Mapping Mountains – Trimble Surveys – Hirddywel

14.12.14  Bryn Mawr (SN 944 802) and Cefn Uchaf (SN 958 800)   

Cefn Uchaf (SH 958 800)

And what contrast two days can give, yesterday was dominated by an early morning chilled frost and radiant blue sky, whist today was a grey soggy affair with wind and rain, all good fun though.

Mark wanted to bag another Hump and Pedwar to take his yearly totals to a satisfactory point and suggested combining both targets by visiting one hill; Bryn Mawr.  Its summit also needed Trimbling as it has two points of equal map height.  Mark had also spotted that its neighbouring hill which the land where the summit is situated is named Cefn Uchaf on the Tithe map, is listed as a marginal Tump that is currently a Sub-P30 in the listings I have compiled.

We were away from Welshpool by 8.45am and with only a slight dusting of moistness in the air I hoped that the forecast of rain would keep at bay until after our walk had finished; no such luck.

As we approached the outskirts of Llanidloes the wiper blades on the car were heralding a wet morning.  Mark navigated us to the area of the bwlch between the two hills, we parked above the bwlch on a corner of the narrow lane as a track headed toward our first hill of the day; Bryn Mawr.

As we set off up the track the rain skimmed across the landscape with valleys of grey below and fields of green being blown by the wind, I only had time to take a couple of photos on our way up; all were with my back to the rain trying in vain to shield the camera from the wet stuff.

Heading into the soggy stuff on the way to the top of Bryn Mawr

I’d made a note of the ten figure grid references for the two tops of this hill; both are given the map height of 405m, one appearing on the enlarged Geograph map.  By the time we reached the high point of one of them I decided it was too wet to try and find the piece of paper with the grid references on it and just plonked the Trimble down on one of the high points, set it to ‘Log’ and stood with my back to the rain and wind.

First candidate for the high point of Bryn Mawr

Just to the north and over two fences was the second high point.  However, upon closer inspection this second point has two points that vied for being the highest, thankfully as the Trimble gathered data from its second and third placements the rain ceased for a few minutes and even the temptation of lightening skies teased us, not for long though as the rain soon started again.

Second candidate for the high point of Bryn Mawr

Third candidate for the high point of Bryn Mawr

We retraced our inward route, over the two fences and down the track and past the car onto the narrow lane, this took us straight over the area of the critical bwlch for our next hill.  We had a quick look at the land as we crossed the bwlch and proceeded up another track to the summit of the second hill.

The area of the critical bwlch of Cefn Uchaf

Once at the top we were confronted by about five possibilities for the highest point, as I set the Trimble to ‘Log’ on the first we arrived at, Mark ventured into the rain to assess some of the other candidates, as the five minutes of data collection neared its end I looked over at Mark on one of the other high point contenders and he was pointing toward me, signifying that the point he was on was lower than where I was.  However, a little further east from the first high point we had reached was another high point, I walked over and stood on its top and it looked as if it was higher than other contenders, Mark thought likewise when he joined me.  However, there were at least two other points of similar height.

First candidate for the high point of Cefn Uchaf came to 357.4m (357.370m converted to OSGM15) at SN 95800 80082, with Mark in the background on another candidate for the high point

Second candidate for the high point of Cefn Uchaf came to 357.4m (357.428m converted to OSGM15) at SN 95873 80107

As I packed the Trimble away after gathering data from the second high point we headed back down the track to the connecting bwlch.  The track led onto a corner of the narrow lane, where the track and lane intersect was a pool laden mud swamp.  We assessed the lane and decided that the critical bwlch lay just south of the corner in the road.  We also decided that the hill to hill traverse indicated that the critical bwlch was in the middle of the road.  So as the rain started to get heavier I set the Trimble up and we each stood about 30 metres down road from it, Mark on the southern side and me on the northern, each ready to flag down any approaching car.  Thankfully none appeared and after I took a few photos of its set up position I packed it away and we soggily made our way back up the lane to the car.

Looking south from the corner of the lane as it intersects with the track

Looking north toward the track and lane intersection

As it was only 12.20pm we decided to head into Llanidloes and visit the Red Lion, which serves Sunday roasts for £5.00, which is excellent value.  We sat with our plates full of food, mine seemed to be spilling over the sides with is always a good sign. 

Highly recommended, the £5.00 Sunday dinner at the Red Lion in Llanidloes

Postscript:  Since the survey of these hills, the LIDAR (Light Detection & Ranging) technique is now being used to produce accurate height and position for hills.  Subsequently these hills have been analysed via LIDAR and it is this result that is being prioritised in preference to that produced by the Trimble GeoXH 6000 surveys.

Survey Result:

Bryn Mawr

Summit Height:  406.2m (LIDAR)

Summit Grid Reference:  SN 94489 80295 (LIDAR)

Bwlch Height:  c 292m (interpolation)

Bwlch Grid Reference:  SN 94116 79772 (interpolation)

Drop:  c 114m (LIDAR summit and interpolated bwlch)

Dominance:  28.11% (LIDAR summit and interpolated bwlch)

Cefn Uchaf (significant name change)

Summit Height:  357.7m (LIDAR)

Summit Grid Reference:  SN 95819 80021 (LIDAR)

Bwlch Height:  329.3m (LIDAR)

Bwlch Grid Reference:  SN 954212 80193 (LIDAR)

Drop:  28.4m  (LIDAR) (Trichant reclassified to Sub-Trichant) 

Dominance:  7.93% (LIDAR)

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