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

Coed y Gaer (SO 004 843) – Lesser Dominant addition

There has been an addition to the listing of Y Trechol – The Dominant Hills of Wales prompted by a survey with the Trimble GeoXH 6000 and confirmed by subsequent LIDAR analysis; resulting in this hill being included in the Lesser Dominant sub list.

With the criteria for inclusion to the Dominant list being those Welsh P30 hills whose prominence equal or exceed half that of their absolute height, whilst the criteria for the Lesser Dominant list are those additional Welsh P30s whose prominence is 33% or more and below 50% of their absolute height.

The details relating to the inclusion of this hill in the Lesser Dominant category are retrospective as the confirmation of its addition is dependent upon a survey with the Trimble GeoXH 6000 which was conducted on the 9^th February 2014, with the relevant post giving the survey details appearing on Mapping Mountains on the 11^th February 2014.

When the sub category of hills accompanying the Welsh P30 lists published on Geoff Crowder’s v-g.me website were standardised with interpolated drop values, this hill was listed with an estimated c 119m of drop based on its 362m summit spot height and an estimated bwlch height of c 243m, these values gave this hill 32.87% dominance, which was insufficient for it to be classified as a Lesser Dominant hill.  The drop value was subsequently altered due to a 241m bwlch spot height appearing on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, this resulted in the dominance of the hill also being amended.

The name the hill is listed by is Coed y Gaer and it is adjoined to the Hirddywel group and is placed in the Region of Mid and West Wales (Region B, Sub-Region B1) with its Cardinal Hill being Pegwn Mawr (SO 023 812), and is situated above the A 470 road and the Afon Hafren (River Severn) which are to its north, and it is positioned between the small community of Llandinam to the north north-east and the town of Llanidloes to the west.

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so a minor lane to the south of the hill gives access to steep slopes leading to the summit.

Therefore, the addition of Coed y Gaer to Lesser Dominant status was prompted by a Trimble GeoXH 6000 survey and subsequently confirmed by LIDAR analysis, resulting in a 361.0m summit height and a 239.5m bwlch height, with these values giving this hill 121.5m of drop and 33.65% of dominance.

LIDAR image of Coed y Gaer (SO 004 843)

  

The full details for the hill are:

Group:  Hirddywel

Name:  Coed y Gaer

Dominance:  33.65% (LIDAR)

OS 1:50,000 map:  136

Summit Grid Reference:  SO 00491 84393 (LIDAR)

Summit Height:  361.0m (LIDAR)

Drop Summit to Bwlch:  121.5m (LIDAR)

Drop Bwlch to ODN:  239.5m (LIDAR)

For details on the survey that confirmed the addition of this hill to Lesser Dominant status

Myrddyn Phillips (August 2017)

Mapping Mountains – Significant Height Revisions – Y Trichant - The 300m Hills of Wales and Y Trechol - The Dominant Hills of Wales

Coed y Gaer (SO 004 843)

Subsequent LIDAR analysis negates the need for this Significant Height Revision post.  However, it is being kept with the results from LIDAR analysis prioritised in preference to those from the Trimle GeoXH 6000 survey. 

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of Y Trichant - The 300m Hills of Wales and Y Trechol - The Dominant Hills of Wales, with the following details being retrospective as the survey that resulted in this height revision was conducted on 9^th February 2014.  The hill is listed as a Lesser Dominant as well as a Trichant, with the latter being the 300m height band of Twmpau (thirty welsh metre prominences and upward) hills.

The criteria for the two listings that this height revision affects are:

Y Trichant - The 300m Hills of Wales - these are the Welsh hills at or above 300m and below 400m in height that have a minimum drop of 30m. 

Y Trechol - The Dominant Hills of Wales - these are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name the hill is listed y is Coed y Gaer and it is situated in the Hirddywel range of hills to the east of Llanidloes, and the survey was conducted in the company of Mark Trengove on a particularly wet and cold day.  The hill can be accessed from a minor lane to the south of its summit; and it overlooks the A470 and the Afon Hafren (River Severn) which are to its north-west.

The height given the hill on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map is 362m, with the height resulting from the survey with the Trimble being 359.9m (converted to OSGM15).  This is not a dramatic height revision but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the surveyed height produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

LIDAR image of Coed y Gaer (SO 004 843)

The full details for the hill are:

Cardinal Hill:  Pegwn Mawr

Summit Height (New Height):  361.0m (LIDAR)

Name:  Coed y Gaer

OS 1:50,000 map:  136

Summit Grid Reference:  SO 00491 84393 (LIDAR)

  

Drop:  121.5m (LIDAR)

Dominance:  33.65% (LIDAR)

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (August 2015)

Mapping Mountains – Trimble Surveys – Hirddywel

09.02.14  Coed y Gaer (SO 004 843)

Coed y Gaer (SO 004 843)

After getting wet on Oldchapel Hill (SN 976 807) we visited the Red Lion in Llanidloes for its £5.00 carvery and then ventured outside to more rain.  It really was YUCK!!

We did have a brief conversation that centred around a large mug of tea and a slice of winter berry cheesecake in the comfort of my house in Welshpool, but we decided on driving as far as the start of the proposed second walk of the day, just to have a look and see if the rain would stop.

Rather stupidly the rain did stop and gave us encouragement that the predicted dry spell of weather had arrived.  We parked close to where a disused quarry is marked on the map at SO 002 841.  Mark’s initial plan was a there and back walk visiting both Moelfre (SN 995 829) and Coed y Gaer (SO 004 843), but as daylight hours were now against us it meant that only one of the hills was feasible and we opted for Coed y Gaer, a hill I hadn’t visited before.

The hill side above us was steep from all angles and when we set off uphill we were soon slithering downhill on steep slopes made up of wet mud; rather perversely I thought it reminiscent of a new winter mud sliding sport.

Mark on the steep slopes of Coed y Gaer with Moelfre (SN 995 829) in the background

The encouragement of the all too short dry patch of weather was soon forgotten as more bitterly cold heavy squalls of rain battered across the land.  Slowly progress was made on the steepening slopes; two fences were negotiated which gave access to the upper section of the hill.  This was very wet and as the last few metres led to the summit wet snow was falling from above.

By now my thicker winter gloves were sodden and exposing fingers to set the Trimble up on its pole adjacent to the high point of the hill was a thankless task as they ended up screaming cold once again.  The weather really was foul!

A mass of grey murk battered us when we arrived at the summit of Coed y Gaer

The equipment was set up about 7cm below the very highest point, which is in the centre of the ridge fence that also has broad fence posts in proximity and a three metre high metal pole nearby.  It’ll be interesting to see if data collection was disturbed by so many near obstacles.

During the time when the equipment was being set up and my fingers screamed with cold, Mark stood passively with his back to the rain overlooking a storm laden Severn valley.  Across the river stood Y Gaer (SO 013 873) and Gelli Hir (SN 999 883) the Twin HuMP I’d visited two days ago.  By the time the 10 minutes of data collection was almost finished the wet weather had sped down the Severn valley and the sun was bursting through the cloud.

The Trimble was set up about 7cm below the highest point (which is in the centre of the fence) to try and keep its satellite coverage clear of the fence posts and metal pole

YYYIIIPPPPEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE - sunshine!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

We headed directly south from the summit and slowly made our way down increasingly slippy slopes, Mark aimed for the car and was patient enough to allow me time to investigate the area of the bwlch.  This was just around the bend in the narrow lane.

I wanted to get data from two positions at the bwlch as contour interpolation suggests the critical bwlch is placed adjacent to a stream that ‘issues’ forth from under a road at SO 00532 83919.  When I walked to this point it was evident that the road continued its downhill progress to where a 241m spot height appears on the Ordnance Survey enlarged Geograph map at SO 00512 83885.

A very expensive accident waiting to happen - the Trimble gathering data in the centre of a road

I gathered five minutes of data from each, with the second position having the Trimble placed in the centre of the road away from the bordering hedge on either side.  It took an age to achieve its required 0.1m accuracy before activating it to gather data.  Shortly after it had gathered its five minutes of data a truck appeared on the road, a few minutes earlier and the Trimble may have ended up as road kill!

The day had proved excellent, albeit a bit wet.  Great to see Mark again, visit a couple of hills with one being a new P30 for me, and an hour away from the wet stuff in the pub with a good meal.

LIDAR summit image of Coed y Gaer (SO 004 843)

LIDAR bwlch image of Coed y Gaer

Postscript:  Since the survey of this hill LIDAR has become available.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.  Consequently the details for Coed y Gaer have been analysed via LIDAR and it is this result that is being prioritised.  With LIDAR contouring able to pinpoint the natural bwlch of this hill, and this is being used in preference to the artificially raised road.

Survey Result:

Coed y Gaer

Summit Height:  361.0m (LIDAR) (significant height revision)

Summit Grid Reference:  SO 00491 84393 (LIDAR)

Bwlch Height:  239.5m (LIDAR)

Bwlch Grid Reference:  SO 00523 83853 (LIDAR)

Drop:  121.5m (LIDAR)

Dominance:  33.65% (LIDAR) (Lesser Dominant addition)

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