Mapping Mountains – Summit Relocations – Y Pedwarau

Mynydd Llanybydder (SN 535 395)

There has been a Summit Relocation to a hill that is listed in the Y Pedwarau, with the summit height, position and relocation confirmed by LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

LIDAR image of Mynydd Llanybydder

The criteria for the list this summit relocation affects are:

Y Pedwarau - Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and the Introduction to the Mapping Mountains publication of this list appeared on the 30^th January 2017. 

The name of the hill is Mynydd Llanybydder it is situated in the Mynydd Pencarreg range of hills, which are positioned in the central part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the A 485 road to the west and the B 4337 road to the north-east, and has the town of Llanybydder towards the north north-west.

As the summit of the hill is a part of designated open access land it can in theory be approached from a number of directions, with the easiest via the access track to the high mast which is positioned adjacent to the summit area of this hill.  However, the summit of this hill is now located in a conifer plantation, thankfully its high point is not difficult to reach.

The summit area of this hill has a conifer plantation on its north-eastern side and open hillside on its south-western side, with the latter having an ancient tumulus on it with a triangulation pillar positioned near its high point which is given a 408.617m flush bracket height in the OS Trig Database.  Prior to LIDAR analysis it is this 408m map heighted position that was given as that for the summit in the 1^st edition of Y Pedwarau published by Europeaklist in May 2013.

Extract from the Ordnance Survey 1:25,000 Explorer map showing the summit position in relation to where the trig pillar and ancient tumulus is positioned

LIDAR summit image showing the ancient tumulus just below and to left of centre and the LIDAR summit just above and to right of centre

The Trimble GeoXH 6000 gathering data at the highest ground on top of the ancient tumulus

The LIDAR (Light Detection & Ranging) technique is highly accurate height data that is now freely available for much of England and Wales, and the area of the summit was analysed via LIDAR initially by Aled Williams and then by Myrddyn Phillips, resulting in the below:

LIDAR:  Ancient tumulus with trig pillar:  408.282m at SN 53485 39501

LIDAR:  Position in forestry:  408.510m at SN 53519 39583

LIDAR:  Summit in forestry:  408.700m at SN 53589 39599

During an on-site inspection data were gathered with the Trimble GeoXH 6000 from the highest ground on the ancient tumulus, resulting in:

Trimble:  Ancient tumulus with trig:  408.351m

The summit height produced by LIDAR analysis is 408.7m at SN 53589 39599 and its position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

Close up LIDAR summit image of Mynydd Llanybydder

LIDAR contouring implies that ground in the conifer plantation is higher than that at the ancient tumulus, therefore the relocated summit position is at SN 53589 39599 and this is approximately 150 metres north-east from where the previous listed 408m map heighted summit was given in the 1^st edition of the Y Pedwarau published by Europeaklist in May 2013 

 

The Trimble GeoXH 6000 positioned at the LIDAR summit of Mynydd Llanybydder

The full details for the hill are:

Group:  Mynydd Pencarreg

Name:  Mynydd Llanybydder

OS 1:50,000 map:  146

Summit Height:  408.7m (LIDAR)

Summit Grid Reference (New Position):  SN 53589 39599 (LIDAR)

Bwlch Height: c 287m (interpolation)

Bwlch Grid Reference:  SN 56098 40547 (interpolation) 

        

Drop:  c 122m (LIDAR summit and interpolated bwlch)

For details of the survey of this hill

Myrddyn Phillips and Aled Williams (December 2018)