Rhiw Gwraidd (SO 016
634)
There has been a Summit Relocation that is retrospective to a hill that is listed
in the Y Pedwarau - The 400m Hills of Wales and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from a level and staff summit survey for position conducted by John Barnard, Graham Jackson and Myrddyn Phillips, a Trimble GeoXH 6000 summit survey for height and position conducted by Myrddyn Phillips and LIDAR bwlch analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.
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| Rhiw Gwraidd (SO 016 634) |
The criteria for the two listings that this retrospective summit relocation affects are:
Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills; 500m Sub-Pedwarau, 500m Double Sub-Pedwarau, 400m Sub-Pedwarau, 390m Sub-Pedwarau and the 390m Double Sub-Pedwarau. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.
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| Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams |
Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height. The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.
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| Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
The name the hill is listed by is Rhiw Gwraidd and it is adjoined to the Hirddywel group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B2), and it is positioned with the A44 road to its north and the A470 road to its south-west, and has the town of Llandrindod towards the east south-east.
When the original 400m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, the summit position for this hill was given as SO
009 633, with an accompanying note stating Two
tops of same height, other at SO 014 633.
These two tops are given 442m spot heights on the Ordnance Survey
1:25,000 Explorer map, whilst a 440m ring contour further to the east is given
a 441m spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.
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| Extract from the Ordnance Survey 1:25,000 Explorer map |
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| Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map |
When this hill was line surveyed the summit
position was found to be where the 440m ring contour is positioned on the Ordnance Survey 1:25,000 Explorer map, which is just to the east of the easternmost of the two 442m spot heights. However, its summit height was not surveyed with the Leica
equipment and therefore the hill remained with a summit
position corresponding to where the 441m spot height appears on the Ordnance
Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and yet two 442m
spot heights appear further to the west of the high point of this hill.
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| The line survey that determined the summit position of Rhiw Gwraidd |
However, it was not until the survey with the Trimble GeoXH 6000 that an accurate height could be determined. This survey gives the summit height of this hill as 441.7m positioned at SO 01606 63432, 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 high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation, within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, 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 or covered reservoir that is considered a relatively recent man-made construct, or the de-twinning of a summit, 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.
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| The Trimble GeoXH 6000 gathering data at the summit of Rhiw Gwraidd with the old position of the summit in the background |
Therefore, the height produced by the Trimble GeoXH 6000 survey to the summit of this hill is 441.7m and this is positioned at SO 01606 63432, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and is approximately 625 metres and 150m eastward from where the two 442m spot heights appear on the Ordnance Survey 1:25,000 Explorer map.
The full details for the hill are:
Group: Hirddywel
Name: Rhiw Gwraidd
OS 1:50,000 map: 147
Summit Height: 441.7m (converted to OSGM15, Trimble GeoXH 6000)
Summit Grid Reference (New Position): SO 01606 63432 (Trimble GeoXH 6000)
Bwlch Height: 229.6m (LIDAR)
Bwlch Grid Reference: SO 00812 64999 (LIDAR)
Drop: 212.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)
Dominance: 48.03% (Trimble GeoXH 6000 summit and LIDAR bwlch)
Myrddyn Phillips and Aled Williams (March 2018)
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