Geographical Applied Understanding for River's Fieldwork

Riyadh Abdulla Applied Understanding Instructor: Mr Walker

This geographical enquiry will test a hypothesis based on a study of The River Calder. The river is located in the Bleasdale Moor Area, NW of England in the county of Lancashire.

We will test to find out if the following hypothesis is true, ‘Does the River Calder fit the Bradshaw Model.’ The Bradshaw model is in figure 1.

Map evidence to find the location of this geographical investigation is on the Ordnance Survey named “Explorer Map,” on map ‘OL41’ named ‘Forest of Bowland and Ribblesdale.’

River Calder’s background information:

The River Calder is approximately 15km; its source is located on grid reference 58485, on the Eastern side of Luddock’s Fell. The river continues NW reaching towards Bleasdale Moors.

From ‘Quarry’, the River Calder begins to meander SW passing through ‘Oakenclough’ on grid reference 5547 passing Calder Vale further south.

SW from this, the River Calder passes ‘Sandholme Mill’, intersecting with the M6 motorway around grid-reference 52435.

From this point, the river heads to town Catterall, a town, where it meets the River Wyre, a tributary of the River Calder. From the map, it is evident that the two Rivers confluence at approximately 300 meters east of the A6 Catterall playing fields. There are two schematic reservoirs used on the River Calder – Grizedale Lea Reservoir and the Barnacre Reservoir. They are both located at about grid-reference 5448.

We have visited and investigated five different locations along the river’s course, and these are:

Location #1– approximately 4km from source. Grid reference 548 487.

Location #2- approximately 5.2km from source. On Grid reference 539 482.

Location #3 – On Calder Vale: approximately 8.3km from source. Grid Reference 533 482.

Location #4 – Sandholme Mill: approximately 11.4km from source, grid reference 517 434.

Location #5- Catterall playing fields: approximately 14.3km form source, grid reference 494 433.

The information collected at these locations will then be used to see if they meet our original enquiry; whether they do or do not fit the Bradshaw Model.

These are the following factors that that the Bradshaw Model demonstrates, and I will investigate:

Channel Width
Channel Depth
Water velocity
Discharge
Gradient
Average bed-load size
Bed load roundness.

These are the changes that will occur in the factors as they go downstream, according to the Bradshaw model. Thus these will be my hypotheses for investigation:

Channel Width- Increase moving down-stream;
Depth- Increase moving down-stream;
Water velocity- Increasing down-stream slowly;
Discharge- Increases heavily down-stream
Gradient- Slightly decreases down-stream;
Average bed load size- bed load decreases moving down-stream

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These are the following factors that that the Bradshaw Model demonstrates, and I will investigate:

Channel Width
Channel Depth
Water velocity
Discharge
Gradient
Average bed-load size
Bed load roundness.

These are the changes that will occur in the factors as they go downstream, according to the Bradshaw model. Thus these will be my hypotheses for investigation:

Channel Width- Increase moving down-stream;
Depth- Increase moving down-stream;
Water velocity- Increasing down-stream slowly;
Discharge- Increases heavily down-stream
Gradient- Slightly decreases down-stream;
Average bed load size- bed load decreases moving down-stream

A specific analysis of each factor is listed in the ‘theory’ section, which is next.

Theory

1 - Channel Width

The Channel width is expected to increase moving downstream. This increase is due to water being constantly added by the river’s tributary, the River Wyre, along the course of the river. This additional water creates more volume and thus leads to great discharge (5), making the channel width increase. Therefore we expect the river to be wider at site 5 than at site 1. This is shown on the graph in the Data Presentation part of the coursework file along with the area of the river bed (Channel Depth).

As more of this water is added by tributaries, the river’s velocity (3) increases. Velocity is the speed of the river’s flow. The increase in velocity results in a faster erosion rate by ‘Hydraulic action’. Hydraulic action erodes the channel effectively due to the vast amount of water and force the river is provided with by the tributaries’ additional water resulting in an increased velocity rate.

Another method the river erodes is by abrasion, the scraping of a rock surface by friction. The more the channel’s width decreases the great the amount of rocks there will be subsiding on the river’s bed. These rocks exist due to the initial erosion by hydraulic action.

All of the above factors explain why the Channel Width is expected to increase.

2 - Channel Depth

We are expecting the channel depth to increase moving downstream from the source. Therefore we expect site 5, 14.3km away from the source, to be, on average, wider than site 1. This is shown on the graph in the Data Presentation part of the coursework file.

Again, like the Channel Width, the channel depth increases via similar erosion processes which are listed above (1).

3 - Water Velocity

According to the Bradshaw Model, the velocity of the water is expected to increase moving downstream. Therefore we expect site 5 to have a higher velocity than site one. However this is not demonstrated in the Data Presentation part of the Coursework. Reasons as to why this might have occurred will be explained in greater detail in the Data Interpretation.

The upper course is a narrow, large angular channel bed-load. Initially, anyone would have thought that the velocity of the water would be expected to decrease going downstream as the river bed becomes wider. This is not the case, even though the gradient is at its steepest in the upper course, the water, going down, is faced by a ridged wetted perimeter, which acts as an obstacle – making the water’s movement slower. The only exception where the speed of the upper course’s water movement is faster than the lower course’s is when a large storm happens; this is because of the hefty of gush of water. Hence, this hefty gush of water will lead to a higher velocities and the steepness of the gradient (4), will lead to a greater influence of gravity. With this, Hydraulic action will occur, easily surpassing obstacles which it meets. A river cannot normally do this because its speed slows down as it meets the ridged wetted perimeter.

The lower course, on the other hand, has a higher velocity because the river’s bed is smooth, thus there is little to no friction as opposed to the extreme friction created by the wetted perimeter in the upper course. The minimised friction allows the water to flow faster, and this is why the water is expected to increase moving downstream.

4 - Gradient

According to the Bradshaw model the river’s gradient is expected to slightly decrease going downstream. The gradient is the slope of the river bed. The gradient, because of its steepness, is useful for transporting angular loads in the upper course after a heavy storm. During their transportation, they undergo the same erosion processes as the Channel Width (1) and Channel Depth (2). Therefore we expect the slope at site 5 to be smaller than the slope at site 1. This was clearly the case and is demonstrated in the Data Presentation part of the coursework folder.

The gradient decreases going down to the lower course because it is reaching flat, smooth laminar sea surface; it is a flat, smooth laminar surface because there are no boulders, the rocks are well rounded (7) and the bed-load size (6) has declined. The river at the lower course is much deeper in comparison to the upper course, meaning there is a loss of steepness, hence a decrease in the gradient. This is because of erosion processes which make the channel width wider from the upper to lower course.

5 - Discharge

According to the Bradshaw Model, the Discharge will increase heavily going downstream. Therefore we expect site 5 to have a much higher discharge than site 1. However, as with the velocity, this was not the case. This is because the velocity is in the discharge formula and thus a lower velocity will lead to a lower overall discharge.

Discharge is the amount of water passing through a particular point per unit of time. This is the equation I will be using to work out the Discharge:

Discharge (m3/sec) = Cross sectional arena (m2) * Velocity (m/sec)

The river’s cross-sectional area can be worked out by using the Channel Width, which is also expected to increase. This means that more water is likely to pass downstream per unit of time and this is evident by the increased velocity, as mentioned earlier, and the increased Channel Depth, which means an increased supply of water because the downstream is going deeper into the sea towards the shore.

6 - Bed-load size

According to the Bradshaw Model, the Bed-load size is expected to decrease going downstream. Therefore we expect a smaller load at site 5 than at site 1. This was clearly demonstrated as the bed-load size chronologically declined as we went further from the river’s source.

The River Calder, in the upper-course, starts with large angular boulders which take up a lot of space thus increasing the bed-load size. These lead to a lower velocity rate despite the river’s fast flow in the upper course (5).

The great amount of discharge going downstream means that the velocity and surface-area will increase. This means that rocks are likely to be eroded by Hydraulic action especially after a large storm. Some of the larger boulders will fall, because of the steeper gradient and during their rapid transportation; they are likely to collide and rub material off each other, which is called attrition which results, as they are down at the lower course, in smaller rocks.

These smaller rock versions of the large boulder will then sink to the surface in the lower course where they, because of the extreme transportation, are likely to abrade slowly and eventually wear out.

Bed-load roundness

According to the Bradshaw Model, the bed load roundness is expected to increase going downstream. Therefore we expect site 1 to have a higher percentage of angular rocks as opposed to site 5 which will in contrast have a higher percentage of rounded rocks. This is clearly the case in our results, and is demonstrated in a graph which can be found in the Data Presentation part of the coursework folder.

At the upper course, we expect to see rocks which are angular because those rocks are new, large, ridged boulders which did not undergo any erosion processes which did not come in contact with the river’s bed surface in the lower course.

These rocks become more rounded as they are transported from the upper course to the lower course. This happens by the force of water that is summoned during the storm resulting in Hydraulic action; which breaks parts of the boulders into rocks. These rocks, as they are transported, undergo erosion, mainly abrasion, where they rub their materials on the river’s bed, making them smoother as they simultaneously transport to the lower course. From the Middle to the Lower course, rocks tend to move by Saltation. Saltation is the movement of middle-sized particles. These particles tend to move by rolling along the river bed; making them more rounded and smooth.