Mapping Mountains – Hill Reclassifications – Y Pedwarau

Y Gribin (SH 902 172) – Pedwar reclassified to 400m Sub-Pedwar

There has been a reclassification to the listing of Y Pedwarau due to LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips, coupled with analysis of contemporary Ordnance Survey maps, including the 5m contouring on the OS Maps website, and Ordnance Survey data on the WalkLakes website.

LIDAR image of Y Gribin (SH 902 172)

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

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height with 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being reclassified to 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 name of the hill is Y Gribin, and it is adjoined to the Y Berwyn group of hills, which are situated in the eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with a minor road and the Afon Dyfi (River Dovey) to its west, and has the small community of Llanymawddwy towards the north.

This and its adjoining hill towards the north (which is also listed by the same name of Y Gribin) are both given a 485m summit spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and prior to this reclassification it was the southerly of these two hills (SH 902 172) that was prioritised for Pedwar status, whilst the northerly hill (SH 906 175) was listed as the 400m Sub-Pedwar.

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. 

The summit height produced by LIDAR analysis for the southerly of these two hills is 484.8m and is positioned at SH 90233 17288; however there is no LIDAR coverage for the northerly summit or the bylchau adjoined to each hill.

LIDAR summit image of Y Gribin (SH 902 172)

The details for these two hills were then re-examined with contouring on the OS Maps website, this is the replacement for OS Get-a-map and has contours at 5m intervals.  The details for each hill were also examined via Ordnance Survey data on the WalkLakes website.  Lastly online logs that appear on the Hill Bagging website were consulted.  The data for each summit is given below:

Y Gribin

Ordnance Survey spot height:  485m (SH 902 172)

LIDAR: 484.8m summit at SH 90233 17288

OS Maps:  480m uppermost contour

WalkLakes spot height:  484m

Y Gribin

Ordnance Survey spot height:  485m (SH 906 175)

LIDAR:  not covered

OS Maps:  485m uppermost contour

WalkLakes website:  480m uppermost contour

There are two online logs of note on the Hill Bagging website, these have been posted by Anton Ciritus and Mick Moore and both make reference that in their view the northerly of these two summits is the higher.

Extract from the OS Maps website

Therefore, as evidence supports the northerly of the two Y Gribin summits to be the higher, the southerly summit is reclassified from the Pedwar to the 400m Sub-Pedwar.

Extract from the WalkLakes website

The reclassification of Y Gribin (SH 902 172) from Pedwar to 400m Sub-Pedwar status is due to a combination of factors, including LIDAR analysis, analysis of data on the OS Maps website and the WalkLakes website and online logs on the Hill Bagging website.  Therefore, with a 484.8m summit height ascertained from LIDAR analysis and an estimated bwlch height of c 462m taken from interpolation of 5m contouring on the OS Maps website, these values give this hill c 23m of drop, which qualifies it for 400m Sub-Pedwar status.

The full details for the hill are:

Group:  Y Berwyn

 

Name:  Y Gribin

OS 1:50,000 map:  125

Summit Height:  484.8m (LIDAR)

Summit Grid Reference:  SH 90233 17288 (LIDAR)

Bwlch Height:  c 462m (interpolation)

Bwlch Grid Reference:  SH 90496 17361 (interpolation)

Drop:  c 23m

For the additions, reclassifications and deletions to Y Pedwarau 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 (October 2019)