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

Wenlli (SH 845 655)

There has been 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 from detail on contemporary Ordnance Survey maps and hand-held GPS submissions to DoBIH.

LIDAR image of Wenlli (SH 845 655)

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 13th May 2017.

The name the hill is now listed by is Wenlli and this was derived from the Tithe map, and it is adjoined to the Rhos group of hills which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the B5113 road to its west and the A548 road to its south and east, and has the town of Llanrwst towards the south-west.

When the original 300m height band of Welsh P30 hills were 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 list. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 30m of drop, based on the twin 308m map heighted summits with the prioritised summit position given to the spot height that appears at SH 846 654 on Ordnance Survey 1:25,000 Explorer maps, and an estimated c 278m bwlch height.

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

The details for this hill were re-examined when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps.  However, as this mapping had no additional spot heights of note the details for this hill remained the same.

The details for this hill were also re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This re-assessment resulted in the hill being listed with an estimated c 277m bwlch height based on interpolation of 5m contouring between 275m – 280m and therefore increasing its drop value to c 31m.

During these re-assessments the position of this hill’s summit was relocated to match a hand-held GPS position submitted to DoBIH, and although an accurate survey would be needed to confirm this position, for now it is being taken for that of the summit.

The revised summit position comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, 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, or when the summit of the hill is in a different field compared to 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 compared to its previous listed position, 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.

Therefore, the listed summit height of this hill is 308m and this is positioned at SH 84520 65553, and this is in a different field to the previously listed summit position and approximately 100 metres north-westward from it.

The full details for the hill are:

Group:  Rhos

Name:  Wenlli

OS 1:50,000 map:  116

Summit Height:  308m (spot height)

Summit Grid Reference (New Position):  SH 84520 65553 (hand-held GPS via DoBIH)

Bwlch Height:  c 277m (interpolation)

Bwlch Grid Reference:  SH 83917 65689 (interpolation)

Drop:  c 31m (hand-held GPS via DoBIH and interpolated bwlch)

Myrddyn Phillips (March 2020)