Mapping Mountains – Summit Relocations – 200m Twmpau

 

Parkhouse Rocks (SO 499 034) 

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived by Joe Nuttall who produced a summit analysis programme using LIDAR, and then by LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips. 

LIDAR image of Parkhouse Rocks (SO 499 034)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub category entitled the 200m Sub-Twmpau consisting of all Welsh hills at or above 200m and below 300m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Parkhouse Rocks, and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is encircled by minor roads with the B4293 road further to its north-west and the A466 road further to its east, and has the small community of Llanishen towards the west and the village of Llandogo towards the east north-east. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the qualifying hill was included in the main P30 list under the name of Ninewells Wood Top, and listed with a 274m summit height, based on the spot height that appears at SO 509 033 on the Ordnance Survey 1:25,000 Explorer map. 

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. 

LIDAR image of the old summit position

The summit height and position produced by LIDAR analysis is 276.1m at SO 49959 03439, and as this is higher than the previously listed summit positioned to the east it comes within the parameters of the Summit Relocations used within this page heading, these parameters are: 

The term Summit Relocations applies when the hill’s high point is found to be positioned; in a different field, to a different feature such as in a conifer plantation, placed within a different map contour, to a different point where a number of potential summit positions are within close proximity, or when natural ground or 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, 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. 

Therefore, the new listed summit height for this hill is 276.1m and is positioned at SO 49959 03439, this position is not given a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and is 1,000 metres westward from where the previously listed summit is positioned.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Gwent Is Coed

Name:  Parkhouse Rocks

OS 1:50,000 map:  162

Summit Height:  276.1m (LIDAR) 

Summit Grid Reference (New Position):  SO 49959 03439 (LIDAR) 

Bwlch Height:  235.2m (LIDAR) 

Bwlch Grid Reference:  SO 50941 04537 (LIDAR) 

Drop:  40.9m (LIDAR)

 

Myrddyn Phillips (February 2021)