The historical record is rather vague as to where the original ford was. However today we find ourselves at a working ford on the river Stour. A ford is a shallow place with good footing where a river or stream may be crossed by wading or in a vehicle. This ford can be crossed on a bicycle; the C.O. has seen it done.
When sediments (sand, gravel, clay, etc) enter the River Stour, one of two things happen to them. The sediment will either sink to the bottom (and stay there), or it will be carried along by the water’s flow. Factors determining whether the sediments fall to the bottom of the river or whether they are carried along include:
1. How fast the water is moving
2. How big the particles of sediment are
3. The density of the particle.
4. The shape of the particle.
Some of the sediment in the river Stour will be swept along with the water. The largest particles will roll or slide across the river bed whereas smaller particles will bounce along the river bed. Together the rolling, sliding and saltating grains make up what is called the bedload of the moving sediment, because they are continuously or intermittently in contact with the river bed during transport. The finest particles are caught up in the turbulent water flows and are carried in suspension; never touching the base of the river. These form the suspension load of the moving sediment. (There is no hard and fast distinction between bed load and suspended load as a faster flow will carry more in suspension).
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So… To work out how different sediment may be transported by the river we need to know the speed of the water. The speed of the water can be estimated by playing ‘Pooh sticks’. I shall assume you know the game, if not there is a link here
I have added a team work attribute to this cache as if you are going to “Pooh Stick” at the marked waypoint you will need to do it with a friend. This section of the road can be very busy. Do not try to run across this road. If you are on your own, use your GPS to mark out a point fifteen metres downstream from that little footbridge you can see.
So… Go to the start point for Pooh Sticks, and have your assistant at the end point. Drop your stick in the river. Time how many seconds it takes for your ‘Pooh stick’ to travel under the bridge, from one side to the other. (Or from that footbridge to fifteen metres downstream) The distance under the bridge is approximately fifteen metres.
To find the speed of the water current use the following formula: Speed = Distance / Time e.g. On 6th November 2013 my Pooh stick took 23 seconds to travel under the bridge. So 15 metres / 23 seconds = 0.65 metres per second Having got your answer in metres per second, multiply it by 100 to get an answer in centimetres per second. In my case I have 65 centimetres per second.
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Looking at the graph shows that clay, sand and gravel will be carried along in the water. The red line shows the speed of the water on the day I visited.
Use the graph to work out which sediment is being transported on the day you visit.
Please email me the answers to the following questions to claim this Earthcache: To claim this Earthcache you must send me the answers to the following questions via the link to my profile on the Geocaching website
1. How many seconds did it take for your 'pooh stick' to travel under the bridge?
2. What was the speed of the water on the day you visited?
3. Using the graph above which grains of sediment may have been transported? Clay, Silt, Sand, Pebbles?
4 Perhaps more importantly what sediments would not be carried but would be deposited?
5 How do you think this might change at different times of the year?
6 Bearing in mind what you have learned and looking at the river bed at the ford, do you think that this ford is a permanent feature? In time will it silt up and become much shallower, or will it erode away and become much deeper?
It is entirely your choice to do so or not, but adding photo of you and your team at the ford in your log would make me smile.