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

Mynydd Bryn Du (SH 937 523)

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 LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Mynydd Bryn Du (SH 937 523)

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

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, with this hill being included in the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  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 Mynydd Bryn Du, and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region C1, Sub-Region C1A), and it is positioned with the A543 road to its north-west, the A5 road to its south and the B4501 road to its east, and has the village of Cerrigydrudion towards the south south-east.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it did not meet the criteria then used in this sub category. 

When 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 a 478m summit height based on the spot height positioned at SH 93208 52640 that appears on the Ordnance Survey 1:25,000 Explorer map.  This is also the height and position that the summit of the hill was listed in the 1^st edition of the Y Pedwarau published by Europeaklist in May 2013.  However, toward the south-east of this position is another large 470m ring contour that did not possess a spot height on any publicly available map of the time.

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

Since publication of the 1^st edition of the Y Pedwarau there are a number of Ordnance Survey maps now available online, one is the non-contour Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.  This map is the recent replacement for a contoured map that had many spot heights not on any other publicly available Ordnance Survey map.  Importantly for this hill the recently available non-contour map shows a 480m spot height where the previously non-spot heighted 470m ring contour is positioned.

Extract from the Ordnance Survey non-contour Vector Map Local hosted on the Geograph website

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and shows a 479m spot height close to where the 480m spot height appears on the non-contour Vector Map Local.

Extract from the interactive mapping hosted on the WalkLakes website

Another resource now available online is the interactive mapping hosted on the Welsh Government website and entitled the DataMapWales.  This mapping has 5m contours and its detail matches that produced from the OS Terrain 5 product, which compliments much of that produced from LIDAR.  And for the summit area of this hill, two uppermost 475m ring contours are shown with the westerly given a 480m spot height.

Extract from the DataMapWales

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR image of Mynydd Bryn Du showing the originally listed summit position (top left) and the previously listed summit position (left one lower right) and the new listed summit position (right one lower right)

LIDAR analysis gives the highest ground on this hill as 480.0m positioned at SH 93714 52345, with LIDAR giving 479.0m positioned at SH 93210 52641 for the originally listed summit position and 479.9m positioned at SH 93644 52319 for the previously listed summit position, 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 listing of a new twin summit or 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.

LIDAR summit image of Mynydd Bryn Du showing the previous summit position (SH 93644 52319)on the left and the new summit position (SH 93714 52345) on the right

Therefore, the height produced by LIDAR analysis to the summit of this hill is 480.0m and is positioned at SH 93714 52345.  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 500 metres south-eastward from the position of the 478m map spot height which was the original summit position and approximately 70 metres east north-eastward from the position of the 480m spot height and the previously listed summit position.

The full details for the hill are:

Group:  Mynydd Hiraethog

Name:  Mynydd Bryn Du

OS 1:50,000 map:  116

Summit Height:  480.0m (LIDAR)

Summit Grid Reference (New Position):  SH 93714 52345 (LIDAR)

Bwlch Height:  456.1m (LIDAR)

 

Bwlch Grid Reference:  SH 92952 52912 (LIDAR)

         

Drop:  23.9m (LIDAR)

Myrddyn Phillips and Aled Williams (November 2019)