Get That Grade

GET THAT GRADE!
Unit 04

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Test 3 Feedback

Rivers

Here is the feedback and answers to the Test in Unit 03.

1	(a)	You should have labelled the storm hydrograph as shown here.
	(b)	(i)	25 mm
		(ii)	68 mm
	(c)	(i)	More likely	The water runs down the steep sides more quickly. There is less time for water to infiltrate into the soil.
		(ii)	Less likely	Permeable rock will allow water to penetrate, so there is less water to run off over the surface.
		(iii)	More likely	The trees cannot intercept and slow down rainfall. Roots do not take up water leading to evapotranspiration. There are no root spaces to help water penetrate into the soil. In the longer run there are no roots to bind the soil together, so soil erosion takes place, which may block river channels.
		(iv)	More likely	The rain would have saturated the soil, so there are no pore spaces and water runs off more quickly.
		(v)	Less likely	Drains were put in place to get water off the fields quickly and into the rivers. If they are not working, the water lies on the surface for longer and does not flood into the river.

2	(a)	Hydraulic action	The force of the water breaks the rock, often by forcing its way into cracks and pore spaces and compressing trapped air.
		Abrasion	The stream uses particles that it has picked up to wear away at the banks and bed.
		Attrition	Particles that are being carried by the stream knock together and get worn down.
		Solution	Rock is dissolved by the chemical action of the water.
	(b)	They erode downwards faster than they erode sideways. This is because they tend to run straight with few meanders, and turbulence and causes particles to be swirled round and erode the bed.
	(c)	Your labelled diagram should look something like this.

(a)

Whichever feature you choose you should make the description as precise and thorough as possible. You have to give at least three points to gain full marks. But note that you only have to describe here. You do not need to explain how the feature was formed because that comes in the next part of the question.

For example:

I have chosen a meander. In a meander the water goes round a bend. On the outside of the bend the river is deeper, and it often has a river cliff where the bank is undermined. On the inside of the bend there is a gently sloping slip off slope made of silt.

(b)

If the question says 'you may use diagrams' you should always try to use at least one. The examiner is reminding you for your own good. You should be able to get full marks without a diagram, but it is easier to get marks if you do use one.

For instance:

Oxbow lakes are formed when meanders are eroded. The current is concentrated on the outside of a bend, and erodes it (Diagram 1). Gradually the 'neck' of the meander gets narrower (Diagram 2). Eventually, in a flood, the river cuts right through the neck, leaving the oxbow. Silt is deposited and cuts it off from the main river (Diagram 3).

You could use the River Derwent as an example:

The River Derwent flooded in 1999 and many houses in Malton had to be evacuated. To try and stop this happening again the Environment Agency have started to dredge silt that has been deposited in the river below Malton. They have also cut down trees and bushes and reeds that were growing on the banks and bed of the river. This means that the water drains away from Malton more quickly. It is hoped that this will prevent the river from flooding in future.

People further downstream in Stamford Bridge complain that speeding up the water flowing away from Malton just gets it to their houses more quickly and makes their floods worse. They are also annoyed because clearing the vegetation is destroying habitats that were popular with birds such as Kingfishers. If the habitat is destroyed, the birds will disappear.