What changes have occurred in the channel of the river Ely as it flows downstream

River travelling fast downhill

River travelling slow on flat land

In the upper course, the river twists around interlocking spurs, but now lateral erosion on the turns has formed meanders which are constantly being worn away on the outside of the bend, the river cliff, where the majority of the water is being carried, so hydraulic action continues to make the river wider.

My graph to show how velocity changes over the different survey points does not show any real pattern as it dramatically changes from one survey point to the next, but the velocity does actually slightly increase at the rivers lower course survey points. The general idea is that the speed increases in the lower course as the gradient is much flatter than previously, but my results tend to show the contrary. This can be explained with the same reason for the efficiency increase in the lower course, which is that at the lower course, there is less water in contact with friction, so more water can move naturally, which could explain a slight increase with distance from the source (See figure 1.) This could also be explained by reviewing the human interference in the river; one example is at site four (pictured), where a weir has been built to increase the velocity to prevent flooding of the surrounding land.

Upper course Lower course

Freely moving

water

Friction with bed

Figure 1 And sides

This section will highlight the corresponding change in the load size and shape, and explain why these changes occur as the river travels downstream.

The pie charts show that as the river travels away from the source, the shape of the rocks and stones changes from being sharp and angular, to a much more rounded shape. Also the compound bar graph shows how the load decreases in size with distance from the source. E.g. At Site 1 there is 6 sub angular rocks and 6 rocks over 10cm, but at Site 8 there is one sub angular rock and 0 rocks over 10cm

Diagram to show how load becomes rounder and smaller

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This downsizing and rounding of the load occurs due to transportation and erosion processes within the river. As traction carries the larger rocks and boulders along in the upper course, the process of attrition, when rocks are bumping and bashing into each other, occurs causing the sharper edges of the rocks to be chipped off and the rocks to be downsized.

The load is then more pebble-shaped, and attrition continues during saltation, until there is just mud and finer materials floating along the river, in a transportation process called suspension. Another process that can make the load smaller is corrosion, where the water dissolves the rock until it is being carried in an invisible state by the river, in a process called solution.

The river deposits the load before it reaches the state of becoming solution or fine material, during low energy conditions. This may be when the river is very flat, in a "U"shaped valley, so the flow is not fast enough to carry the load. This often happens on the slip off slope of a meander, where the flow is at its slowest. When there is a flood this material will be spread over the surrounding lands and forms fertile soil called alluvium.

My investigation set out to answer the key question: "What changes have occurred in the channel of the river Ely as it flows downstream?" I broke the investigation into two parts, first to find out the changes in the channel characteristics and then to find out the change in load size and shape.

My graphs, photos, and other data has shown that there have been many changes, which include the change in size and shape of the river valley, change in discharge in the river, and change in size and shape of the river load. I have found that the key factors to these changes are the erosion processes, the joining of tributaries and the gradient. I have found out that for the river channel itself, vertical and lateral erosion, caused by the movement of water and its load, along with the gradient, becomes a V shape at the upper course of the river, and gradually becomes a U shape as the gradient is flatter and the valley is widened and deepened. The joining of tributaries means the discharge will increase and the river valley must become wider. It also means the river will have more power and the efficiency will increase, as will the amount of erosion such as Hydraulic action. More water will be able to move freely, which was a possible explanation for the slight increase in velocity at the lower course of the river, which was unexpected. The area around the river also changes, from being surrounded by steep valleys, to a large plain, and drainage basin where the river floods in certain conditions.

The load size unsurprisingly decreased with distance from the source, and they became more rounded, which was caused by such processes as attrition, which benefited with the changes in channel characteristics, as the various transportation processes saw the larger rocks and boulders being slowly transported in the upper course, to the solution carried at the latter survey points.

From my investigation, I can see that both the change in channel characteristics and in bed load size and shape are primarily linked with the same key factors mentioned above. I have found out that one change is often the cause of another, as the channel affects the load and various factors such as discharge affect the channel. By recording and explaining all these processes, I think the question has been answered, "What changes have occurred in the channel of the river Ely as it flows downstream?"