Mapping Mountains – Summit Relocations – 100m Twmpau

Five Acres (SS 537 932)

There has been a Summit Relocation to a hill that is listed in the 100m Twmpau, with the summit height, drop and status of the hill being confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Five Acres

The criteria for the list that this summit relocation applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The name of the bounded land where the natural summit of this hill is situated is Five Acres and this was derived from the Tithe map, and it is the name that this hill is now listed by.  The hill is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and it is positioned between the B roads of the 4295 to the north-west and 4271 to the south, and has the village of Pen-clawdd towards the north.

If wanting to visit the hill permission to do so should be sought as the summit area is not a part of designated open access land, for those wishing to do so the nearest public footpath is to its south, with other possibilities via gated fields to the east.

Prior to LIDAR analysis this hill was listed with an estimated c 43m drop, with an estimated c 127m summit height based on an uppermost 125m ring contour and an estimated c 84m bwlch height based on interpolation of 5m contouring between 80m – 85m on the Ordnance Survey 1:25,000 Explorer map. 

The summit height produced by 1m DTM LIDAR analysis is 125.1m (125.059m) and this height is given to four separate points, these are positioned at SS 53779 93281 and SS 53779 93291 and SS 53774 93296 and SS 53780 93297.  LIDAR contouring indicates that these positions are a part of the existing natural summit of the hill, whilst also indicating that a higher point exists; 125.2m (125.190m) at SO 53791 93318 which is a part of a raised field boundary which is considered a relatively recent man-made construct, therefore it is the position of the natural summit that is being listed for this hill.  As the raised field boundary is higher than the natural summit of the hill this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The position of the natural summit of Five Acres

The position of the high point of the raised field boundary

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.

LIDAR image of the summit area of Five Acres with the field boundary's being distinctly shown

Close-up LIDAR image of the summit of Five Acres

The summit height produced by 1m DTM LIDAR analysis is 125.1m (125.059m) and this height is given to four separate points, these are positioned at SS 53779 93281 and SS 53779 93291 and SS 53774 93296 and SS 53780 93297.  These positions are a part of the natural summit of the hill and not given a spot height on Ordnance Survey maps, they are approximately 40 metres from the raised field boundary that LIDAR gives as higher, but this point is considered a relatively recent man-made construct.  

The full details for the hill are:

Group:  Gŵyr

Name:  Five Acres

OS 1:50,000 map:  159

Summit Height:  125.1m (LIDAR)

Summit Grid Reference:  SS 53779 93281 and SS 53779 93291 and SS 53774 93296 and SS 53780 93297 (LIDAR, natural summit) (LIDAR gives a 125.2m high raised field boundary positioned at SS 53791 93318 which is considered a relatively recent man-made construct)

Bwlch Height:  84.3m (LIDAR)

Bwlch Grid Reference:  SS 56307 93757 (LIDAR)

Drop:  40.8m (LIDAR)

Myrddyn Phillips (November 2018)