Mapping Mountains – Summit Relocations – 200m Twmpau

Gwastadedd (SN 629 594) 

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, 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 Gwastadedd (SN 629 594)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Gwastadedd and this was derived from the Tithe map, and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-west, the B4342 road to its south-west and the B4578 road to its east, and has the town of Tregaron towards the east. 

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

When the original 200m 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 220m based on the uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map which is positioned at SN 633 592, with an accompanying note stating; Two points of same height – other at SN 630594. 

The first LIDAR summit image of Gwastadedd

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. 

The second LIDAR summit image of Gwastadedd

LIDAR analysis gives the highest ground on this hill as 222.2m positioned at SN 62925 59399.  However, this is a part of a raised field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

The third LIDAR summit image of Gwastadedd

The height produced by LIDAR analysis to the natural summit of this hill is 222.1m positioned at SN 62929 59415, and this position in relation to the raised field boundary comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to when the high point of the hill is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit 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 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.

Therefore, the summit height produced by LIDAR analysis is 222.1m and this is to the natural summit of the hill which is positioned at SN 62929 59415, 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 16 metres northward from where the high point of the raised field boundary is positioned. 

 

The full details for the hill are:

Group:  Mynydd Bach 

Name:  Gwastadedd 

OS 1:50,000 map:  146

Summit Height:  222.1m (LIDAR) 

Summit Grid Reference (New Position):  SN 62929 59415 (LIDAR) 

Bwlch Height:  185.9m (LIDAR) 

Bwlch Grid Reference:  SN 63680 59433 (LIDAR) 

Drop:  36.2m (LIDAR)

 

Myrddyn Phillips (November 2022)