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

Gelli Hir (SN 999 883) – Lesser Dominant addition

There has been an addition to the listing of Y Trechol – The Dominant Hills of Wales with the summit height confirmed by a survey with the Trimble GeoXH 6000 and later substantiated by a survey with the Leica GS15, and the bwlch height later ascertained from LIDAR analysis conducted by Myrccyn Phillips, resulting in this hill being added to the Lesser  Dominant list. 

The criteria for this listing are:

Y Trechol – The Dominant Hills of Wales - Welsh P30s whose prominence equal or exceed half that of their absolute height, with the criteria for Lesser Dominant status being those additional Welsh P30s whose prominence is 33% or more and below 50% of their absolute height.

The details relating to this hill’s addition to the Lesser Dominant list are retrospective as the confirmation was dependent upon a survey with the Trimble GeoXH 6000 which was conducted by Myrddyn Phillips on the 7^th February 2014, the result was later substantiated by a survey with the Leica GS15 which was conducted by John Barnard, Graham Jackson and Myrddyn Phillips on the 2^nd May 2014.

Prior to the survey with the Trimble GeoXH 6000 this hill’s twin 308m map heighted summit of Y Gaer which is positioned at SO 01350 87380 was prioritised as being listed as a Lesser Dominant.  The survey with the Trimble separated these twin map heighted tops and resulted in the deletion of Y Gaer, and the addition of Gelli Hir to Lesser Dominant status.

The name of the hill is Gelli Hir and it is adjoined to the Pumlumon range of hills which are situated in Mid and West Wales (Region B, Sub-Region B2).  The hill has the A 470 road and the Afon Hafren (River Severn) to its east, and is positioned between the small community of Caersws to the north-east and the town of Llanidloes towards the south-west. 

As the summit of the hill is not on designated open access land permission to visit should be sought, however as a public footpath traverses this hill’s elongated and broad summit ridge in a north – south direction and passes close to the high point of the hill, common sense should prevail as a diversion to the summit is only a short distance away.

The addition of Gelli Hir to Lesser Dominant status was confirmed by a survey with the Trimble GeoXH 6000 and then substantiated by a survey with the Leica GS15, resulting in a summit height of 307.2m (converted to OSGM15) which is 0.1m higher than its twin map heighted summit of Y Gaer (SO 013 873), with LIDAR analysis giving the height of the bwlch as 182.5m, resulting in 124.7m of drop and 40.60% dominance this hill is added to the Lesser Dominant list.

The full details for the hill are:

Group:  Pumlumon

Name:  Gelli Hir

Dominance:  40.60% (Leica GS15 summit and LIDAR bwlch)

OS 1:50,000 map:  136

Summit Grid Reference:  SN 99903 88383 (Leica GS15)

Summit Height:  307.2m (converted to OSGM 15, Leica GS15)

Drop Summit to Bwlch:  124.7m (Leica GS15 summit and LIDAR bwlch)

Drop Bwlch to ODN:  182.5m (LIDAR) 

Gelli Hir (SN 999 883) is now added to the ranks of Lesser Dominant hills

For details on the survey that resulted in the addition of this hill to Lesser Dominant status

Myrddyn Phillips (December 2017)