Mapping Mountains – Significant Height Revisions – 100m Twmpau and Y Trechol – The Dominant Hills of Wales

 

Morris’ Meadow (SN 019 183) 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.                            

LIDAR image of Morris' Meadow (SN 019 183)

The criteria for the two listings 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

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Morris’ Meadow and this was derived from the Tithe map, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the B4329 road farther to its west and the A40 road farther to its south, and has the town of Hwlffordd (Haverfordwest) towards the west south-west.

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 122m, based on the spot height positioned at SN 02261 18187 which appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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 Morris Meadow (SN 019 183)

The summit height produced by LIDAR analysis is 119.4m positioned at SN 01923 18373, and this 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 119.4m and this was derived from LIDAR analysis, this is 2.6m lower than the originally listed summit height of 122m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Morris’ Meadow 

OS 1:50,000 map:  157, 158

Summit Height (New Height):  119.4m (LIDAR) 

Summit Grid Reference:  SN 01923 18373 (LIDAR) 

Bwlch Height:  65.2m (LIDAR) 

Bwlch Grid Reference:  SN 01619 20933 (LIDAR) 

Drop:  54.2m (LIDAR) 

Dominance:  45.41% (LIDAR) 

 

Myrddyn Phillips (May 2023)