Mapping Mountains – Significant Height Revisions – 100m Twmpau

 

Beddau (SO 185 977) 

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 confirmed by LIDAR analysis conducted by Myrddyn Phillips. 

Beddau (SO 185 977)

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 with 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 listed by is Beddau, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with the A483 road to its north-west, a minor road to its south-east and the B4386 road farther to its south-east, and has the village of Aberriw (Berriew) 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 included in the main P30 list with a c 120m summit height taken from the uppermost contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

When the accompanying sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with c 36m of drop, based on an estimated c 124m summit height and an estimated c 88m bwlch height, based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

Since the original compilation of this list there have been a number of Ordnance Survey 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 are current and digitally updated such as the mapping on the WalkLakes website and the Magic Maps website. 

One of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data.  This map has many spot heights not on other publicly available Ordnance Survey maps and for this hill a 126m spot height is given on the area of its summit. 

Extract from the Magic Maps website

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 Beddau (SO 185 977)

The summit height produced by LIDAR analysis is 126.0m positioned at SO 18549 97771, this is not a substantial height revision compared to some revised heights but it does come 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 summit 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. 

The summit of Beddau

Therefore, this hill’s new listed summit height is 126.0m and this was derived from LIDAR analysis, this is 2.0m higher than the previously listed and estimated summit height of c 124m which was based on interpolation of the hill’s uppermost 120m ring contour on the Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Carnedd Wen

Name:  Beddau

OS 1:50,000 map:  136

Summit Height (New Height):  126.0m (LIDAR)

Summit Grid Reference:  SO 18549 97771 (LIDAR)

Bwlch Height:  87.9m (LIDAR)

Bwlch Grid Reference:  SO 18841 98344 (LIDAR)

Drop:  38.1m (LIDAR)

 

Myrddyn Phillips (March 2021)