Saturday, 12 May 2018

Mapping Mountains – Hill Reclassifications – Y Pedwarau

Mynydd Ty’n y Fach (SH 687 097) – 400m Sub-Pedwar deletion

There has been a deletion to the listing of Y Pedwarau due to LIDAR analysis conducted by Myrddyn Phillips and subsequently confirmed via a survey with the Trimbe GeoXH 6000.  Y Pedwarau is the title for the list of 400m hills of Wales and takes in all Welsh hills at or above 400m and below 500m in height that have a minimum 30m of drop, the list is a joint compilation between Myrddyn Phillips and Aled Williams and it commenced publication on Mapping Mountains on the 30.01.17.

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 is all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.

Prior to LIDAR analysis this hill was listed with c 20m of drop based on the 409m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 389m based on interpolation of bwlch contouring between 380m – 390m.

The name of the hill is Mynydd Ty’n y Fach and it is situated in the Cadair Idris range of hills and is placed in the Region of North Wales (Region A, Sub-Region A3).  The hill is positioned between the stream valleys of the Afon Cadair to the west and the Afon Dysynni to the south-east, and has the small community of Abergynolwyn to its south south-west.

Mynydd Ty'n y Fach (SH 687 097)

As the summit of the hill is a part of designated open access land permission to visit does not need to be sought, and there are a number of public footpaths accessing the open access land from a variety of directions.

The deletion of Mynydd Ty’n y Fach from 4000m Sub-Pedwar status is due to LIDAR analysis conducted by Myrddyn Phillips.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

1m DTM LIDAR analysis gives the hill the following details:

Mynydd Ty’n y Fach

Summit Height:  408.0m (LIDAR)

Summit Grid Reference:  SH 68788 09702

Bwlch Height:  389.5m (LIDAR) 

Bwlch Grid Reference:  SH 69048 09685

Drop:  18.6m

LIDAR image of Mynydd Ty'n y Fach

Therefore, the 408.0m LIDAR analysis produced for the summit position at SH 68788 09702 and the 389.45m LIDAR analysis produced for the bwlch position at SH 69048 09685 gives this hill 18.6m of drop, and as the drop is below 20m it is insufficient for this hill to retain its 400m Sub-Pedwar status, with the details from the Trimble GeoXH 6000 survey being 408.4m (converted to OSGM15) summit at SH 68787 09703 and 389.5m (converted to OSGM15) bwlch at SH 69047 09685, giving this hill 18.9m of drop.

The full details for the hill are:

Cardinal Hill:  Cadair Idris 

Name:  Mynydd Ty’n y Fach

Summit Height:  408.4m (converted to OSGM15)

OS 1:50,000 map:  124

Summit Grid Reference:  SH 68787 09703

Drop:  18.9m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Ty'n y Fach

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:

Myrddyn Phillips and Aled Williams (May 2018)

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