Mapping Mountains – Summit Relocations – Y Pedwarau - The 400m Hills of Wales

Y Drum (SH 735 428)

There has been a Summit Relocation to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips initiated by an on-site inspection conducted by Aled Williams.

Y Drum (SH 735 428)

The criteria for the list that this summit relocation applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills; 500m Sub-Pedwarau, 500m Double Sub-Pedwarau, 400m Sub-Pedwarau, 390m Sub-Pedwarau and the 390m Double Sub-Pedwarau.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Y Drum, and this was derived from local and historical information with research conducted by Aled Williams, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region C1, Sub-Region C1A), and it is positioned with the B4391 road to its south and the B4407 road to its east, and has the village of Ffestiniog towards the west south-west.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 479m summit height positioned at SH 733 428, with the caveat that the four small 480m ring contours just to the north-east and east had been missed.

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

After the sub list was standardised and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 35m of drop, based on an estimated c 482m summit height and an estimated c 447m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013 the details for this hill were re-evaluated and it was listed with a 486m summit height, based on the spot height that appears on the Harvey 1:40,000 British Mountain Map to Eryri/Snowdonia and which is positioned in the vicinity of the most northerly of the 480m ring contours that appear on the Ordnance Survey 1:25,000 Explorer map, with the high point of this contour ring positioned at SH 73542 42903.

Extract from the Harvey 1:40,000 British Mountain Map to Eryri/Snowdonia

The position of the listed summit of this hill was subsequently moved to SH 73541 42812 after an on-site inspection by Aled Williams.  However, it was not until the survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed.

The new summit position of Y Drum is highlighted in yellow, with the old position of the summit highlighted in red.  Photo:  Aled Williams

This summit relocation was later confirmed by the Trimble GeoXH 6000 with the highest ground on this hill surveyed as 483.574m positioned at SH 73541 42812, whilst the position of the 486m Harvey spot height at SH 73542 42903 was surveyed as 482.686m, and this comes within the parameters of the Summit Relocations  used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

The Trimble GeoXH 6000 gathering data at the new summit position of Y Drum (SH 735 428)

The position of the ten figure grid reference determined by the Trimble GeoXH 6000 for the four 480m contour rings that appear on the contemporary Ordnance Survey 1:25,000 map and their respective heights appear below:

Contour 1:  SH 73542 42903    482.686m

Contour 2:  SH 73563 42818    482.965m

Contour 3:  SH 73541 42812    483.574m

Contour 4:  SH 73475 42798    480.924m

Contour 1 is the largest and is where the 486m Harvey Maps spot height appears, Contour 4 is the smallest and Contours 2 and 3 are placed near to one another.  It is Contour 3 at SH 73537 42813 that is noticeably higher from every position, and this was confirmed by the Trimble GeoXH 6000 survey.

Therefore, the height produced by the Trimble GeoXH 6000 survey to the summit of this hill is 483.6m and is positioned at SH 73541 42812.  This position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 106 metres southward from the previously listed summit position which was based on the 486m spot height that appears on the Harvey 1:40,000 British Mountain Map to Eryri/Snowdonia.

The full details for the hill are:

Group:  Arenig Fach 

Name:  Y Drum

OS 1:50,000 map:  124

Summit Height:  483.6m (converted to OSGM15) 

Summit Grid Reference (New Position):  SH 73541 42812 

Bwlch Height:  449.2m (converted to OSGM15) 

Bwlch Grid Reference:  SH 73778 42825

Drop:  34.4m

Aled Williams and Myrddyn Phillips (July 2015 and March 2016)