Mapping Mountains – Significant Height Revisions – Y Pellennig, 30-99m Twmpau and Y Trechol - The Dominant Hills of Wales

Emsger (SM 651 226)

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig, 30-99m Twmpau and Y Trechol - The Dominant Hills of Wales, with the summit height and its location, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Emsger (SM 651 226)

The criteria for the three listings that this height revision affects are:

Y Pellennig –The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on Mapping Mountains to download in Google Doc format. 

Y Pellennig - The Remotest Hills of Wales by Myrddyn Phillips and Aled Williams

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

30-99m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.  

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Emsger, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned on an island with a minor road over 7.00km to its east, and has the small city of Tyddewi (St David's) towards the east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a summit height of 37m, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

However, it was not until the survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed.  With the caveat that the island is predominantly rock and if not for a series of steps leading up toward its summit its ascent would no doubt prove more problematic.  The upper part of Emsger has a lighthouse on it; this was built in 1839, and was converted to operating by electric in 1959, and demanned and automated in 1983.  Adjacent to the lighthouse are buildings and platforms, and therefore what once constituted the natural summit of the island is either buried under the lighthouse/platforms or it was destroyed during construction of the lighthouse.

The Trimble GeoXH 6000 gathering data 0.99m above the highest remaining natural ground at the summit of Emsger, otherwise known as South Bishop (SM 651 226) which resulted in this island's significant height revision

The summit height produced by the Trimble GeoXH 6000 survey is 33.8m and is positioned at SM 65116 22619, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 33.8m and this was derived from a Trimble GeoXH 6000 survey, this is 3.2m lower than the previously listed summit height which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Garn Fawr

Name:  Emsger

OS 1:50,000 map:  157

Summit Height (New Height):  33.8m (converted to OSGM15)

Summit Grid Reference:  SM 65116 22619

Bwlch Height:  N/A (island)

Bwlch Grid Reference:  N/A (island)

Drop:  33.8m

Dominance:  100.00%

Remoteness:  7.725km

Myrddyn Phillips and Aled Williams (June 2016)