysis of LIDAR data gives the hill the following details:

Blaen yr Henbant

Summit Height:  497.8m (converted to OSGM15)

Summit Grid Reference:  SO 25412 21736

Bwlch Height:  483.0m (converted to OSGM15)

Bwlch Grid Reference:  SO 25537 22004

Drop:  14.8m

Therefore, the 497.8m (converted to OSGM15) LIDAR data produced for the summit position at SO 25412 21736 and the 483.0m (converted to OSGM15) LIDAR data produced for the bwlch position at SO 25537 22004 gives this hill 14.8m of drop and when combined with its summit height is sufficient for the hill to be included as a Double Sub-Uchaf.

The full details for the hill are:

Cardinal Hill:  Waun Fach

Summit Height:  497.8m (converted to OSGM15) (LIDAR data)

Name:  Blaen yr Henbant

OS 1:50,000 map:  161

Summit Grid Reference:  SO 25412 21736
Drop:  14.8m (converted to OSGM15) (LIDAR data)

The overall total for Yr Uchafion / The Welsh 500m P15s remains at 631 hills with the total for the Double Sub-Uchaf category now being 6.

For the additions, reclassifications and deletions to Yr Uchafion / The Welsh 500m P15s reported on Mapping Mountains please consult the following Change Registers:

Myrddyn Phillips and Aled Williams (April 2017)

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