Mapping Mountains – Summit Relocations – 30-99m Twmpau

Bryn y Bont (SH 596 459)

There has been a Summit Relocation to a hill that now appears in the Double Sub-Twmpau list that accompanies the 30-99m Twmpau list, with the hill’s height and drop confirmed by analysis by Aled Williams of data produced by LIDAR.  With the title of Twmpau being an acronym for thirty welsh metre prominences and upward.

Accompanying each 100m height band within the main Twmpau list is a sub list entitled the Sub-Twmpau, with the Double Sub-Twmpau attached to the lower tier height band of Welsh hills.

The criteria for the lower tier of Twmpau hills are:

30-99m Twmpau – All Welsh hills at and above 30m and below 100m in height with 30m minimum drop.

30-99m Sub-Twmpau – All Welsh hills at and above 30m and below 100m in height with 20m or more and below 30m of drop.

Double Sub-Twmpau – All Welsh hills at and above 20m and below 30m in height with 20m or more and below 30m of drop.

The name of the hill is Bryn y Bont and it is situated in the Moelwynion range of hills and is placed in the Region of North Wales (Region A, Sub-Region A1).  The hill is positioned with the A 4085 road to its north and its east and the A 498 road to its west, and has the Afon Glaslyn also to its immediate west, with the hamlet of Nantmor positioned to the east of the hill and the village of Beddgelert towards its north.

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so an ascent from the convenience of the road to its north or east is likely to be the easiest.

Prior to analysis of data produced via LIDAR this hill was not listed in the Hills to be surveyed sub list that accompanied the Welsh P30 lists published on Geoff Crowder’s v-g.me website.  When these lists were re-evaluated after they were standardised and also drop values added, this hill was listed with c 16m of drop based on an estimated c 20m summit height positioned at SH 59600 46035 which was based on this hill’s small uppermost 20m ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and an estimated bwlch height of c 4m based on bwlch contouring at 10m intervals and between 0 – 10m, with the caveat that the 4m spot height positioned at SH 59756 45814 and shown on the Ordnance Survey 1:25,000 Explorer map is probably not at the position of the critical bwlch.  However, since these lists were re-evaluated OS Maps (the recent replacement for OS Get-a-map) are now available and show 5m contour intervals with an uppermost 25m ring contour for this hill. 

Extract from the Ordnance Survey 1:25,000 Explorer map

Extract from the Ordnance Survey Interactive Coverage map hosted on the Geograph website indicating the position of the LIDAR summit in relation to the uppermost 20m ring contour

The uppermost 25m ring contour shown on the OS Maps website

The summit height produced by data via LIDAR is 25.2m and is positioned at SH 59641 45973, this position is not given a spot height on Ordnance Survey maps and is outside of the uppermost 20m ring contour on the 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 70 metres south-eastward from the previously listed summit position.

The full details for the hill are:

Group:  Moelwynion

Summit Height:  25.2m (data via LIDAR)

Name:  Bryn y Bont

OS 1:50,000 map:  115

Summit Grid Reference (New Position):  SH 59641 45973  

 

Drop:  20.9m (data via LIDAR)

My thanks to Aled Williams for sending the details of this hill to me

Myrddyn Phillips (February 2018)