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

Mynydd Carrog (SH 774 462) – 400m Sub-Pedwar addition

There has been an addition to the listing of Y Pedwarau - The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill initially derived from analysis of data on the Ordnance Survey 1:25,000 Explorer map, coupled with the 5m contouring on the OS Maps website, and with confirmation via subsequent LIDAR analysis conducted by Myrddyn Phillips.

Llyn Conwy from Mynydd Carrog (SH 774 462)

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

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

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Mynydd Carrog, and this was derived from historical information with research conducted by Aled Williams, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region C1, Sub-Region C1A), and it is positioned with a minor road to its west and the B4407 road to its south-east and has Llyn Conwy to its east and the village of Penmachno towards the north north-east.

Prior to analysis of data on OS Maps this hill was listed with an estimated c 19m of drop, based on the 486m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 467m bwlch height, based on interpolation of bwlch contouring between 460m – 470m.

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

The details for this hill were re-assessed when the Ordnance Survey non-contour Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping has many spot heights not on other publicly available Ordnance Survey maps.  After re-assessment the listed details for this hill remained the same.

One of the resources recently available online is the interactive mapping hosted on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  This is the replacement for OS Get-a-map and has 5m contour intervals, which has enabled the height of the bwlch to be narrowed down when compared to the 10m contour intervals on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  Therefore, with a 486m summit spot height on the Ordnance Survey 1:25,000 Explorer map and an estimated c 466m bwlch height , based on contouring between 465m – 470m, this hill is now listed with an estimated c 20m of drop.

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.

LIDAR image of Mynydd Carrog (SH 774 462)

Therefore, the confirmation of the addition of this hill to 400m Sub-Pedwar status is due to LIDAR analysis, resulting in a 486.45m summit height and a 464.7m bwlch height, with these values giving this hill 21.7m of drop, which is sufficient for it to be classified as a 400m Sub-Pedwar.

 

Group:  Arenig Fach

 

Name:  Mynydd Carrog

OS 1:50,000 map:  125

Summit Height:  486.45m (LIDAR)

Summit Grid Reference:  SH 77472 46279 (LIDAR)

Bwlch Height:  464.7m (LIDAR)

Bwlch Grid Reference:  SH 77586 46736 & SH 77590 46734 (LIDAR)

Drop:  21.7m

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:

Y Pedwarau

Y Pedwarau – 400m Sub-Pedwarau

Y Pedwarau – 390m Sub-Pedwarau

Y Pedwarau – 390m Double Sub-Pedwarau

Myrddyn Phillips and Aled Williams (July 2018)