Mapping Mountains – Summit Relocations – 200m Twmpau

 

Field Above The House (SO 135 990) 

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 from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Field Above The House (SO 135 990)

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 Field Above The House 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 also the B4390 road to its north, the B4389 road to its west and the A483 road to its south-east, and has the village of Tregynon towards the west. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list, and listed with a 263m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

After the P30 lists were standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was subsequently noted that the interactive mapping on the Magic Maps and the WalkLakes websites give this hill a 265m summit spot height. 

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 summit image of Field Above The House

LIDAR analysis shows the ground at the base of a raised field boundary to be the highest on the hill, however as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill in the listings I author.  LIDAR analysis also shows the position of the natural summit of this hill and this has now been surveyed with the Trimble GeoXH 6000 and it is this result that is being prioritised for this hill. 

The Trimble GeoXH 6000 gathering data at the summit of Field Above The House

The summit height and position produced by the Trimble GeoXH 6000 survey is 264.9m at SO 13508 99039, and this position in relation to the raised field boundary shown by LIDAR analysis 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 264.9m and is positioned at SO 13508 99039, this position is given a 263m spot height on contemporary Ordnance Survey 1:25,000 Explorer maps and is approximately nine metres from where LIDAR gives the high point of the raised field boundary. 

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Carnedd Wen

Name:  Field Above The House

OS 1:50,000 map:  136

Summit Height:  264.9m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference (New Position):  SO 13508 99039 (Trimble GeoXH 6000) 

Bwlch Height:  220.0m (LIDAR) 

Bwlch Grid Reference:  SO 13331 98643 (LIDAR) 

Drop:  44.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (January 2021)