In this investigation, I will be investigating changes along the long profile of a river. The river I will be studying is Barley Water which is located in the north-east of New Forest National Park in southern England. Bartley Water is a tributary of the River Test and it is 27 km in length including all its smaller tributaries. It runs from Bartley to Eling and flows east into Southampton Water which goes into the Solent. The catchment area goes around the edge of Bartley, Minstead and Ashurst and through parts of Totton and Eling, equalling a total area of around 40 km2.
The source of Bartley Water is 37m above sea level. Bartley water is a third-order stream (also called a headwater stream) and has a drainage density of 0. 675 km/km2 showing it is low density so the drainage basin is likely to be permeable rock, for example, chalk, have much vegetation cover, limited rainfall, gentle slopes and a lower channel frequency. There are three main sites along the river that I will visit in order to collect appropriate data to answer the question.
First is site 1, which is only 0. km away from the source of the river, situated at Busketts Lawn Inclosure, grid reference 309 109. Site 2 is near the middle course of the river, in the Woodlands area, grid reference 325 106. Lastly, I will go to the mouth of the river, at the Tide Mill in Eling, grid reference 362 123. There are more details about these site locations on the maps which I have annotated. Upper course features: In the upper course of Bartley Water, I would expect to see V shaped valleys as I can see from the contour lines on the map.
They are created by vertical erosion in the upper course of the river due to the steeper gradients. In the upper course, vertical erosion is more dominant than lateral erosion so as the river flows downhill very quickly, they remove more sediment from the bottom rather than the sides of the stream channel, down cutting it into a V shaped valley. Interlocking spurs may also be found. These form when the river bends to avoid areas of hard rock.
When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form which is another feature found in the upper course of a typical river. However, I don’t expect to see this because the gradient of Bartley Water is small compared to that of other rivers and a steep gradient is required to create waterfalls. Middle course features: The middle course of a river has more energy and a high discharge. The gradient here is lateral as the ground is no longer that steep, so the river erodes laterally and causes bends. A bend in the river is called a meander.
The force of the fast-flowing river undercuts the banks on the outside of the meander causing an overhang of land called a river cliff but on the inside, water flows slower so it doesn’t have enough energy to carry the sediment which is therefore deposited. A slip off slope or point bar is formed here which is another typical feature of the middle course that can be found in Bartley Water. Over time, as the meanders get wider the ends become closer together. During a flood when the river has a higher discharge and more energy, the ends join and the bend is cut-off from the main river channel.
This is called an oxbow lake. There is no evidence of an oxbow lake on the map so I am not expecting to see one at Bartley Water. Lower course features: Floodplains may form on the lower course of Bartley Water. This is an area around the river that is covered when the river floods. It is a fertile area because of the alluvium (fine layers of clay, silt and other sediments that are deposited when the river floods) which makes it a good place for agriculture. In fact, if the alluvium is stable enough to support vegetation, salt marches may form.
A build-up of alluvium can create levees, another lower course feature, which raises the river banks. Artificial levees may also be built to reduce the impacts of flooding. Another feature that could be formed is a delta. This forms when river mouths become choked with sediment, causing the main river channel to split into hundreds of smaller channels. However, I don’t think Bartley Water has this because it cannot be seen on the map and also it doesn’t fulfil the conditions for a delta to form. There are many ways in which a typical river changes along its long profile.
The Bradshaw Model can be used to demonstrate this. As the river goes downstream, the discharge, occupied channel width, channel depth, average velocity and load quantity increases, but load particle size, channel bed roughness and slope angle (gradient) decreases. I will be investigating four key questions using the Bradshaw Model for Bartley Water to see if the same relationships can be seen: 1. Does velocity increase as you go downstream? This should be true because more tributaries are added as the river flows downstream.
This in turn increases the wetted perimeter of the river so less water is in contact with the bed of the river and the mouth and there is less energy used to overcome friction. The extra energy is used to move the water and hence the river goes progressively faster on their journey downstream. 2. Does friction decrease as you go downstream? Friction should decrease along the long profile of a river because at the upper course, there should be a lot of vegetation and large boulders on the banks and bed of the river and the river doesn’t have enough energy to overcome this.
However, as you go downstream, the velocity increases and there are less weeds and stones to overcome so there is less friction. In addition, as the wetted perimeter increases downstream, less water is in contact with the bed and banks so friction also decreases this way. 3. Does the occupied channel width increase as you go downstream? As you go from the upper course to the lower course more tributaries joins the river so the velocity and the amount of water it needs to carry (discharge) increases so a larger space is needed for the larger volume of water.
In addition, the river has more energy the further downstream you are and this has the potential to erode the river laterally (as opposed to vertically as the river reaches less steep ground) so the channel width increases. 4. Does load size decrease as you go downstream? Linking to one of the other questions, because the velocity increases downstream, the river has more energy which allows the river to pick up heavier and larger sediment and erode it down by the processes of abrasion and attrition.
The amount of energy increases downstream so the rate of erosion will also increase causing the load to become smaller and more rounded. In addition, by the time the sediment has reached the lower course, erosion would have been happening for a long time so pebbles and stones in the river will be smoother and smaller in the lower course than in the upper course. In addition to these, I will be investigating a question of my own: 5. How does the gradient (slope angle) change as you go downstream? The gradient of the river bed is the ratio between vertical fall over horizontal distance.
The gradient should decrease as you go downstream because the river meanders along the land rather than erode into it and follow a straight path. Therefore, it covers a decrease in height over a longer distance the further downstream you get. Key Words Abrasion: Bits of rock and sand in the river grind down river banks and river beds like sandpaper. Alluvium: load particles (clay, silt, sand and gravel) deposited by a river. Attrition: Water smash rocks and pebbles on the shore into each other, and they break and become smoother. Discharge: The amount of water in a river at any given point and time.
It is measure in cumecs (cubic metres per second). Friction: A force that is created when water comes into contact with vegetation/ rocks in the river. It resists the relative movement of the river. Gradient: the slope or steepness of the river profile. Hydraulic radius: Ratio between the wetted perimeter and the cross-section area. Load: the sand, pebbles, boulders, or other debris transported by the river. Velocity: The rate of water movement, often measured in metres per second. Wetted perimeter: The perimeter of the cross sectional area (banks and bed) that is in contact with the water.
