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“SEVERN MEANDERS VIEW” EARTHCACHE EarthCache

Hidden : 01/08/2008
Difficulty:
2 out of 5
Terrain:
2.5 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

The most northerly summit of the Breidden Hills is 1198 feet (365 metres) above sea level and usually has great views northwards over the flood plain of the River Severn. It is also crowned by an imposing monument called Rodney’s Pillar.

The River Severn is the longest river in England & Wales and rises on the slopes of Plynlimon Fawr in Mid-Wales. Like most rivers, in it’s upper course it is a torrent that is chiefly concerned with vertical erosion and it cuts a steep-sided ‘V’-shaped valley. In the middle part of its course a river develops mature features and the valley becomes wider through the weathering of its sides. Meanders form in the middle and lower sections of rivers where there is a lot of silt-filled water flowing fairly rapidly towards the sea. As the water flows around a bend, the river tends to accentuate the curve because the current is strongest on the concave or outer part of the curve. Maximum erosion and maybe even undercutting of the riverbank takes place here but there is little erosion, and even some deposition, on the inside of the river bend. Thus an initial ‘swing’ in the river may be transformed into a sinuous meander with a ‘cliff’ overhanging the ‘under-cut bank’ and a sloping ‘spur’ projecting from the opposite side. The initial ‘swing’ might be the result of different rock or sediment type, depth & flow variation and differences in bottom friction.

The view from this EarthCache site is of the River Severn near the start of its lower valley, as the river wanders in a series of sweeping meanders across a broad, almost level plain. It is not immediately obvious but in addition to the widening or lateral shift of the river’s course (referred to technically as divagation) each meander also tends to shift downstream. This is because the current cuts more into the upstream side of each spur. Ultimately each spur is removed leaving a low cusp or bluff overlooking the floor of the valley.

In the oldest river plains, relics of former meanders may be left behind as ‘ox-bow lakes’ or ‘cut-offs’ as the river erodes a ‘short cut’ across the ‘neck’ of a meander. In these lowest reaches of the river, the water flow is more sluggish and deposition of material occurs more than erosion. The gravel and silt left behind block off the old meander as a curved lake. Ox-bows are not present at this site, however.

To log this Earthcache e mail to say :-

1) How many meanders you think you can see from the north west, through north to the north east.

2) The confluence of the River Vrynwy with the River Severn can be seen at a bearing of 070 degrees from the summit. Does there seem to be more or fewer meanders downstream from where the two rivers join?

3) To prove you haven’t just got this information from a map look at the plaque on Rodney’s Pillar and tell me (a) how is his middle name spelled, (b) what he was the Admiral of ? (Admiral of the _______ ) & (c) in what year it was repaired? And finally

4) 4) Nearby is a viewing panorama set up by a Rotary Club in celebration of its 50th anniversary in 1997. Which Rotary Club was it?

Does a sine wave curve in the river flow count as 1 or 2 meanders? Probably 2 I'd say but it is easiest to count those bends that project in one direction and then double it.

Additional Hints (Decrypt)

Ebqarl jnf n pbybheshy punenpgre

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)