The Dead Waters...
Parking is available at N56 21.908 W003 26.725, where you can squeeze your car in alongside the wall. Please don’t block farm or house entrances. Follow the track past the cottages towards the arc of trees until you reach the co-ordinates. Depending on whether it is open or closed, you may have a wooden gate to negotiate. (A polite way of saying you'll have to climb over it!)
The stretch of water you are looking at is not actually the river, although it certainly used to be. It has been cut off from the main River Earn to form what is known as an Oxbow Lake. But let's start at the beginning...
The River Earn flows from Loch Earn in the west, beginning its journey at St.Fillans. It runs south and east through Strathearn for a distance of about 46 miles (74 km) before merging with the River Tay near Abernethy and continuing on to the North Sea. Despite the sea being almost 20 miles away, the Earn is a tidal river, with the limit of its tidal reach extending to just a short distance to the east of here.
The latter part of the river’s journey through Strathearn is generally over flat and broad floodplains such as you see here, resulting in the river meandering considerably. (The word 'meander' derives from the Menderes River in western Asia Minor, renowned for its serpentine flow.)
A meandering river is constantly changing however. At a bend of a river, deposition of sediments carried in the water occurs on the convex bank (the ‘inside’ bank of the bend with the lesser radius). On the concave bank (the ‘outer’ bank of the meander and the one with the greater radius), erosion and undercutting occur. On many rivers, this action results in the concave banks being steep and almost cliff-like (referred to as Cut Banks or River Cliffs) while on the convex banks Slip-off Slopes or Point Bars are formed. This process is demonstrated in the diagram below.
A River Meander
Erosion is greater on the outer side due to the faster flowing water and because the soil is not protected by deposits of sand and rocks, whereas the inner bank continues to receive such sedimentary deposits due to the slower moving water not being able to hold on to its sediment.
Therefore, the meander tends to grow in the direction of the outer or concave bank.
Some meanders are so sharp that the river doubles back on itself and forms a loop, leaving a narrow piece of land at its neck. With erosion continuing on the two outer banks at the neck of the meander, the neck eventually wears away and a surge of water, often occurring during flooding, breaks through the neck, straightening the river and essentially making the loop redundant.
Over time, deposits build up at the neck of the loop, cutting it off completely from the river, resulting in an Oxbow Lake.
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Oxbow Lake Formation
Many Oxbow Lakes dry up due to their supply of water being cut off, leaving a Meander Scar, but this one continues to be hydrated thanks in part to it being fed by a burn from the hillside behind it, but mostly due to the regular flooding this area endures. Additionally, a lock-gate is apparently situated at the west side of the Oxbow Lake which allows controlled water ingress from the adjacent River Earn, although I could not confirm this due to the presence of the railway line.
It is difficult to say when exactly this lake was formed. However, it is at least 200 years old, since the railway line which skirts its south side was constructed during the early part of the 19th Century. There are a pair of old stone bridges adjacent to the railway embankment which may have been constructed at the same time and these have obviously been built to bridge the small trickling streams that exist today and not to accommodate a full blown river. The oldest maps of the area I have found so far, which date back to the same period, also show the Oxbow Lake in existence then.
I walked the full inside arc of the lake and at the parts that are still hydrated I found a rich variety of wildlife, including herons, swans, ducks, raptors and a fantastic variety of plant and insect life. According to local residents, there is an abundance of pike in the lake, although numerous signs displayed nearby prohibit fishing in this area.
To log this Earthcache please visit this location, post a photograph of you or your GPS at the Oxbow Lake (bonus points if you capture any wildlife in the background!) and then email me with the answers to the following questions:
1. Stand on the track at the co-ordinates given and estimate how high your feet are above water level.
2. From the same location, look at the Oxbow Lake on the north side and compare it to the south side. Identify two obvious physical differences.
3. What name is given to the steep sides caused by erosion on the outer side of a meander?
4. View the cache site area in Google Satellite. The River Earn flows from left to right across your screen and bearing in mind what we've learned about erosion on concave bends, what danger will inevitably be caused by the existing meander immediately to the south west of the Oxbow Lake?
Following your visit here, if you continue west along the road to the field entrance at N56 21.972 W003 27.088, you will get an excellent panoramic view of the full arc of the lake, with the railway cutting across it and the present River Earn forming almost a mirror image meander on the other side.
Thanks for visiting and I hope you found it educational and enjoyable!
