Mapping Mountains – Summit Relocations – 200m Twmpau

Crasty Frain (SO 109 983)

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 initially confirmed by LIDAR analysis instigated by Joe Nuttall who produced a summit analysis programme, and then by LIDAR analysis conducted initially by Jim Bloomer and subsequently by Myrddyn Phillips, with the summit later surveyed with the Trimble GeoXH 6000 and which was conducted by Myrddyn Phillips.

Crasty Frain (SO 109 983)

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 Crasty Frain and this was derived from the Tithe map, 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 positioned with a minor road to its north and the B4389 road to its south-west, and has the village of Tregynon towards the west north-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 accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 list, with its summit listed at SO 107 981 which compliments the position of the 253m spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 27m of drop, based on the 253m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 226m bwlch height, with the latter based on interpolation of 10m contouring between 220m – 230m.

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.

The summit relocation of this hill was initiated by Joe Nuttall who produced a summit analysis programme that used LIDAR with an alternative height map (DEM) allowing identification of summits and cols and thereby drops.  The resulting spreadsheet that Joe produced contains over 29,600 hills.

LIDAR image of Crasty Frain

This spreadsheet is being evaluated by a number of people, and for this particular hill it was Jim Bloomer who initially assessed this hill’s data against that produced via LIDAR.  Myrddyn Phillips then evaluated the details for this hill via LIDAR analysis and confirmed its summit height and position and hence its relocation and reclassification to 200m Twmpau status.  The summit of this hill has now been surveyed with the Trimble GeoXH 6000 and it is this evaluation on the hill and the subsequent survey that is being prioritised.

LIDAR summit image of Crasty Frain

The summit height and position produced by the Trimble GeoXH 6000 survey is 256.3m at SO 10995 98318, and this 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 when the hill’s high point is in a different field, or where a number of potential summit positions are within close proximity and the highest point is not where previously given, or when it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour, 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 256.3m and is positioned at SO 10995 98318, this position is not given a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps but compliments the height and position of the 256m spot height that appears on the mapping available on the Magic Maps and the WalkLakes websites, and is approximately 250 metres north-westward from where the previously listed summit is positioned. 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Carnedd Wen

Name:  Crasty Frain

OS 1:50,000 map:  136

Summit Height:  256.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference (new position):  SO 10995 98318 (Trimble GeoXH 6000)

Bwlch Height:  226.1m (LIDAR)

Bwlch Grid Reference:  SO 10787 98754 (LIDAR)

Drop:  30.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (October 2020)