River study - Burbage Brook,

Middle Course of Burbage Brook

The middle course of Burbage Brook is a 'V within a V' shape. The valley is slightly wider here than the upper course of Burbage Brook also the valley sides are much gentler. It also meanders side to side caused by interlocking spurs (look at the diagram below about a meander).

The valley sides widen due to lateral erosion. Lateral erosion takes place here because the velocity of the river is much slower than what it is at the upper course of Burbage Brook (refer to the middle course bar chart of Burbage Bridge to find out the velocity). Also gradient is not as steep, which causes the river to slow down and start to form a meander (side to side). All this causes the valley to widen out and erode the interlocking spurs.

If you look at the cross-section of the middle course of Burbage Brook that I have produced you will see that the river is now wider and deeper here, another reason for the river to become deeper is due to tributaries leading into the brook.

Another cause to the 'V within a V' shape is due to the changes in rock type (look at the diagram below to show how the changes in rock type work). The rock changes from Millstone Grit to Shale. Millstone Grit is very resistant to weathering because it is a very hard rock but because of the joints and planes it tends to get a lot of freeze-thaw weathering occurring. Because this rock is very hard it is resistant to river action so it takes years for it to erode. Shale is a very soft rock formed from deposits of mud and silt compressed to form a rock. This rock is easily broke apart, wetting and drying causes the rock to expand and contract repeatedly and then eventually causes the rock to disintegrate. Also this rock is not very resistant to river action as it gets eroded (under-cut) very easily, which may often cause a landslide (look at the photo below of evidence of a landslide).

Lower Burbage Brook

The lower course of the valley is a lot wider compared to the upper course; the sides are now a lot gentler. A floodplain has now formed and the valley meanders.

Due to the gradient being gentler in this area it makes the velocity of the river even slower (see bar chart on lower Burbage bridge for information on the velocity). Because the velocity of the river has decreased dramatically it widens the rivers banks also caused by lateral erosion (erosion/breaking down of rocks, sediment river banks etc. from the sides), making the current of the river so slow it deposits a load called alluvium. The alluvium deposit gradually causes the river to form a floodplain. The river here is now a lot wider and deeper (see cross section for information on what the river is like in this particular area)

This photograph shows how the lower course of Burbage valley has changed compared to the upper and middle courses. For example it is a lot wider as you can tell and also you can see the floodplain which has formed, also you can see the alluvium which has been left due to the slow velocity.

Other Things

Due to a lot of people using the valley for personal uses, for example walks, rock climbing etc, there has been some human activity taking place like footpath erosion. This is caused by a lot of people using the area and caused that particular area to erode.

Some past conditions like greater freeze-thaw

weathering caused in the 'ice age' when temperatures

where below freezing for a long period of time causing

a lot of freeze-thaw weathering to occur. This is

where water gets into the cracks in the rock, expands

(freezes) which then puts pressure on the rock

eventually causing chunks of the rock to break off

leading to a form of mass movement (Rock Creep).

Burbage Valley Task C Keira McAleese