Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Moel y Gadair (SH 521 391) – Lesser Dominant addition 

There has been a reclassification to the list of 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 Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

Moel y Gadair (SH 521 391)

The criteria for the list that this addition applies to are:

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 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Moel y Gadair and it is adjoined to the Moel Hebog group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the coast to its south and the A497 road to its north-west, and has the town of Cricieth towards the west south-west. 

When the original 30-99m 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, as it was considered not to meet the criteria then used for the main P30 category. 

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 31m of drop and 46.27% dominance, based on the 67m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 36m bwlch height based on interpolation of 10m contouring between 30m – 40m.  The details for this hill were subsequently reassessed and its drop value amended to an estimated c 30m based on an estimated bwlch height of c 37m. 

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

This hill was then surveyed on the 15^th June 2015 using the Trimble GeoXH 6000, resulting in a 66.7m summit height and a 35.9m bwlch height, with these values seemingly confirming its P30 status. 

The Trimble GeoXH 6000 gathering data at the summit of Moel y Gadair

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites. 

One of a series of surveys conducted at the bwlch on the 15th June 2015 

One of the resources recently available online is the mapping on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  This mapping had bwlch contouring between 35m – 40m, with interpolation placing the height of the bwlch as an estimated c 37m, with the 5m contouring helping to indicate the position of the bwlch. 

With the aid of a ten figure grid reference for the bwlch position taken from the 5m contouring on the OS Maps website the bwlch of this hill was re-surveyed using the Trimble GeoXH 6000 on the 23^rd February 2016, resulting in the hill being deleted from Lesser Dominant status. 

One of two surveys conducted at the bwlch on the 23rd February 2016

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. 

Initial LIDAR analysis indicated that the position of the bwlch was at SH 52007 39290, which is relatively close to where the Trimble GeoXH 6000 was placed on the survey conducted on the 23^rd February 2016.  LIDAR gives this position as 36.8m in height and when coupled with the 66.7m summit height, these values gave this hill 29.9m of drop. 

LIDAR bwlch image with the joining of the red contour positioned on the road at SH 52007 39290 

However, the 36.8m bwlch height ascertained from LIDAR is placed on an artificially raised road which is considered a relatively recent man-made construct and therefore not taken as a part of the height of the bwlch.  Further LIDAR analysis was required. 

The initial re-assessment of LIDAR was undertaken by Aled Williams and he concluded that this hill is a natural P30, with only the height of the artificially raised road excluding it from being listed as a 30-99m Twmpau.  His conclusion was that the height of the bwlch could be listed as an estimated and conservative c 36m or if using remaining natural 35.8m positioned at SH 52020 39324.  Either value classifies this hill as a P30 and a Lesser Dominant. 

LIDAR image of Moel y Gadair with the white contour placed 30m below the summit indicating this hill is a natural P30 with only the artificially raised road stopping the two respective white contours from being continuous

Having studied LIDAR, I concur with Aled’s conclusion that this hill is a natural P30, the bwlch height quoted is 35.8m positioned at SH 52013 39319.  This position is indicated as a joining on the hill to hill traverse excluding the artificially raised road and is approximately four metres from remaining natural ground. 

LIDAR image of Moel y Gadair (SH 521 391) showing the various height contours used to conclude this hill is a natural P30 and its bwlch height and position

Therefore, the addition of this hill to Lesser Dominant status is due to a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis, resulting in a 66.7m summit height and a 35.8m bwlch height, with these values giving this hill 30.9m of drop and 46.30% dominance, which is sufficient for it to be classified as a Lesser Dominant hill.

The full details for the hill are:

Group:  Moel Hebog

Name:  Moel y Gadair

OS 1:50,000 map:  124

Summit Height:  66.7m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SH 52165 39135 (Trimble GeoXH 6000) 

Bwlch Grid Reference:  SH 52013 39319 (LIDAR)

Drop Summit to Bwlch:  30.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Drop Bwlch to ODN:  35.8m (LIDAR)

Dominance:  46.30% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (March 2022)

Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

Moel y Gadair (SH 521 391) – 30-99m Sub-Twmpau reclassified to 30-99m Twmpau 

There has been a reclassification to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

Moel y Gadair (SH 521 391)

The criteria for the list that this reclassification applies to are: 

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Moel y Gadair and it is adjoined to the Moel Hebog group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the coast to its south and the A497 road to its north-west, and has the town of Cricieth towards the west south-west. 

When the original 30-99m 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, as it was considered not to meet the criteria then used for the main P30 category. 

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 31m of drop, based on the 67m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 36m bwlch height based on interpolation of 10m contouring between 30m – 40m.  The details for this hill were subsequently reassessed and its drop value amended to an estimated c 30m based on an estimated bwlch height of c 37m. 

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

This hill was then surveyed on the 15^th June 2015 using the Trimble GeoXH 6000, resulting in a 66.7m summit height and a 35.9m bwlch height, with these values seemingly confirming its P30 status. 

The Trimble GeoXH 6000 gathering data at the summit of Moel y Gadair

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites. 

One of a series of surveys conducted at the bwlch on the 15th June 2015 

One of the resources recently available online is the mapping on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  This mapping had bwlch contouring between 35m – 40m, with interpolation placing the height of the bwlch as an estimated c 37m, with the 5m contouring helping to indicate the position of the bwlch. 

With the aid of a ten figure grid reference for the bwlch position taken from the 5m contouring on the OS Maps website the bwlch of this hill was re-surveyed using the Trimble GeoXH 6000 on the 23^rd February 2016, resulting in the hill being reclassified to 30-99m Sub-Twmpau status. 

One of two surveys conducted at the bwlch on the 23rd February 2016

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. 

Initial LIDAR analysis indicated that the position of the bwlch was at SH 52007 39290, which is relatively close to where the Trimble GeoXH 6000 was placed on the survey conducted on the 23^rd February 2016.  LIDAR gives this position as 36.8m in height and when coupled with the 66.7m summit height, these values gave this hill 29.9m of drop. 

LIDAR bwlch image with the joining of the red contour positioned on the road at SH 52007 39290 

However, the 36.8m bwlch height ascertained from LIDAR is placed on an artificially raised road which is considered a relatively recent man-made construct and therefore not taken as a part of the height of the bwlch.  Further LIDAR analysis was required. 

The initial re-assessment of LIDAR was undertaken by Aled Williams and he concluded that this hill is a natural P30, with only the height of the artificially raised road excluding it from being listed as a 30-99m Twmpau.  His conclusion was that the height of the bwlch could be listed as an estimated and conservative c 36m or if using remaining natural ground; 35.8m positioned at SH 52020 39324.  Either value classifies this hill as a P30. 

LIDAR image of Moel y Gadair with the white contour placed 30m below the summit indicating this hill is a natural P30 with only the artificially raised road stopping the two respective white contours from being continuous

Having studied LIDAR, I concur with Aled’s conclusion that this hill is a natural P30, the bwlch height quoted is 35.8m positioned at SH 52013 39319.  This position is indicated as a joining on the hill to hill traverse excluding the artificially raised road and is approximately four metres from remaining natural ground. 

LIDAR image of Moel y Gadair (SH 521 391) showing the various height contours used to conclude this hill is a natural P30 and its bwlch height and position

Therefore, the reclassification of this hill from 30-99m Sub-Twmpau status and its re-instatement as a 30-99m Twmpau is due to a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis, resulting in a 66.7m summit height and a 35.8m bwlch height, with these values giving this hill 30.9m of drop, which is sufficient for it to be classified as a 30-99m Twmpau. 

 

The full details for the hill are: 

Group:  Moel Hebog 

Name:  Moel y Gadair 

OS 1:50,000 map:  124

Summit Height:  66.7m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SH 52165 39135 (Trimble GeoXH 6000)               

Bwlch Height:  35.8m (LIDAR) 

Bwlch Grid Reference:  SH 52013 39319 (LIDAR) 

Drop:  30.9m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (March 2022)

 

 

 

  

Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Moel y Gadair (SH 521 391) - Lesser Dominant deletion

This hill has subsequently been reinstated to Lesser Dominant status due to LIDAR analysis indicating this hill is a natural P30, with the raised road passing over the bwlch considered a relatively recent man-made construct; therefore it is excluded from the height of the bwlch. 

There has been a deletion from the listing of Y Trechol – The Dominant Hills of Wales due to a survey with the Trimble GeoXH 6000 and subsequent LIDAR analysis which has resulted in the hill being taken out of the Lesser Welsh Dominant list and subjected to a life of rather pitiful non dominance.

The hill is in positioned in the Moel Hebog group and is situated on the south-western outskirts of the small community of Pentrefelin, which is positioned between the towns of Porthmadog to its east and Cricieth to its south-west.

The Trimble GeoXH 6000 survey that resulted in this hill’s deletion was conducted over two days, with the hill’s summit being surveyed on the 15^th June 2015 in warm and sunny conditions, and the bwlch being surveyed on the 23^rd February 2016 on a beautiful winter’s day, with subsequent LIDAR analysis confirming the status of this hill.

If wanting to visit the hill it can be accessed from a public footpath to its south-west, but as its summit is not on open access land permission to visit its high point should be sought.

The name of the hill is Moel y Gadair and it had been listed with 45.05% dominance and a drop value of c 30m, with the latter figure the minimum required for qualification to the Dominant list.  These figures were based on a summit survey of 66.7m and an interpolated bwlch height of c 37m based on bwlch contouring between 35m – 40m.  During the 15^th June 2015 survey the contours at the bwlch were misinterpreted resulting in the second bwlch survey which was conducted on the 23^rd February 2016 and the subsequent LIDAR analysis resulting in a bwlch height of 36.8m.

Therefore, the deletion of this hill from Lesser Dominant status is due to a 66.7m summit height and a 36.8m bwlch height, with these values giving this hill 29.9m of drop which is insufficient for qualification to the Dominant list.

The full details for the hill are:

Group:  Moel Hebog

Name:  Moel y Gadair

Dominance:  N/A

OS 1:50,000 map:  124

Summit Grid Reference:  SH 52165 39135

Summit Height:  66.7m (converted to OSGM15)

Drop Summit to Bwlch:  29.9m

Drop Bwlch to ODN:  36.8m (LIDAR)  

The final nail in the coffin - the Trimble set-up position at the bwlch of Moel y Gadair (SH 521 391)  which resulted in this hill's deletion from the Lesser Dominant list

For details on the summit survey and the bwlch survey that resulted in this hill being deleted from Lesser Dominant status.

My thanks to Aled Williams for his initial LIDAR analysis

Myrddyn Phillips (February 2016)

Mapping Mountains – Hill Reclassifications – 30m – 99m Twmpau

Moel y Gadair (SH 521 391) 30-99m Twmpau reclassified to 30-99m Sub-Twmpau

This hill has subsequently been reinstated to 30-99m Twmpau status due to LIDAR analysis indicating this hill is a natural P30, with the raised road passing over the bwlch considered a relatively recent man-made construct; therefore it is excluded from the height of the bwlch.

There has been a reclassification to the listing of 30-99m Twmpau (thirty welsh metre prominences and upward) due to a survey with the Trimble GeoXH 6000 and subsequent LIDAR analysis.  The hill is listed in the 30–99m height band of Twmpau hills and is situated to the south-west of the small community of Pentrefelin, which is situated between Porthmadog to the east and Cricieth to the south-west.

The hill has been reclassified from a 30-99m Twmpau to a 30-99m Sub-Twmpau, and re-joins these ranks after being originally listed in the Hills to be surveyed Sub-List that appeared on Geoff Crowder’s v-g.me website.  On reassessment the hill was promoted to full P30 status due to bwlch contour interpolation, with a drop value of c 30m based on a summit spot height of 67m and an estimated bwlch height of c 37m.

The hill is named Moel y Gadair and its summit was surveyed with the Trimble GeoXH 6000 on the 15^th June 2015 giving a height of 66.7m.  During the 15^th June 2015 survey the contours at the bwlch were misinterpreted resulting in the second bwlch survey which was conducted on the 23^rd February 2016 and the subsequent LIDAR analysis resulting in a bwlch height of 36.8m.

Therefore, the reclassification of this hill to 30-99m Sub-Twmpau status is due to a 66.7m summit height and a 36.8m bwlch height, with these values giving this hill 29.9m of drop which is insufficient for 30-99m Twmpau status.

The full details for the hill are:

Group:  Moel Hebog

Summit Height:  66.7m (converted to OSGM15)

Name:  Moel y Gadair

OS 1:50,000 map:  124

Summit Grid Reference:  SH 52165 39135

Drop:  29.9m (Trimble summit and LIDAR bwlch)

Moel y Gadair (SH 521 391) now reclassified from a 30-99m Twmpau to a 30-99m Sub-Twmpau

For details on the summit survey and the bwlch survey that resulted in this hill being reclassified to a 30-99m Sub-Twmpau status.

My thanks to Aled Williams for his initial LIDAR analysis

Myrddyn Phillips (February 2016)

Mapping Mountains – Trimble Surveys – Moel Hebog

23.02.16  Moel y Gadair (SH 521 391, only bwlch surveyed)   

The Trimble set-up position at the bwlch of Moel y Gadair

Having surveyed the two tops of Parc y Borth (SH 558 375) my next objective was another visit to the bwlch area of Moel y Gadair.  I’d visited this bwlch in June of 2015 and misinterpreted the contours on the map and therefore the positions where I had placed the Trimble were incorrect.  Today I planned to rectify this and gather data from a further two positions and by doing so, see if Moel y Gadair has sufficient drop to remain listed as a P30 Twmpau.

I parked beside one of the two positions I wanted to gather data from, this is the entrance to a Fishery beside the busy A 497 as it heads from Porthmadog to Cricieth.  Walking north-eastward for 100 metres brought me to a letterbox which stands close to a bus shelter, having marched all around this area in June of last year and studying the map in detail as well as driving a Google Car up and down this road, it was this spot where I judged the critical bwlch to be positioned.

As I set the Trimble up a woman walked toward me with a letter in her hand, as it was duly deposited in the letterbox I asked when the next collection was, she said 11.00am, it was now 11.25am, but collections are usually late, she told me.  When I was here last summer I’d watched a postal van quickly pull up on the grass verge, empty the letterbox of its contents and just as quickly zoom away, I didn’t want this to happen whilst gathering data as the Trimble was set up on the same grass verge.  Therefore as it beeped away gathering its allotted five minutes of data I stood beside the bus shelter looking out for any late postal vans ready to flag the vehicle down and quickly gather the Trimble up before it was potentially squashed.  Thankfully the collection must have been on time as no late arrivals appeared during my time at this bwlch.

Having gathered one data set I wanted to gather another, the second being beside the entrance to the Fishery and close to where I had parked my car.  I walked back to it, tried setting the Trimble up on top of my rucksack which was positioned on top of a wall, but the light from the low sun made it difficult to see the accuracy level on the equipment’s screen, and therefore I re-positioned my car and set the Trimble up on its roof and measured a 1.40m offset.

Gathering data at the entrance to the Fishery, with the bus stop where the previous data set had been gathered on the left of the road in the background of this photograph

As the Trimble gathered data I sat in the sun enjoying life and trying to judge how long it would take me to drive toward the A5 and my next objective, which was the bwlch of a hill whose summit I’d surveyed on Christmas Eve 2013.

Postscript:  Since the survey of this hill, the LIDAR (Light Detection & Ranging) technique is now being used to produce accurate height and position for hills.  Subsequently this hill has been analysed via LIDAR.  The details produced by the Trimble GeoXH 6000 summit survey are retained; however LIDAR bwlch contouring indicates this hill is a natural P30 with LIDAR giving a height and position for a bwlch with remaining natural ground close by and indicating the road passing over the bwlch has been artificially raised.  Therefore, as the road is considered a recent man-made construct it is excluded from the height of the bwlch, with the listed height and position of the bwlch that indicated by LIDAR analysis resulting in the confirmation of this hill being classified as a P30.

Survey Result:

Moel y Gadair

Summit Height:  66.7m (c0nverted to OSGM15) (from previous Trimble GeoXH 6000 survey)

Summit Grid Reference:  SH 52165 39135 (from previous Trimble GeoXH 6000 survey)

Bwlch Height:  35.8m (LIDAR)

Bwlch Grid Reference:  SH 52013 39319 (LIDAR)

Drop:  30.9m (Trimble GeoXH 6000 summit and LIDAR bwlch) (30-99m Twmpau reclassified to 30-99m Sub-Twmpau) (Lesser Dominant deletion) (30-99m Sub-Twmpau reclassified to 30-99m Twmpau) (Lesser Dominant addition)

Dominance:  46.30% (Trimble GeoXH 6000 summit and LIDAR bwlch)

For the post detailing the summit survey of Moel y Gadair please click {here}

For further details please consult the Trimble survey spreadsheet click {here}