Wednesday, 25 March 2020

Mapping Mountains – Hill Reclassifications – Y Pedwarau – The 400m Hills of Wales

Pt. 402.3m (SN 964 370) – 400m Sub-Pedwar deletion

There has been a deletion to the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Aled Williams.

LIDAR image of Pt. 402.3m (SN 964 370)

The criteria for the list that this deletion applies to are:

Y PedwarauThe 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being deleted from the 400m Sub-Pedwar category.  The criteria for 400m Sub-Pedwar status 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.

The hill is being listed by the point (Pt. 402.3m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the authors, and it is adjoined to the Mynydd Epynt group of hills, which are situated in the south-eastern part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the A40 road to its south and the B4520 road to its east, and has the hamlet of Merthyr Cynog towards the east.

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

When the 1st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was listed as a 400m Sub-Pedwar with 20m of drop, based on the 403m summit height that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map and the 383m bwlch height that appeared as a spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage map.  The 383m bwlch spot height is also shown on Ordnance Survey data that appears on the Magic Maps website. 

Extract from the Magic Maps website

The details for this hill were re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This re-assessment enabled the position of the 383m bwlch spot height to be compared to the positioning of the 5m bwlch contouring, resulting in the drop value for this hill provisionally decreasing to an estimated c 16m based on an estimated bwlch height of c 387m.

Extract from OS Maps

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.

Therefore, the deletion of this hill from 400m Sub-Pedwar status is due to LIDAR analysis, resulting in a 402.3m summit height and a 385.4m bwlch height, with these values giving this hill 16.8m of drop, which is insufficient for 400m Sub-Pedwar status.

The full details for the hill are:

Group:  Mynydd Epynt 

Name:  Pt. 402.3m

OS 1:50,000 map:  160

Summit Height:  402.3m (LIDAR)

Summit Grid Reference:  SN 96417 37069 (LIDAR)

Bwlch Height:  385.4m (LIDAR)

Bwlch Grid Reference:  SN 95979 37133 (LIDAR)

Drop:  16.8m (LIDAR)

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

Aled Williams and Myrddyn Phillips (March 2020)

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