This is a simple Earthcache. The aim of it is to make you take a closer look at the world around you, and to make you remember a geography lesson many moons ago when your teacher was trying in vain to get you interested in river features. You remember, the one where you convinced yourself that it would never, ever be of any use in the real world.
Well here is the teacher's revenge.
To log this Earthcache you will have to learn about the processes that shape the earth and in particular the features created by moving water. You will learn to identify some of these features and, using this recently re-acquired knowledge, you will be able to answer the questions posed below.
We hope you enjoy this little journey back to your childhood.
The Geography Lesson
Rivers play a key role in shaping the land. Through erosion and deposition they move rocks and soils around the landscape.
One of the classic features of lowland rivers is the meander. A meander is a loop-like bend in a river. It seems strange that the water doesn't just run in a straight course downhill, but you can demonstrate meandering quite easily by tipping a jug of water slowly down a sheet of wood, glass or metal. You will only see a straight course of water if the sheet is at a steep angle. At a shallow angle the water will wander from side to side. You can demonstrate this even better with a layer of sand over a slightly sloping surface, and a hose-pipe.
In a real meander the outer bank is eroded away because here the water is deeper and flows more quickly. It undercuts the bank and makes it steeper through incremental collapses. The net effect is that meanders get more pronounced as time passes, and the outer bank will be at the steepest angle that the soil material can support. It may well be vertical at times, and is referred to as a river cliff.
On the inner bank we see a much slower flow and hence we get deposition. A gentle slip-off slope will develop where faster flowing water slows down and can no longer carry the material eroded from the outside.
As more erosion takes place there comes a point where the river breaks through the narrowing loop and resumes a straighter course. This quite often happens at times when the river is in spate and its erosive force is much greater. A little looped or semi-circular lake is left behind, commonly known as an ox-bow lake.
In the flood plains of rivers like this you can often also find abandoned channels from previous stages of erosion and deposition. The river is constantly changing its channel.
Some Classic Undercutting
The River Ouzel - Top to Bottom
The River Ouzel (also known locally as the Lovatt) rises as a chalk stream from a spring near the Dunstable Downs. It flows northwards and near Leighton Buzzard it cuts through the Greensand Ridge. From there it meanders its way northwards into Milton Keynes, where it has largely been tamed by the balancing lakes at Caldecotte and Willen. Around Willen Lake its course has also been altered and straightened. From Willen it meanders a little more until it joins the Great Ouse at Newport Pagnell. The section of river we are studying is between Caldecotte and Willen balancing lakes and upstream of the straightened section. The balancing lakes act mainly to capture the fast surface run-off from the new city, and therefore act to reduce the number of very serious floods. The river therefore behaves more like it would if the city was not present at all.
Reedbeds
The River Ouzel – A History
Todays river is too small and too passive to cut such a large valley. In fact, if you stand at the current river you can’t really tell you are in a valley. The closest river terraces are maybe 150m away towards Woughton on the Green. This is an indicator that the river once carried a lot more water than it does today.
Half a million years ago at the end of the Anglian glaciation vast amounts of water were released from the melting ice masses. This water gushed along the valley here, carrying large amounts of silt, sand and gravels. These sediments were deposited as the water slowed and became unable to support its weight.
The River Ouzel - A Morphology
The River Ouzel is an alluvial river. Alluvial rivers deposit sediments along their length. The Ouzel has cut through layers of boulder clay deposited during the retreat of the Anglian ice sheets. This boulder clay overlies the older Oxford Clay deposits beneath. The beds and bank are made up of river sediment which is of a fairly even, and small, grain size. The few pebbles that do exist are quite rounded. This is an indicator of constant rework by the river. In a “new” more recent boulder clay deposit we would see an uneven mixture of grain sizes and much more jagged rocks. From this we can infer that the Ouzel has been in this valley for some time.
The Floodplain
The River Ouzel – Round The Bend
To log this Earthcache there is some field observation to be done, so you will need to make a visit to the site and have a look around. Access should be easy at all times unless the river is in flood. There are several gravel paths running through the park here, and one of these runs past all of the listed waypoint positions. You can reach the start point on paved routes from either Monkston Park, or from the car park in Woughton on the Green (the “Parking” waypoint).
All of the river features described in the Geography Lesson are visible within a few hundred yards just here.
To claim this Earthcache as a find, please email the cache owner with the answers to the following questions. Please don’t upload them into your log.
Start at the information board at the given coordinates.
- Move to waypoint Position 1, a few yards in front of you. Provide a short description of what you can see here. Be sure to describe which of the river features you are standing on, and which you think is on the opposite side. There are two names for the feature you are standing on. Please provide them both.
- Now move to waypoint Position 2, about 100m to the North. Please describe the river feature you see here. Estimate its length and breadth in metres. What do you think will eventually happen here? Which of the photos on this page did I take from this location?
- Now move to waypoint Position 3, about 400m South. What feature do you think this is? Estimate its depth and width in metres. Is it possible to follow this feature all the way back to the river further upstream?
- Try to find the position I was standing in when I took the "Classic Undercutting" photo. Roughly how far from the given coordinates are you (in metres) ?
Optional Tasks
- From the riverbank near to the given coordinates you will be able to photograph the footbridge. If you would like to load a photo of yourselves standing on that bridge into your log that would be fun, but this is not required for logging the cache.
The Footbridge
Many thanks to Wavvy, who supplied the original idea and much of the content for this cache.
The most exciting way to learn about the Earth and its processes is to get into the outdoors and experience it first-hand. Visiting an Earthcache is a great outdoor activity the whole family can enjoy. An Earthcache is a special place that people can visit to learn about a unique geoscience feature or aspect of our Earth. Earthcaches include a set of educational notes and the details about where to find the location (latitude and longitude). Visitors to Earthcaches can see how our planet has been shaped by geological processes, how we manage the resources and how scientists gather evidence to learn about the Earth. To find out more click HERE.