GC6RGWX Millennium Meanders (Earthcache) in South West England, United Kingdom created by Team Mojo 100

GC6RGWX ▼

A cache by Team Mojo 100 Message this owner

Hidden : 9/27/2016

Difficulty:

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Size: Size: other (other)

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Geocache Description:

A fairly simple Earthcache, suitable for those starting out with this different type of geocache. There is no physical container- instead you must answer questions of earth science interest.

This Earthcache highlights meanders of the Congresbury Yeo river and how they form.

Meanders are bends in a sinuous river. The River Yeo, like most rivers, display these bendy meanders: some of the most obvious and accessible pass through Congresbury, particularly in the fields surrounding Millennium Green.

Meanders only occur in the middle and lower courses, but never in the upper course. Both erosion of the river bank and deposition of materials in the river need to occur for meanders to form.

In the upper course, the elevation and gradient is quite steep and the river flows downhill. As a result, erosion happens vertically due to gravity.
However, in the middle course, the gradient becomes more gentle, particularly as it runs through built up and relatively flat areas, such as Congresbury.
The river still has lots of energy from the flowing water and it then uses this energy to erode the river banks laterally (horizontally) rather than vertically (eroding the bed).

A river doesn't usually flow in a straight line. Water currents are always turning to avoid obstructions in a river bed (such as boulders) and this leads to areas of a river with faster movement than others, dependent on the amount of obstructions. As water currents move around the obstructions change directions, some water is pushed towards the banks, eroding them.

The blue arrow shows the natural gradual change of a river from straight to meandering over time.

The river banks here, as you will see, are made from compacted soils, which can be easily eroded by the river. Erosion of the river bed happens by:
Hydraulic action- the sheer force of flowing water slowly wears away the banks,
Abrasion- rocks (of all sizes) carried in the river wear away the banks. As rocks tend to be harder, they generally do more erosion than the water.

Erosion happens more on the outside bend of the river, compared to the inside bend, as the water's current is faster on the outside.
As the flow on the inside of the river is slower, the river has less energy to carry material (such as fine silt and soils) so it is deposited on the inside bend. The deposited material on the inside bend of a meander (the sandy coloured bits on the diagram below) is called a point bar.

To claim a find on this Earthcache, you must answer the questions below in an email/message to me within 24 hours of logging a find. Any drastically wrong or incomplete answers or any logs from a cacher without sent answers risks their log being deleted. Any photos that reveal answers will also be deleted.

Go to the meander at GZ and answer the following questions to log the cache.

1. Estimate the width of the river at the meander's widest point.

2. Bank erosion is determined by velocity of the river. What is the water level and velocity (speed) like when you visited? Is the water level high or low?

3. What specific evidence is there at GZ that:
a) the outer bank is being eroded?
b) mud/silt material is being deposited on the inner bend (point bar)?

As part of the 13th International Earthcache Day (October 2015) I challenged myself to place an Earthcache every month until Earthcache day 2016, kicking it off with GC62T8F. This Earthcache is number 12 in that challenge (September 2016).

Additional Hints (Decrypt)

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)

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Millennium Meanders EarthCache

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