Mapping Mountains – Summit Relocations – Y Trichant – The 300m Hills of Wales

 

Top Field (SJ 070 055) 

There has been confirmation of a summit position whose details can be included as a Summit Relocation to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Top Field (SJ 070 055)

The criteria for the list this summit relocation affects are:

Y Trichant- The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Top Field and this was derived from local enquiry, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is encircled by minor roads, with the A458 road further to its north and the B4389 road further to its east, and has the small town of Llanfair Caereinion towards the east north-east. 

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 category. 

When the P30 lists were standardised, and interpolated heights and drop values also included, this hill was listed with an estimated c 32m of drop based on the 335m summit spot height positioned at SJ 07085 05586 and an estimated c 303m bwlch height based on interpolation of 10m contouring that appear 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 Top Field (SJ 070 055)

When on the hill the position of the summit given by LIDAR was surveyed using the Trimble GeoXH 6000 as well as another position that looked of similar height.  The second position was to an elevated mound above a small quarry and upon investigation it was decided that this was man-made.

 

The result for each position is given below: 

Natural summit:  333.257m at SJ 07082 05572 

Man-made elevated mound:  333.339m at SJ 07203 05559

 

The result produced by LIDAR analysis gives this hill a summit height of 333.1m, and as the natural summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes and this 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. 

Gathering data with the Trimble GeoXH 6000 at the natural summit of Top Field

Gathering data with the Trimble GeoXH 6000 at the man-made mound

Therefore, the listed summit height of this hill is 333.3m and its confirmed position is SJ 07082 05572, this position is given a spot height on contemporary Ordnance Survey maps and is approximately 80 metres westward from where a slightly higher man-made mound is positioned. 

 

The full details for the hill are:

Group:  Carnedd Wen 

Name:  Top Field 

OS 1:50,000 map:  125

Summit Height:  333.3m (converted to OSGM15, Trimble GeoXH 6000)                                                      

Summit Grid Reference (Confirmed Position):  SJ 07082 05572 (Trimble GeoXH 6000) 

Bwlch Height:  301.1m (LIDAR) 

Bwlch Grid Reference:  SJ 06237 05273 (LIDAR) 

Drop:  32.2m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (March 2021)