Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Pt. 70.3m (SH 309 297) – Lesser Dominant deletion

There has been a deletion to the listing of Y Trechol – The Dominant Hills of Wales due to analysis of data produced by LIDAR and which was initially conducted by Chris Crocker, and subsequently by Myrddyn Phillips, with the details relating to this hill taken from the latter’s analysis.

The criteria for inclusion to the Dominant list are all Welsh P30 hills whose prominence equal or exceed half that of their absolute height, whilst the criteria for the Lesser Dominant list are those additional Welsh P30s whose prominence is 33% or more and below 50% of their absolute height.

Prior to analysis of data produced via LIDAR this hill was listed with 42.25% Dominance based on an estimated summit height of c 71 and the 41m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website, with these values giving this hill c 30m of drop.

As the author does not know a local or historical name for this hill it is being listed by the point (Pt. 70.3m) notation, and it is positioned in the Pen Llŷn group and placed in the North Wales region (Region A, Sub-Region A1), and is situated between the small communities of Llanbedrog to the north-east, Mynytho to the north-west and Abersoch to the south.

If wanting to visit the hill permission to do so should be sought as the summit area is not a part of designated open access land, however the hill has a number of public footpaths encircling it that start from the A 499 road to its east and the network of minor roads to its north and west.

The deletion of Pt. 70.3m from Lesser Dominant status is due to analysis of data produced by LIDAR initially conducted by Chris Crocker, and subsequently by Myrddyn Phillips, with the details from the latter’s analysis being presented below.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The analysis of data produced via LIDAR gives the hill the following details:

Pt. 70.3m

Summit Height:  70.3m

Summit Grid Reference:  SH 30993 29739

Bwlch Height:  40.7m

Bwlch Grid Reference:  SH 31021 30355

Drop:  29.6m

Dominance:  not applicable

Therefore, the 70.267m data produced via LIDAR for the summit position at SH 30993 29739 and the 40.710m data produced via LIDAR for the bwlch position at SH 31021 30355 gives this hill 29.557m of drop, with the drop value insufficient for qualification to the Dominant list.

The full details for the hill are:

Group:  Pen Llŷn

Name:  Pt. 70.3m

Dominance:  not applicable

OS 1:50,000 map:  123

Summit Grid Reference:  SH 30993 29739 

Summit Height:  70.3m (data via LIDAR)

Drop Summit to Bwlch:  29.6m (data via LIDAR)

Drop Bwlch to ODN:  40.7m (data via LIDAR)

My thanks to Chris Crocker for initial LIDAR analysis and bringing the details of this hill to my attention

Myrddyn Phillips (April 2018)