Showing posts with label Gewni. Show all posts
Showing posts with label Gewni. Show all posts

Wednesday, 29 August 2018

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


Gewni (SM 796 236) – Dominant addition

There has been confirmation of an addition to the listing of Y Trechol – The Dominant Hills of Wales due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

Y Trechol – The Dominant Hills of Wales - Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

This hill did not appear in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website, as it was thought not to have 30m of drop and therefore was not considered for Dominant status.

Gewni (SM 796 236)

This hill was included as a P30 and a Dominant hill shortly after the Ordnance Survey Interactive Coverage Map became available on the Geograph website, and prior to LIDAR analysis it was listed with 35m of drop based on the 35m summit spot height that appears on this map.

The name of the hill is Gewni and it is a tidal island that is attached to mainland Wales at low tide.  The hill is adjoined to the Carn Llidi group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), with the island being positioned to the west of where the Afon Solfach (River Solva) enters the sea, and has the village of Solfach (Solva) towards its north-east.

If wanting to visit the hill it is a part of designated open access land, for those wishing to do so caution is advised as the easiest approach will probably necessitate some form of scramble.

The confirmation of the addition of Gewni to Dominant status is due to LIDAR analysis conducted by Myrddyn Phillips.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The 1m DTM LIDAR analysis gives the hill the following details:


Name:  Gewni

Summit Height:  35.7m

Summit Grid Reference:  SM 79696 23606

Bwlch Height:  0.3m

Bwlch Grid Reference:  SM 79689 23698

Drop:  35.3m

Dominance:  99.11%


LIDAR image of Gewni

Therefore, the 35.65m LIDAR analysis for the summit position at SM 79696 23606 and the 0.3m LIDAR analysis for the bwlch position at SM 79689 23698 gives this hill 35.3m of drop and 99.11% dominance, which is sufficient for Dominant status.


The full details for the hill are:

Group:  Carn Llidi

Name:  Gewni

Dominance:  99.11% (LIDAR)

OS 1:50,000 map:  157

Summit Grid Reference:  SM 79696 23606 (LIDAR)

Summit Height:  35.7m (LIDAR)

Bwlch Grid Reference:  SM 79689 23698 (LIDAR)

Drop Summit to Bwlch:  35.3m (LIDAR)

Drop Bwlch to ODN:  0.3m (LIDAR)


Myrddyn Phillips (August 2018)






Friday, 24 August 2018

Mapping Mountains – Hill Reclassifications – 30-99m Twmpau


Gewni (SM 796 236) – 30-99m Twmpau addition

There has been confirmation of an addition to the 30-99m Twmpau list due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 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.

This hill did not appear in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website as it was thought not to have 30m of drop and did not meet the criteria then used for the sub category; however this sub list has now been standardised including the addition of interpolated drop values and heights.

This hill was included as a P30 shortly after the Ordnance Survey Interactive Coverage Map became available on the Geograph website, and prior to LIDAR analysis it was listed with 35m of drop based on the 35m summit spot height that appears on this map.

The name of the hill is Gewni and it is a tidal island that is attached to mainland Wales at low tide.  The hill is adjoined to the Carn Llidi group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), with the island being positioned to the west of where the Afon Solfach (River Solva) enters the sea, and has the village of Solfach (Solva) towards its north-east.

Gewni (SM 796 236)

If wanting to visit the hill it is a part of designated open access land, for those wishing to do so caution is advised as the easiest approach will probably necessitate some form of scramble.

The confirmation of the addition of Gewni to 30-99m Twmpau status is due to LIDAR analysis conducted by Myrddyn Phillips.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The 1m DTM LIDAR analysis gives the hill the following details:


Name:  Gewni

Summit Height:  35.7m

Summit Grid Reference:  SM 79696 23606

Bwlch Height:  0.3m

Bwlch Grid Reference:  SM 79689 23698

Drop:  35.3m


LIDAR image of Gewni

Therefore, the 35.65m LIDAR analysis for the summit position at SM 79696 23606 and the 0.3m LIDAR analysis for the bwlch position at SM 79689 23698 gives this hill 35.3m of drop, which is sufficient for 30-99m Twmpau status.


The full details for the hill are:

Group:  Carn Llidi

Name:  Gewni

OS 1:50,000 map:  157

Summit Height:  35.7m (LIDAR)

Summit Grid Reference:  SM 79696 23606 (LIDAR)

Bwlch Height:  0.3m (LIDAR)

Bwlch Grid Reference:  SM 79689 23698 (LIDAR)

Drop:  35.3m (LIDAR)


Myrddyn Phillips (August 2018)





Monday, 22 August 2016

Mapping Mountains – Trimble Surveys – Pembrokeshire Islands


24.07.16  Green Scar (SM 796 226)    

Green Scar (SM 796 226)

Another island adventure organised by Adrian Rayner off the Pembrokeshire coast in the capable hands of Venture Jet, we met just before 9.00am at St Justinian’s which is situated west of St David’s and is the departure point for boats visiting Ynys Dewi (Ramsey) and where the RNLI Lifeboat Station is situated.  The weather was not ideal with coastal drizzle and grey murk predominating, however it was good enough to set off and with three islands scheduled to visit we skimmed across the water toward the first; Emsger (South Bishop).

Leaving St Justinian's aboard the Venture Jet RIB with (L-R) Tony, Alex, Adrian, George and Alan

I’d visited Emsger (South Bishop) once before in mid-May of this year when the sea was calmer and the blue sky and sun gave us a window of opportunity for an unrushed visit.  Today as the RIB headed off in to the bleakness and the lighthouse atop the island came in to view the waves chopped against the steep lower rock of the island and the swell did not look inviting.

As we neared the landing place the RIB was maneuvered in to place and three people stood up; Alex, Doug and Tony, with Alan and George deciding to sit this one out as the landing looked a little unwelcome due to the swell.  Also on board were Adrian, Rob, Jon and myself and as we’d all visited the island in May we also decided to remain on board.

As the boat neared the landing place and instruction given for Alex, Doug and Tony to each in turn make the step ashore, the boat reared up as the swell hit the island, all three made it and the RIB was then positioned away from the rock and remained relatively sheltered from the waves hitting the west of the island.

We couldn’t linger as there were another two islands to attempt a landing on, and so within a few minutes of being dropped off Alex, Doug and Tony were back down waiting to be plucked off the rock and make the step from solid ground back on to the RIB.  The RIB was again maneuvered in to place as the swell reared up necessitating  it to back off and try again, this happened a few times before instruction was given to come aboard.  As Alex made the step from relatively dry land toward the RIB the swell took the boat away from the landing spot and although Alex made it safely on board, he only just did so.  This proved a foreteller of what was to happen next as the RIB again approached the rock and Doug waited, as he made his move the swell took the RIB away from the rock and Doug stepped out in to thin air and disappeared in to the sea.

As it was raining I was protecting my camera and didn’t turn round to see where Doug was, but he was definitely sea bound.  I sat and hoped that he was OK.  The RIB was quickly driven away from the rock protecting Doug from being squashed between both and turned round to be beside him, the life jacket worked perfectly and had inflated on impact.  Within a minute or so Doug had been brought on board and he quickly stripped off two outer layers and put on a dry fleece and outer water proof jacket that were stored on board.  Thankfully he was all right, dampened by the experience we continued east toward our next island; Green Scar.

Doug after his dunking back on board and in dry clothes

Green Scar lies off the southern coast of St Brides Bay and is adjacent to the harbour feeding south from the small community of Solfach (Solva).  Today it was a forlorn place, devoid of sunshine it reared up out of a grey landscape where sky and sea met.

We were brought around to the eastern part of the island seeking shelter from the westerly bash of sea upon rock.  The island was another impressive bastion of lower rock crowned by greenery with a multitude of Gannets circling overhead, and the occasional Cormorant resting on the rock.

The eastern part of Green Scar

There weren’t many places to land safely but eventually a spot was singled out that was relatively sheltered and where the rock would not bottom out the RIB when nestled against it for our landing.  The main problem was our onward route beyond the landing spot as there wasn’t much to cling on to when dropped off, but soon Jon and Rob were on the island and finding hand and foot holds and by the time I joined them they were above the main difficulty and on slanting rock which gave relatively safe passage toward the summit of the island.

Much of the ascent required a steadying hand on rock, and these were covered in bird goo, as indeed was much of the island, it seemed to ooze out of every crevice and added some unwelcome interest to the ascent.  The high pint has the remains of a small cairn on it and soon the Trimble was positioned in place gathering its customary five minutes of data.

Gathering data from the summit of Green Scar

During Trimbling time the others investigated the westerly arm of the island which was connected to its higher easterly bulk by what looked like a slender land bridge.  As they neared its high point the last of the 300 data points were stored and I switched the equipment off. 

Looking toward the westerly point of the island

Although the ground beyond the westerly arm looked easier for us to get back on to the RIB, the others slowly made their way back across the slender land bridge and we descended through the bird goo to the waiting RIB.  The slither down the final rock and the last landlocked point where just one foot was resting before that final step out in to the void wasn’t as bad as I had expected and we all made it safely on board.

Only Gewni remained to visit, this is a tidal island to the north of Green Scar and Rob and a few others had previously investigated its connection to the mainland and thought it precarious.  By the time we arrived beside the island and investigated the landing opportunities the grey conditions pervaded all around, we remained on this side of the island and went back and forth looking for a safe place to land but it was decided that the day’s conditions weren’t conducive and the island and its summit would have to wait for another day.

Gewni (SM 797 236)

To the right of the arch is where Gewni is connected to the mainland at low tide

Going through the arch

Therefore we skimmed back to St Justinian’s with two out of three islands visited, one person a little wetter than planned and another part of this beautiful coastline investigated.

(L-R) Tony, Alex, Adrian, George, Alan, the skipper, Jon, Doug and Rob
 
Survey Result:


Green Scar 

Summit Height:  36.5m (converted to OSGM15)

Summit Grid Reference:  SM 79641 22648

Bwlch Height:  N/A

Bwlch Grid Reference:  N/A

Drop:  36.5m (converted to OSGM15)

Dominance:  100.00%