Abhainn Srath na Sealga: a river study

This piece of work is aimed at 14-18 year old pupils or those interested in developing a knowledge and understanding of the physical geography of rivers.This study is best followed after an introduction to the subject. Access to Ordnance Survey Landranger series sheet 19 would be helpful to further this study and is needed for some of the tasks. Tasks are set at two levels with those in B being more demanding.

Photograph 1 (092730, south)

This view was taken from next to the ruins named 'Feinasheen' on the map. There is little sign of running water in this scene of heather covered peat and rushes. The watershed between east and west flowing rivers is unclear in this deep U-shaped valley.

Task A

1.1 What is the name for where a river starts?

1.2 What is a watershed?

1.3 What evidence is there from the photograph that this landscape has been glaciated? There is a clue in the text .

Task B

1.4 This photograph was taken near to its source. Describe three types of source that a river could have.

1.5 How could a watershed be easily demonstrated?

Photograph 2 (085730, southwest)

This photograph, looking up Bealach na Croise, was taken less than a kilometre from the previous one but shows clear signs of running water. It could easily be argued that the principal source of the river lies in Bealach na Croise.

Task A

2.1 Name any river features can be seen in this photograph?

2.2 What evidence is there of erosion?

2.3 What evidence is there of deposition?

Task B

2.4 By what means has the flow of the river become greater between the source and here?

2.5 Use map evidence to support the statement in the last sentence in the text.

Photograph 3 (081734, north)

The valley and loch in the photograph lie along the line of a major fault. The glacier which moved down this valley would have found this line of weakness easier to erode than the surrounding undisturbed rock.

Task A

3.1 What is the loch an example of (albeit an short one)?

3.2 Using the map to help, what term could be used to describe the feature crossing the view in the foreground.

3.3 Is there any evidence on the photograph that the there has been a change to the foreground since the map was drawn? (look at the left foreground)

Photograph 4 (087775, southwest)

Task A

4.1 Describe in detail what this photograph shows.

Photograph 5 (090794, south)

This view looks up the river towards Loch an Nid, seen in photograph three. The river here has changed its course; the short stretch of water in the centre of the photograph shows where the river used to flow. The river here is beginning to show signs of a river in its middle course.

Task A

5.1 What is the term for the feature in the centre of the photograph left when the river changed its course?

5.2 Under the headings of gradient (slope), width, depth, valley floor,describe the difference between a river in its upper and middle courses.

Task B

5.3 Using the map for extra information, label a sketch of the photograph to show river features, names given on the map and any other geographical features.

Photograph 6 (089791, southwest)

This close-up of the feature shown in the previous photograph shows it is some time since the river flowed along this course. It is slowly filling and becoming a part of the river's floodplain.

Task B

6.1 Describe the process of infilling that is taking place.

Photograph 7 (075790, northeast)

The river here is meandering on a broad floodplain. In middle right can be seen the semi-derelict house of Achneigie.

Photograph 8 (073805, southeast)

This general view of Eilean a' Chip is included to show the process of change that took place between 1994 and 1998. The river in 1994 was taking the course shown on the map but was in the process of cutting through the meander along the straight line. By the time this photograph was taken, in 1997, the change was almost complete. It would seem that this change in the river's course has been a regular occurrence.

Photograph 9 (077801, south)

This view, taken in 1995, shows the pool which was overflowing across the river's floodplain. This pool had probably formed after the main channel became blocked when the river was in spate. The stones on the far side of the pool are those which were deposited at that time.

Photograph 10 (077801, southwest)

This photograph was taken looking to the right of the previous one. In the background will be seen the main channel while in the foreground is the floodplain over which water was flowing. It is clear that at times of high rainfall, large volume of water flowed over this area as can be seen by the tree stumps. On the far right, just visible, is one of the low waterfalls where the river was cutting back to form a new channel.

Photograph 11 (077801, southeast)

The waterfalls referred to in the previous photograph can be seen in this view looking upstream. While erosion was rapid compared to waterfalls on solid rock, the grass was helping to bind the sand and gravel slowing the river's erosion.

Photograph 12 (077801, southeast)

By 1997, the river had cut back to about seven metres of the pool. The grass where the water had been flowing had died by this time and the flow of the water was more easily seen.

Photograph 13 (077801, northwest)

The new channel created by the upstream movement of the waterfall is shown in this view.

Photograph 14 (077801, southwest)

This photograph taken in 1998 shows the river having completed the change in its course. The view should be compared with photograph which was taken from a similar location.

Task A

14.1 Refer to the O.S. map and use the information from photographs 8 to 14 to draw a labelled sketch-map of the changes in the river's course.

Task B

14.2 Write a detailed and illustrated account of the changes in the river's course.

Photograph 15

(073805, southwest)

There is further evidence of the change in the course of the river in this photograph.

Task A

15.1 How is the semi-circular feature in the photograph indicated on the map?

15.2 What evidence of erosion is shown on this photograph and why is it happening where it is?

Photograph 16 (070808, west)

The river broadens in its final kilometre before reaching the ribbon loch shown here. It is joined by another river from the south. The river is still some way from the sea but this is a natural break at which to leave it.

Task A

16.1 Name a. the loch; b. the mountain on the left; c. the mountain beyond the one on the left; d. the river joining from the south.

16.2 What is the term for where a river joins another?

16.3 What term is used for the smaller river joining the main one?

Task B

16.4 On a piece of tracing paper, plot the river being studied and its watershed from its source to where it is met by the river referred to above.

16.5 Calculate the river's catchment area.

Summary

Using map, photographs and text, draw a map to show all the main features of this river. This could be added to the tracing if task 16.4 was completed.