Mapping Mountains – Significant Height Revisions – 100m Twmpau

 

Coed Uchaf (SJ 232 683) 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by JoeNuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Coed Uchaf (SJ 232 683)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Coed Uchaf, and it is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned encircled by minor roads, with the A55 road farther to its north, the B5123 road farther to its west, the A541 road farther to its south and the A5119 road farther to its east, and has the town of Y Fflint (Flint) towards the north.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of c 160m positioned at SJ 232 686, based on the uppermost non-interpolated ring contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated against the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 162m summit spot height positioned at SJ 23209 68591.

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 summit image of Coed Uchaf (SJ 232 683)

The height produced by LIDAR analysis to the summit of this hill is 161.7m positioned at SJ 23205 68344 as opposed to the 160.5m LIDAR height positioned at SJ 23205 68597.  This relocated summit position is not given an uppermost 160m ring contour on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and this height 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 or Harvey 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 to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 161.7m and this was derived from LIDAR analysis, this is 1.7m higher than the originally listed summit height of a non-interpolated c 160m and 0.3m lower than the 162m spot height that was positioned at SJ 23209 68591 on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Moel y Gamelin 

Name:  Coed Uchaf 

OS 1:50,000 map:  117

Summit Height (New Height):  161.7m (LIDAR) 

Summit Grid Reference:  SJ 23205 68344 (LIDAR) 

Bwlch Height:  132.6m (LIDAR) 

Bwlch Grid Reference:  SJ 23101 68383 (LIDAR) 

Drop:  29.1m (LIDAR) 

 

Myrddyn Phillips (January 2024)